--- type: Whitepaper title: "The Power to Never Be Wrong: Evasions and Anachronistic Attacks Against Web Archives" description: Studies eight web archives using instrumented pages and crawler metadata. It shows how CSP or script stripping and server-side cloaking distort captured content, while future archive references and live-web escapes let publishers alter old snapshots. All eight services exhibit an evasion weakness, and seven permit anachronistic manipulation under the tested conditions. resource: "https://www.securitee.org/files/kirchner_power_ccs2025.pdf" tags: [whitepaper, webseclist-reference, acm-ccs, csp, same-origin-policy, xss, dom, tls, measurement-study, abuse-of-functionality, owasp-a01-2021, owasp-a02-2021, owasp-a03-2021, owasp-a04-2021, owasp-a05-2021] generated: by: webseclist-refs/1 at: "2026-09-10T14:51:13+00:00" status: stable stale_after: 2027-09-10 sources: - id: original resource: "https://www.securitee.org/files/kirchner_power_ccs2025.pdf" title: "The Power to Never Be Wrong: Evasions and Anachronistic Attacks Against Web Archives" author: Robin Kirchner, Chris Tsoukaladelis, Martin Johns, Nick Nikiforakis also_at: [] authors: - Robin Kirchner - Chris Tsoukaladelis - Martin Johns - Nick Nikiforakis canonical_url: "" cited_by: - "2025.md:107" commit: "" content_sha256: d2f1de1b47c011fcb99097830e95970588df43e50081bc5f2840c797e0017058 depth: full depth_reason: default kind: whitepaper language: "" licence: unknown original_url: "https://www.securitee.org/files/kirchner_power_ccs2025.pdf" published: "" publisher: ACM CCS publisher_english: "" raw_sha256: dd5225847780802780b962828d80a7708b02843aeca4d443e43f39ea2a16698c retrieved_from: "https://www.securitee.org/files/kirchner_power_ccs2025.pdf" retrieved_kind: manual-import retrieved_utc: "2026-09-10T14:51:13+00:00" slug: power-never-be-wrong-evasions-anachronistic-attacks-against-web-archives snapshot: "" title_english: "" translation_file: "" translation_of: "" --- # The Power to Never Be Wrong: Evasions and Anachronistic Attacks Against Web Archives **The Power to Never Be Wrong: Evasions and Anachronistic Attacks Against Web Archives** - Robin Kirchner, Chris Tsoukaladelis, Martin Johns, Nick Nikiforakis, ACM CCS. - Published: date not stated - Original: - Preserved from: https://www.securitee.org/files/kirchner_power_ccs2025.pdf (manual-import) on 2026-09-10 - Licence: unknown Rights remain with the original author and publisher. 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The Power to Never Be Wrong: Evasions and Anachronistic Attacks Against Web Archives Robin Kirchner Chris Tsoukaladelis Technische Universität Braunschweig Stony Brook University Braunschweig, Germany Stony Brook, USA robin.kirchner@tu-braunschweig.de ctsoukaladel@cs.stonybrook.edu Martin Johns Nick Nikiforakis Technische Universität Braunschweig Stony Brook University Braunschweig, Germany Stony Brook, USA m.johns@tu-braunschweig.de nick@cs.stonybrook.edu Abstract 1 Introduction The Web is subject to link rot, where links break as webpages are In the late 90s, while the Web was still relatively young, people updated or deleted. Web archiving services, such as the Wayback identified the problem of link rot. Link rot refers to web links that Machine, have emerged as a key solution to address link rot by break over time and no longer direct users to the content they orig- archiving web content and preserving the look and feel of websites inally pointed to. Whether because a specific webpage was deleted, over time. These services offer critical functionality to users, serv- a website went defunct, or the original content was replaced with ing as a historical baseline for an ever-changing Web. Implicit in unrelated content, link rot affects the usefulness of web links over everyone’s use of these services is that they are capable of providing long periods. For example, as early as 2003, researchers identified an accurate record of the past and can, therefore, provide reliable that almost 5% of links crawled from the general Web were bro- ground truth for comparing the past to the present. ken just two weeks later [12]. Later studies discovered that a large In this paper, we demonstrate that this implicit assumption does percentage of links embedded in academic publications and legal not necessarily hold. To this end, we propose two new threat models documents suffer from link rot [18, 40, 63, 64], even to the point against web archiving services in which attackers can exert con- of affecting documents from the US Supreme Court [37]. More re- trol over how their websites are archived. Evasive adversaries can cently, researchers discovered that almost a quarter of the links to distinguish crawlers operated by web archiving services from regu- COVID-19 dashboards that were released during the COVID-19 lar users, selectively denying or altering the content delivered to pandemic were broken just one or two years later [3]. the former. Anachronistic adversaries can not only identify archive Web archiving services emerged as one of the key solutions to crawlers but also deliver content that enables them to retain control address link rot, among other digital preservation needs. These over archived snapshots. By abusing fundamental access-control services work by visiting links and indexing their contents, making mechanisms of the Web, these attackers can effectively alter the snapshots available to the public as they appeared on the day they past as recorded by web archiving services. We found that all web were archived, even if the original links break or eventually point archives we investigated suffer from one or more of these issues, to different content. As of January 2025, the Internet Archive—the challenging our current reliance on them. world’s most popular web archiving service—preserves a collection of over 900 billion webpages going as far back as 1996, demonstrat- CCS Concepts ing both the scale of digital preservation but also society’s reliance • Security and privacy → Web application security. on such services [23]. Next to individual users manually requesting the archiving of pages, cornerstone web services, such as Wikipedia, Keywords rely on web archiving services to combat link rot [24, 60]. Over time, users discovered more and more use cases for archived Web, Archiving, Attacks, Snapshots web pages. Web security researchers have, for example, relied on ACM Reference Format: web archives to study how third-party JavaScript has evolved over Robin Kirchner, Chris Tsoukaladelis, Martin Johns, and Nick Nikiforakis. time [43], when popular websites first implemented online track- 2025. The Power to Never Be Wrong: Evasions and Anachronistic Attacks ing [36], and how they adopted web-security mechanisms [21, 38, Against Web Archives. In Proceedings of the 2025 ACM SIGSAC Conference on Computer and Communications Security (CCS ’25), October 13–17, 2025, 47]. Outside of computer science, an increasing number of users Taipei, Taiwan. ACM, New York, NY, USA, 15 pages. https://doi.org/10.1145/ rely on archiving services for a multitude of reasons. For instance, 3719027.3765051 patent lawyers use web archiving services to establish the true date that an invention was first described in public [22]. In contrast, some web users identify stealth edits to articles by comparing the This work is licensed under a Creative Commons Attribution 4.0 International License. live versions of those articles against archived ones [19, 28, 41], a CCS ’25, Taipei, Taiwan phenomenon which has been studied in prior work [53]. In addi- © 2025 Copyright held by the owner/author(s). tion, the large-scale removal of web content by governments [50] ACM ISBN 979-8-4007-1525-9/2025/10 https://doi.org/10.1145/3719027.3765051 demonstrates that both commercial organizations like news outlets CCS ’25, October 13–17, 2025, Taipei, Taiwan Robin Kirchner, Chris Tsoukaladelis, Martin Johns, and Nick Nikiforakis as well as public ones like governments exert control over their Table 1: Overview of popular web archiving services, ranked web content in ways that are not always transparent. in descending order of popularity Given society’s increasing reliance on archiving services, it is no surprise that they have recently become targets of attacks. In 2017, Service Name Operating Organization Tranco Lerner et al. [35] demonstrated isolated cases where accidental Ranking remote links and expired domains in archive snapshots could be Wayback Machine[FP] Internet Archive 157 abused to hijack individual snapshots on the Internet Archive. More Archive.Today[CO] Unknown 5535 recently, in October 2024, the Internet Archive was compromised Perma.cc[FP], [$] Harvard Library Innovation Lab 52 432 1 by attackers who exfiltrated a database of 31 million authentication Megalodon[CO] Affility Co. Ltd. 65 845 Ghost Archive[FP] Unknown 128 723 credentials and defaced its landing page [1, 15]. ARQUIVO[FP] Fundação para a Ciência e Tecnologia 249 057 Our work generalizes control over snapshots to all content, FreezePage[FP] USONSE S.R.L. 818 607 across all major archiving services. In this paper, we shed light Conifer[FP] Rhizome n/a on the “invisible” part of web archiving services. Specifically, we [$] Paid service, [CO] content-only archive, [FP] functionality-preserving archive study how exactly these services archive content, both in terms of 1 Megalodon allowed more functionality before its patch in January 2025. fetching web pages using their own crawling infrastructure and rewriting the fetched content so that all previously external re- 2 Background sources can now be served by the archiving service. To this end, In this section, we introduce the in-scope web archives, discuss the we design a web archive observatory and automate the process of different attackers’ motivations and capabilities, and provide a brief requesting the archiving of pages under our control by popular in- background on specific client-side security guarantees that are at ternational and regional archives. We show that attackers can exert risk when rehosting websites under one archive domain. ongoing control over their own archived past, long after archival, something that was previously unheard of. 2.1 Web Archives Given the discovered details of how archiving services employ The Internet Archive’s Wayback Machine is just one of many func- crawlers and how they rewrite content prior to archiving, we tional archiving services. Table 1 shows eight services we identified propose two new types of attackers: i) evasive adversaries and ii) by considering related work and search-engine results. We use the anachronistic adversaries. Evasive adversaries aim to differentiate Tranco list1 [34] for ranking websites. These services vary signifi- archive crawlers from regular users so that they can selectively cantly in ranking, with the Wayback Machine being the 157th most serve different content to the former. We demonstrate how attack- popular website on the Internet and FreezePage being ranked in ers can succeed in this goal by utilizing server-side evasions (e.g., the 800 thousands. The Tranco list does not differentiate between identifying crawlers based on their autonomous systems and TLS subdomains, so no Tranco ranking is known for Conifer. How- fingerprints) and client-side evasions (e.g., using JavaScript code ever, Conifer’s parent organization, Rhizome, is ranked at 21 380. that will only execute when an archiving service rehosts websites). Besides services with a global audience, we also observe regional Anachronistic adversaries can conduct significantly more pow- services, such as Megalodon, which is aimed at Japanese users, and erful attacks where not only can they detect the archiving of their ARQUIVO, which is aimed at Portuguese users. Finally, while the own websites, but they can also affect that archiving to the point identities of the operators of many of these services are known, where they can modify content after it was archived. In this way, the organizations behind two services—Archive.Today and Ghost anachronistic attackers essentially control the past (as recorded Archive—are unknown. Notably, Archive.Today is served under by independent archiving services) and have the ability to “unsay” multiple top-level domains, including .today, .ph, .vn, and .is, of things they said that ended up being wrong, harmful, or unpopular. which archive.is the most popular URL with a Tranco ranking of In summary, we make the following contributions: 5535 and the lowest archive.vn ranked at 40 503. Preliminary tests ● We map the server-side infrastructure of eight web archiving revealed no differences in the behavior and infrastructure of these services, including their crawlers’ IP addresses, ASN, and services. Thus, we decided to limit our testing to Archive.Today, TLS fingerprints. which is the title name given on all alternative URLs of the service. ● We showcase how an evasive publisher can use this infor- Most services are free, donation-based, or offer optional premium mation to conduct targeted server-side cloaking. features. Conifer, FreezePage, and Perma.cc require an account, ● We survey the web archives’ security measures and show while additional URLs have to be bought for Perma.cc after an how attackers can bypass these defenses to carry out evasive initial set of 10 free archived pages. and anachronistic attacks. There is an implicit user expectation that web archives pro- vide unchangeable, truthful records of websites. The archives rein- In addition, we propose two novel classes of evasions against force this expectation through statements such as: “Websites change. web archives: CSP Stripping and Script Stripping. We show that Perma links don’t.”— Perma.cc [45], “Prove exactly what was at a web CSP Stripping is particularly effective and broadly applicable, as address at a specific date and time.”— FreezePage [16], “Capture a demonstrated across all web archiving services (ref. §5.3.2). web page as it appears now for use as a trusted citation in the future.”— Internet Archive [25], “Ghostarchive will store a snapshot of the web- Given the highly visual nature of our proposed attacks, we have site as it appeared at the time of archival.”— GhostArchive [17]. recorded extensive demos for all presented attacks against all ser- 1 vices and made them available in Section 5.1. Generated on 22 January 2025 and available at https://tranco-list.eu/list/4QJ3X. The Power to Never Be Wrong CCS ’25, October 13–17, 2025, Taipei, Taiwan However, our analysis reveals that most defenses are insufficient changes. Likewise, governments may oppose archiving when it to prevent post-archival modifications to snapshots (ref. §5.3). exposes inconsistencies or documents that were later removed. Functionality-preserving web archiving. Functionality-preserving Malicious websites. There can be multiple reasons that malicious archives like the Wayback Machine rehost a page with all its subre- websites want to detect visits from web archiving services. Mali- sources. This is invaluable for creating a memory of the Web as it cious sites have long engaged in cloaking [26, 55, 62] to differentiate was in the past, including all of its technologies and vulnerabilities. between visits from security crawlers and those from prospective These archives singlehandedly enabled web research over the years, victims. When a malicious website detects a visit by a security such as the study of historic security vulnerabilities [e.g., 43, 52]. As crawler, it may hide its real malicious content by, for example, redi- an example, snapshots of OpenStreetMap in the Internet Archive recting users to benign websites. Similarly, malicious sites that still allow scrolling and moving on the map2 . attempt to rank highly on search results can show different content to search engine crawlers than to result-clicking users. We antici- Content-only web archiving. Even though the majority of web pate malicious sites may want to evade web archiving services to archives try to preserve a website’s core functionality, alternative increase the longevity of their attacks and have later deniability as approaches exist. Archive.Today, as a prominent example, removes to what exactly was served by that website. all interactive functionality of the page it captures, primarily aim- ing to retain a website’s final rendered appearance. In contrast 2.3 Attacker Model to the Wayback Machine’s snapshot, Archive.Today’s snapshot of We present two primary adversaries: the evasive adversary, and the OpenStreetMap is non-interactive3 . anachronistic adversary. Both attackers (ab)use characteristics of the archiving services to exert control over the creation of snapshots of 2.2 Reasons for Evading Web Archives the adversary’s website. Thus, they break the assumption that all We argue that the threat model of websites altering their own content shown in a snapshot existed like this at the time of archival. archived past is not only realistic but increasingly relevant. Prior We acknowledge that not all content creators want their pages to studies have revealed that news websites engage in stealth edits [53], be archived, which we believe is a legitimate viewpoint. Malicious silently altering content after publication. Moreover, governments evasions, escapes, and anachronistic manipulations, however, go have been shown to actively remove web content at scale [50]. beyond personal preference and subvert the integrity of archives. Despite the trust in archival permanence by legal, journalistic, and scientific communities, recent findings challenge that trust [35]. 2.3.1 Evasive Adversary. The evasive attacker aims to prevent their Undermining that assumption of permanence, especially after the web content from being properly archived by: initial archival, has radical and cascading implications. ● Detecting and blocking archive service crawlers, We differentiate between benign and traditionally malicious ● Serving different content to archiving service crawlers, or websites when systematizing why website operators may have an ● Exploiting technical characteristics and limitations of archiving interest in avoiding their websites being archived or in controlling services to prevent complete content capture. what content gets archived. An evasive adversary can target either all web archives or spe- cific ones. Making snapshots of the adversary website unusable in Benign websites. Prior research has shown that some users utilize specific archives can entice web archive visitors to resort to alterna- web archiving services in ways that may financially hurt the web- tive archiving services, which the adversary potentially has more sites being archived. For example, Zannettou et al. established that control over. some users resort to archiving services to deny ad revenue from 2.3.2 Anachronistic Adversary. The anachronistic attacker attempts websites that they consider objectionable, e.g., due to disagreements to modify archived content after it has been captured by: between the perceived political leaning of a website vs. the one of ● Exploiting URL-rewriting mechanisms to inject future references these users [61]. By sharing archived links (instead of live links) on to other archived resources, social media, news sites would lose page visits and the associated ● Injecting references to external resources that “escape” the archive, ad revenue from these impressions. Tsoukaladelis et al. discovered ● Taking advantage of JavaScript execution in archived pages. that news sites often change their articles post-publication in a way that frequently exceeds the mere fixing of typos and benign 2.4 Web Security Policies rephrasing [53]. These often-silent post-publication changes are an unwanted side effect of online news, prompting users to increas- The Same-Origin Policy [8] (SOP) and the Content Security Pol- ingly rely on web archives as their source of ground truth—that is, icy [59] (CSP) are the Web’s most important client-side security to verify what an article stated at the time it was archived. There are policies for our work. multiple reasons why even reputable websites might wish to “unsay” The SOP is a fundamental access control policy of browsers that something they previously published by controlling or restraining restricts how web documents and resources from different origins web archiving. For example, organizations engaging in stealth edits can interact. In the context of web archiving, third-party websites may wish to avoid leaving publicly verifiable evidence of these are often rehosted under the archive’s own domain. This would break its functionality without adjustments to the pages, as the 2 browser would block all third-party resources when the page is Snapshot of OpenStreetMap in Wayback Machine https://web.archive.org/web/ 20250211015148/https://www.openstreetmap.org/ (2025-02-11). hosted under the new domain. For this reason, web archives often 3 Snapshot of OpenStreetMap in Archive.Today https://archive.ph/7oVH3 (2025-02-23). capture subresources, like images, scripts, and documents, and then CCS ’25, October 13–17, 2025, Taipei, Taiwan Robin Kirchner, Chris Tsoukaladelis, Martin Johns, and Nick Nikiforakis Page and URL Automated Service Filtering and Data Generation Interactions Analysis Figure 1: Overview of our archive observatory, which includes instrumented websites on multiple domains, automated archive interaction, and data analysis. rewrite references to these resources on their copies of the captured fingerprints. The information recorded by our platform can later be websites. Oftentimes, scripts have to be rewritten as JavaScript APIs used to recognize archiving service crawlers and study the services’ like document.domain or window.location would return unexpected vulnerability to evasion and anachronistic attacks. values under the new domain. The CSP is a directive-based security policy that controls which 3.1 Website and URL Generation resources a page can load. Its purpose is to mitigate security risks The passive part of our observatory involves serving an extensive like cross-site scripting (XSS) by defining the origins from which number of instrumented websites. To allow us to attribute crawler scripts are allowed to run. When a web archive service rehosts behavior and isolate its characteristics confidently, we distribute our a website, it is challenging to rewrite that website’s original CSP architecture over ten instances, each carrying a separate domain. to ensure that the rewritten resources are not blocked. Therefore, Each observatory instance acts as a honeypot, serving arbitrary one of the discoveries of this paper (Section 4.1.1) is that archives subdomains and URLs of the respective domain while collecting typically strip a website of its CSP when rehosting it, potentially metadata about its visitors. replacing it with the archive’s own CSP if it has one. 3.1.1 Crawler Client Fingerprinting. The generated observatory web pages include state-of-the-art TLS client fingerprinting tech- 3 Web Archive Observatory niques to understand and map the capabilities of different web To achieve our goal of mapping and quantifying existing archiving archiving service crawlers. services, we must examine what happens with websites when web TLS Fingerprinting. We adopt the JA3 [48] and JA4 [14] TLS fin- archiving services create snapshots. Web archives use crawlers gerprints (initially intended for threat detection) to differentiate to visit pages they want to create a snapshot of. Studying these between archive crawlers based on their TLS stacks. TLS finger- crawlers in the wild is best done by triggering archiving requests printing operates on the Client Hello packet that is transferred for controlled websites. during the initial TLS handshake to establish an encrypted connec- Our web archive observatory platform automates the process of tion between the client and the server. Salesforce’s JA3 [6] method archiving instrumented web pages via different archiving services uses information from the Client Hello, including the TLS version, and helps evaluate collected metadata like network information TLS extension lengths, and cipher suites, to create a TLS fingerprint and client fingerprints. Figure 1 illustrates this platform, which of the TLS client’s configuration. The more recent JA4 method combines both active and passive components and operates as a reduces the number of fingerprints for modern browsers by ac- honeypot accessible under a specific domain. Each deployment of counting for the randomization used by these browsers during the our platform constitutes a separate observatory instance with its TLS handshake [10]. For a later comparison of archive crawlers own domain. The active part of our platform attracts visits from with the fingerprints of current browsers, we collected the TLS fin- web archive crawlers by semi-automatically requesting the archiv- gerprints of the Top 20 desktop browser versions by market share ing of generated, unique links with non-predictable subdomains. from 02/2024 to 02/2025 [51]. The passive part of the observatory serves instrumented webpages for the links generated by the active part, similar to a honeypot. Client-side Browser Fingerprinting. Browser fingerprinting is a When the archiving services’ crawlers visit our unique links after common technique in online tracking that identifies unique devices we requested their archival, our observatory platform records sev- by leveraging JavaScript APIs exposed by the browser [e.g., 13]. Al- eral pieces of information, such as network information and client though we initially considered including browser fingerprinting in The Power to Never Be Wrong CCS ’25, October 13–17, 2025, Taipei, Taiwan Table 2: Unique archiving service crawler endpoints and number of requests to our observatory. Geolocation Meta Information Number of Requests Portugal Canada Russia #VPN IPs Japan Distinct US Other #UAs #JA3 #JA4 Archive Archive Others after IPs / ASNs Crawler(s) 1h 1 day 7 days Wayback 19 - - - - - 19 / 1 0 2 1061 2 1894 +2 10 95 Archive.Today 8 1 - 3 10 25 47 / 27 15 196 3 3 1752 +50 231 262 Perma.cc 4 - - - - - 4/1 4 42 4 4 2321 +60 551 2759 Megalodon - - - 3 - - 3/1 3 2 1 1 1950 - 197 246 Ghost Archive 1 - - - - - 1/1 1 1 2 2 1100 - - - ARQUIVO - - 2 - - - 2/1 0 4 2 2 1552 - - - FreezePage 1 - - - - - 1/1 1 3 1 1 978 - - - Conifer 1 - - - - - 1/1 1 2 2 2 1365 - - - our observatory study, we ultimately chose not to do so for multiple anti-bot measures via Cloudflare. Hence, we manually conducted reasons. A primary goal of the observatory is to support server- our archiving requests for that service. side detection of archive crawlers. This requires that distinguishing A save-page experiment for any of the ten observatories entails information is available in time for the server to tailor its response assigning a random unguessable alphanumeric subdomain for the to a request. However, browser fingerprinting does not meet this experiment. The observatory creates a record for that archiving criterion, as the relevant results become available only after the request in its database, associating the newly generated URL with client executes JavaScript included in the server’s response. By that the archiving service. The archival timestamp is stored after the point, the website’s content has already been delivered to the client. page is saved using the respective web module for the archiving The browser fingerprint could still be used in the client-side service’s save-page process. This data can later be used to associate code to detect archive crawlers by comparing their fingerprint visits to our observatory addresses and the entailing characteristics, against a list of known crawler fingerprints and altering the website e.g., HTTP headers, TLS fingerprints, with the archiving service accordingly when viewed by an archive crawler. However, the crawlers. archive crawler acts as a client only during the capture. After the archival process, archive visitors are the clients, which can lead to 3.3 Filtering and Data Analysis unintended side effects. In the last part of the observatory , we analyze the collected data Moreover, Gómez-Boix et al. [20] observed a declining number regarding each archive’s crawlers. In the presence of unrelated web of unique browser fingerprints and found that non-unique finger- scrapers and scanners, we must ensure that the visitor data we use prints are brittle. According to their findings, the trend of modern belongs to the crawlers of the archiving services. Our primary filter- browsers to reduce plugin support substantially lowers fingerprint ing mechanism involves generating observatory pages with unique uniqueness, and even small changes to a single feature can signifi- alphanumeric subdomains to differentiate between archive crawlers cantly affect the overall fingerprint. For these reasons, we ultimately and unrelated visitors. For instance, visits to https://observatory.test decided against using browser fingerprinting in our study. may come from a wide range of scanning bots, but a visit to a URL like https://2a94b7-97d92f.observatory.test/ that was only revealed to the Wayback Machine at a known time is highly likely, if not 3.2 Automated Service Interactions guaranteed, to be originating from the archive’s crawlers. The active part of our observatory facilitates the archival of Knowing that bots use Certificate Transparency (CT) to identify hundreds of instrumented observatory webpages. All archiving new targets to crawl [29, 46], we rely on wildcard HTTPS cer- services in our study offer a feature that allows users to create tificates to ensure our subdomains are never revealed in CT logs. live website snapshots on demand. The Wayback Machine, for As such, initial visits to a specific subdomain can only originate example, refers to this functionality as “Save Page Now.” Following from the archiving service, and potential third parties later learning this terminology, we refer to such features as save-page features about it through that service’s data. or save-page requests throughout the paper. We have developed Regarding that last point, we observed that some archiving ser- separate web modules for each archiving service, mimicking how vices offer searching capabilities or public API endpoints4 where users of that service navigate the website and submit save-page newly archived pages can be found. We have to expect requests from requests. We automate the archiving process as much as possible to third-party visitors for these specific archive services. We always at- facilitate saving a sufficiently large number of websites, allowing tribute the first request to an observatory URL generated explicitly us to draw conclusions about the operation of each service. We for an archive to belong to one of the archive’s crawlers. Modern automated this process for Wayback Machine, Archive.Today, Ghost pooled server-side infrastructure sometimes loads the resources of Archive, ARQUIVO, FreezePage, Conifer, as well as Perma.cc by navigating to the respective save-page feature using a browser instrumented with Selenium [11] and a Chromedriver with basic 4 Perma.cc has a public API (https://api.perma.cc/v1/public/archives) where newly bot-detection evasion techniques [54]. Megalodon uses extensive archived pages can be polled. CCS ’25, October 13–17, 2025, Taipei, Taiwan Robin Kirchner, Chris Tsoukaladelis, Martin Johns, and Nick Nikiforakis a single website using multiple crawlers situated on different IP ad- pool of crawling hosts. The Wayback Machine—the most popular dresses. Thus, we attribute requests within an empirically-derived archive service on the Web—operated 19 crawler endpoints, which time window of 5 minutes after the initial request or sufficiently were exhausted after the archiving of 21 observatory pages. similar client characteristics (like IP addresses) to the archive’s As anticipated, the regional services ARQUIVO and Megalodon crawlers. We supplement this with additional filters based on the IP send requests from their respective country of origin, while most ranges of large Internet companies, such as Google or ByteDance, other archives operated crawlers from the US. According to OSINT and publicly accessible lists [42] of known web crawlers. data [2], Archive.Today about a third of the archive’s IP addresses After filtering, we have a database containing metadata about belong to known VPNs. The IPs of Perma.cc, Megalodon, Ghost crawlers from different web archives. This data includes all the in- Archive, FreezePage and Conifer are entirely flagged as VPNs. formation our observatory web pages extracted about each archive The right part of Table 2 shows the total number of requests we crawler, i.e., their IP address, declared user agent, and other HTTP received from archive crawlers and other unrelated clients follow- headers, as well as TLS fingerprints. This data is then further aug- ing the archival of our pages on the respective archives. Perma.cc’s mented using open-source intelligence (OSINT) lists [2] to include choice to publish newly archived URLs in a public API (ref. §3.3) a host’s geographical location, its Autonomous System (AS), and if attracts one order of magnitude more unrelated visits to our web it is a VPN server or a host belonging to a cloud provider. pages after one week compared to the other archives. Most of Perma.cc’s third-party requests come from ByteDance’s ByteSpider 3.4 Observatory Study and Majestic’s MJ12bot, who gather training data for LLM train- To map the observable infrastructure of the selected targets, we ing [9] and search engine improvement [39], respectively. Mega- conducted a partially automated study using our ten observatory in- lodon, and Archive.Today attract a similar amount of third-party stances, which perform automated service interactions for archives visitors, followed by the Wayback Machine with less than half that that can be automated. Each experiment is associated with an archiv- amount. Archives without a public search function did not result ing service and receives a newly generated URL for a randomly in visits to the archived websites. chosen domain of one of our observatory domains. Figure 2 visualizes how the Wayback Machine and Archive.Today For our study, each experiment comprises archiving a new URL differ from the other archives for which we observed precisely one using the respective archive’s save-page feature and observing AS with four or fewer unique crawler endpoints. The graph includes subsequent HTTP requests targeting the experiment’s URL. We only Archive.Today’s ASN data, as all others showed just one ASN. limit automated save-page requests to approximately one save per 3.5.2 Fingerprinting Crawlers. ARQUIVO and the Wayback Ma- hour to ensure we are not overloading the web archive services. chine include the respective archive’s name in some User-Agent The automated archiving experiments were conducted over the headers. The remaining user agents are masked as regular browsers. course of 16 days. The manual experiments for Megalodon were Archive.Today displays a noticeably diverse set of user agents, rang- done over a period of 37 days. Perma.cc is the only paid web ing from different desktop browser versions to mobile browsers. archive service. Thus, it functioned as the floor for our study’s With three-year-old Chrome versions, we received the most out- number of archiving experiments per archive. We opted to purchase dated user agent strings from the Wayback Machine (Chrome 89– 200 links, of which five were used during testing. In summary, 115) and Perma.cc (Chrome 90–131), followed by two-year-old for each web archive, we actively requested the archiving (save- browser versions from Archive.Today (Chrome 100–121) and Ghost page request) of at least 195 controlled URLs, distributed across Archive (Chrome 106). The remaining archives used only recent the ten observatory instances. Each controlled URL carries a newly Chrome user agents during our study. generated, random, and unguessable subdomain (see §3.3 for an All services converge to four or fewer JA4 TLS fingerprints, as example). These controlled URLs lead to observatory pages, each displayed in Figure 2’s right graph. However, the Wayback Machine tied to one specific save-page request. These save-page requests stands out. While we only observed 19 IP addresses, their crawling led the archives’ crawlers to request and create a snapshot of our infrastructure shows a surprisingly large variety in TLS client con- observatory websites. Their visits give us information about the figurations, leading to 1061 JA3 fingerprints after 195 saved pages infrastructure of each archiving service, as described next. over ten days. Diving deeper into the Wayback Machine’s Client Hello parameters reveals that the TLS client offers three typical 3.5 Archive Crawler Infrastructure cipher suites, followed by a selection of other cipher suites, which This section presents the dataset resulting from our observatory explains the various JA3 fingerprints. However, all TLS client config- study with respect to our first research goal of mapping the services’ urations negotiated identical final connection parameters, resulting infrastructure. Table 2 (left) displays the number of unique archive in just one JA4 fingerprint for the Wayback Machine crawler. crawler endpoints we discovered after 195 saved pages. The ever-increasing number of crawler endpoints we uncovered for Archive.Today makes network-based detection of the service’s 3.5.1 Crawler Endpoints. Archive.Today was the archive with the crawlers challenging. The limited crawling vantage points of the most distinct crawlers visiting our observatories, operating 47 dis- remaining archives allow attackers to conduct server-side evasion tinct IP addresses from 27 different autonomous systems. With 19 attacks straightforwardly, which we discuss in Section 4.1.3. different geolocations, it is the only archive service that operates hosts in more than one country. By conducting follow-up exper- 3.5.3 Reflecting the Filtering Method. To test our assumption that iments that requested from Archive.Today to archive additional the generated observatory URLs are sufficiently hard to guess, we URLs, we concluded that we were nowhere near exhausting their checked and found no visits to URLs used in experiments before the The Power to Never Be Wrong CCS ’25, October 13–17, 2025, Taipei, Taiwan Archive.Today Wayback Machine Wayback (JA3) Conifer Archive.Today (ASN) Perma.cc Archive.Today Perma.cc ARQUIVO FreezePage, Ghost Archive, ARQUIVO FreezePage, Megalodon, Megalodon Conifer Ghost Archive, Wayback 50 40 1000 30 #TLS Fingerprints 500 20 #Crawler IPs 10 5 5 0 0 0 50 100 150 200 0 50 100 150 200 Archiving Request Number Archiving Request Number Figure 2: Unique archiving service crawler endpoints contacting our observatory after our archiving requests. experiment started. We conclude that no URL-scraping campaigns Table 3: Formalization of our proposed attacks. were launched against our domains, which would have interfered Adversary Payload Payload Attack Name Scope with our results. ARQUIVO, Ghost Archive, FreezePage, and Conifer Type Source Preparation are our baseline for the filtering. CSP Stripping client n/a before Cross-checking the visitor data from our results database with Script Stripping client n/a before Archive- Server-side OSINT lists revealed a match with the Yandex bot’s user agent, IP Evasion IP-based server n/a before Cloaking Attacks TLS-based server n/a before addresses, and ASN. Namely, Archive.Today occasionally used this crawler immediately after our save-page request. Thus, we conclude UA-based server n/a before this crawler instance is operating directly for Archive.Today. Anachronistic Archive Anachronism client archive anytime Attacks Live-web Escape client live-web anytime False positives in our crawler filtering approach are unlikely due to the short timeframe we allow for crawler visits to occur. Additionally, we observed a wide range of Chrome user agents, with truthful, original appearance, while blue denotes the defaced or the oldest versions being over three years old. Chrome’s automatic manipulated version served by the archive. updating mechanisms make it highly unlikely that human users operate browsers with such outdated user agent strings. 4.1 Archive Evasion Attacks As discussed in Section 2.2, evasive adversaries may want to prevent archives from creating faithful representations of their websites in 4 Attacks against Web Archiving the form of a snapshot. To achieve this goal, they can abuse the characteristics of web archives. First, the evasive adversaries can While web archives effectively combat link rot, i.e., the disappear- incorporate client-side code in their websites that alters a page’s ance of information previously available at a certain Web desti- appearance only when it is hosted in the archive’s context (see §4.1.1 nation, not all website owners share the goal of preservation. For and §4.1.2). Alternatively, these attackers can collect identifying some, especially malicious actors, permanence is a threat rather information about the archive’s crawlers, such as network specifics, than a benefit. Journalists and researchers, for instance, rely on to distinguish between archive visits and regular visits (ref. §4.1.3). web archives to reference past content or study how websites were composed at different points in time [e.g. 21, 36, 38, 43, 47, 52]. In 4.1.1 CSP Stripping. Copying a live website and automatically contrast, malicious actors may seek to evade archival evidence. A placing it in another origin is challenging, as browser security guar- website that temporarily hosts illegal or controversial content may antees are tightly bound to a website’s origin, i.e., its web address benefit from ensuring that no lasting evidence remains in archives. consisting of protocol, domain, and port. One important security Similarly, political entities or publishers may attempt to control mechanism browsers enforce is the Content-Security Policy, which or sanitize the content captured about their web presence. This controls what script resources a page can load. While creating a section proposes five attacks against web archives that aim at one snapshot, keeping the script content of a website is especially dan- or more of these attacker goals. gerous, which is why archives usually have their own defenses or Table 3 summarizes these attacks by their intended effect. CSP policies in place. Thus, archives may opt to ignore the CSP of the Stripping, Script Stripping, and Server-side Cloaking aim to prevent pages they publish as snapshots under their domain. This character- the creation of truthful website snapshots. Archive Anachronisms istic effectively creates archive-only scripts that conveniently only attacks and Live-web Escapes are even more powerful, as they allow trigger when a CSP-stripping archive rehosts the website. Specifi- attackers to influence and control a snapshot’s appearance even cally, an evasive website could define a CSP that disables execution after it has been archived. Figure 3 illustrates a key adversarial goal: of one of its own scripts. When this website is rehosted by a web a website that appears red on the live web but turns blue when archive that strips its CSP, the initially dormant code will be al- rehosted by a web archiving service. Throughout the paper, we use lowed to run. This effectively creates archive-only code which can this color distinction as a running example—red represents the freely alter a snapshot’s appearance on execution. CCS ’25, October 13–17, 2025, Taipei, Taiwan Robin Kirchner, Chris Tsoukaladelis, Martin Johns, and Nick Nikiforakis Our observations from Section 3 indicate that web archive crawlers reveal sufficient metadata about their identity, allowing attackers to perform server-side evasions for most of the studied services. Key Takeaway 1. Archive crawlers can be selectively deceived during snapshot creation. Robots.txt. The robots.txt [30] file can instruct compliant crawlers on which website resources to access, potentially serving as a mech- anism to control what content is visible to different archive user Figure 3: A website’s snapshot appears different ( blue) from agents. However, an ancillary study revealed that the diversity of the live version ( red) due to evasion attacks. user agents is too great, and the in-scope archives either did not request the robots.txt file or disregarded its directives. 1 Content-Security-Policy: script-src-attr 'none'; 4.2 Anachronistic Attacks 2 3
Red Dragons
The term anachronistic attack refers to content that appears out of 4 5 its proper time. Here, an archive (involuntarily) allows snapshots 6 Archive snapshots are typically regarded and advertised as im- mutable representations of a website’s look at the time of archival. In the above example, the evasive website initially displays red However, effective defenses are vital to prevent escapes from the content, illustrated by the HTML div element “team-name” (Line archive’s boundaries, especially with functionality-preserving web 3). The onerror handler (Line 6) is normally blocked by the archiving (ref. §2.1). The anachronistic adversary (ref. §2.3.2) abuses page’s own CSP, which disallows JavaScript inside HTML attributes flaws in these defenses to alter the appearance of snapshots after (Line 1). This block is lifted when the page, excluding its CSP, is re- their creation, allowing adversaries to exert even more control over hosted by a web archive. Therefore, the previously dormant onerror snapshots of their page than with evasive attacks. We distinguish handler runs, modifying the page content that users see ( blue). between archive anachronism and live-web escape. 4.1.2 Script Stripping. Archives that disable script tags facilitate an- 4.2.1 Archive Anachronism. Archive anachronism attacks refer to other attack that relies on the absence of a script. The attack works attacks where the resources later used to alter a snapshot come from when an attacker’s website defaults to a defaced look ( blue), and the archive’s origin; see Figure 4. The adversary includes a future a script is responsible for constructing the page with the correct reference to a page-altering resource from the archive. Initially, this look ( red). When an archive removes that constructive script, referenced resource might not exist, making the attack dormant. the page remains defaced, as illustrated below. When the attacker decides to archive the missing resource, an archive-anachronism occurs, in which a new resource is used in an 1 2
Blue Sharks
older website snapshot. Using a resource from within the archive’s 3 origin means that attackers can bypass even the strictest CSPs 4 5 websites. An archive anachronism attack has three requirements: (1) Script execution and controllable URL rewriting. The attacker must be able to control the archive’s URL rewriting so that a snap- In the scenario where the constructive script is never executed shot of the attacker’s website can reference an archived resource (due to rewriting or blocking by the archive), the page remains in acting as a payload. A JavaScript file loaded as the source of a script the initial (defaced) state , represented by the blue color. tag in the final snapshot can be such a resource. 4.1.3 Server-side Cloaking. Attackers have many “signals” avail- (2) Guessable snapshot URL. The URL of newly archived resources able to distinguish between a regular user visit vs. a web archive must be predictable. In Figure 4, the attacker’s website refers to an crawler. Depending on the targeted web archives, attackers can external resource from the year 2050. Wayback Machine is known evade archive crawlers based on their IP address, autonomous sys- to utilize nearest-neighbor matching when given the timestamp of tem number, and identified browsing software. Using any of these a resource. For example, the path /web/2050//change.js vectors, attackers can serve archive crawlers content that differs may redirect to /web/20250325090111//change.js if that from that served to regular web users. Compared to the afore- is the most recent snapshot of the resource. mentioned attacks, this evasion is better concealed since there is (3) Retrievable resource content. Most web archives conduct some no evidence of alternative content saved in the page’s HTML or form of script rewriting when archiving a resource. Rewriting sub- JavaScript code for analysts to identify. Moreover, attackers can use resources would often interfere with correctly displaying the page server-side cloaking to deny a website’s archiving altogether. when replaying a recorded website. Thus, archives have (often The primary criterion for successful server-side evasions is the undocumented) ways to retrieve the “raw” resource without the ability to determine the nature of the current visitor in real-time. rewriting. In our example, where a script resource is loaded from a The Power to Never Be Wrong CCS ’25, October 13–17, 2025, Taipei, Taiwan Figure 4: Archive anachronism attack—future-reference to a Figure 5: Live-web escape attack—a snapshot breaks the resource inside another snapshot. archive’s boundaries to include a live-web resource. future snapshot, it is essential that script rewriting does not hinder the script’s functionality. To illustrate, the following HTML snippet combines these three techniques. to load resources from another origin, i.e., the live Web. Figure 5 illustrates a live-web escape where a script in a website’s snapshot 1 escapes the archive’s origin to load another script from the live web 2 Like archive anachronism, live-web escape requires script exe- cution. Code included in a website’s snapshot will run under the archive’s origin after archival. To affect the snapshot’s appearance, At the time of our study, Conifer executed code in onerror han- two cross-site scripting (XSS) capabilities are required: (1) External dlers, satisfying the first requirement for an archive anachronism requests. The code in the snapshot must be able to request a resource attack. The executed code dynamically creates a new script tag from from an attacker-controlled domain, which typically contains ad- a source within the archive. Here, snapshot URLs are guessable. ditional attacker code. (2) DOM manipulation. Second, to deface Namely, the URL includes a future timestamp, which the archive the snapshot, the attacker requires DOM manipulation capabilities. redirects to the nearest existing timestamp of that resource, satisfy- Depending on the adversary’s goals, they might want to apply a ing the second requirement. Finally, two additional techniques are wide range of DOM modifications, ranging from subtle changes to used to ensure Conifer returns a raw and executable version of the the content of an older snapshot to radically changing the look and referenced script. Appending the undocumented string js_ to the feel of the archived website. timestamp, combined with a .txt resource type, prompts the archive As a defense, a sufficiently restrictive Content-Security Policy to serve the raw script content. Once the page with this code is (CSP) can prevent code execution from third-party sources, as- rehosted under Conifer’s domain and the referenced resource be- suming attackers cannot somehow bypass the restrictive CSP. In comes available, i.e., after a save-page request for the payload URL, Section 5.2, we discuss the concrete defensive measures—including the referenced script can execute and change the snapshot. potential CSPs—of the archiving services. Payload updates. From an attacker’s perspective, a web archive ideally has a timestamp-matching feature that enables them to Attacks summary. Archive anachronism attacks execute resources update the appearance of an older snapshot at their discretion by from outside a snapshot’s original time period to alter a page’s ap- simply requesting the re-archiving of their payload resource. When pearance after it was captured. Depending on the exact variation the page’s snapshot is revisited, the visitor’s browser will follow of the attack, the attacker-controlled anachronistic resources either the reference, load the updated resource from the archive’s origin, come from within the archive’s origin or outside of it. In contrast to and execute it. Without such a mechanism, the payload itself can these attacks, archive-evasion attacks aim to prevent web archives alternatively include a forward reference to a following payload, from accurately archiving websites. effectively creating a chain of payloads. Either of these two methods would allow attackers to perform anachronistic attacks not just Key Takeaway 2. Attackers can modify their own archived once but an arbitrary number of times in the future. content long after archival—a novel and previously unheard-of Resource deletion attack. There is a theoretical variation of this attack vector. attack abusing an archive’s delete snapshot functionality. In re- verse order to the archive anachronism attack, a resource from the archive is initially used to control the look of a snapshot. The page 5 Results and Evaluation is built so that if that resource is not present, it defaults to a defaced In addition to the descriptive statistics produced from the metadata appearance. The attack involves requesting that the resource be collected during our experiment period (ref. §3.5), we analyzed the deleted at a later time, e.g., via the archive’s delete snapshot func- way each archiving service creates snapshots of pages to understand tionality. Upon fulfillment of that deletion request, the snapshot’s their vulnerability to evasions and anachronistic attacks (ref. §4). In appearance defaults to the defaced look (refer to Appendix A.1). this section, we describe the different defensive measures that web 4.2.2 Live-web Escape. In contrast to archive anachronism attacks, archives employ and present their vulnerability to our proposed live-web escapes completely overcome the archive’s boundaries archive attacks, despite these countermeasures. CCS ’25, October 13–17, 2025, Taipei, Taiwan Robin Kirchner, Chris Tsoukaladelis, Martin Johns, and Nick Nikiforakis ### Table 4: Overview of defensive measures in popular web archiving services | Archive measure | Wayback | Archive.Today | Perma.cc | Megalodon | Megalodon “snapshot-only” | Ghost Archive | ARQUIVO | FreezePage | Conifer | |---|---|---|---|---|---|---|---|---|---| | Root CSP | yes | no | no | no | no | no | no | no | yes | | Subdocument CSP | yes | no | yes | no | no | yes | no | no | no | | iframe | no | no | yes | yes | no | yes | yes | yes | yes | | iframe sandbox | no | no | no | yes | no | no | no | no | no | | Source Rewriting | yes | yes | yes | yes | yes | yes | yes | yes | yes | | Static URL Rewriting | yes | yes | yes | yes | yes | yes | yes | yes | yes | | Dynamic URL Rewriting | yes | no | yes | no | no | yes | yes | no | yes | | Unguessable IDs | no | no | yes | no | no | no | no | yes | no | | Script Execution Possible | indirectly possible | not possible | indirectly possible | not possible | directly possible | indirectly possible | indirectly possible | directly possible | indirectly possible | Legend: **directly possible** transcribes a black filled circle; **indirectly possible** transcribes a gray filled circle; **not possible** transcribes an open circle. The source's merged “no” cells for iframe and iframe sandbox are repeated in both rows for Wayback, Archive.Today, and Megalodon “snapshot-only”. 5.1 Demonstration We have produced detailed recordings of the attacks described in this paper and edited them into a single 36-minute-long video, which we uploaded to Vimeo. We prepared timestamped links for all successful attacks, with four examples in the table below. Timestamp Description Link 26:49 Conifer Archive Anachronism Vimeo 06:45 Wayback Machine Live-web Escape Vimeo 07:55 Archive.Today CSP Stripping Vimeo 20:53 Perma.cc Server-side Cloaking Vimeo The first two videos demonstrate our anachronistic attacks, Archive Anachronism and Live-web Escape for Conifer and the Way- back Machine, respectively. The remaining two videos show archive evasion attacks on Archive.Today via CSP stripping and Perma.cc via Server-side Cloaking. All links are available in Table 5. As the last row of Table 4 indicates, script execution is possible for all functionality-preserving archives despite their protective 5.2 Web Archive Defenses measures. FreezePage is the only service where code execution is Table 4 displays the defensive measures the web archiving services directly possible in HTML elements or attributes. Namely, Freeze- deploy. Megalodon stands out, as it underwent a series of secu- Page snapshots can execute code in onerror, onload, and onclick rity patches [4] in January and February 2025 during our study. event handlers. Before Megalodon’s patches introduced an iframe While the patches were effective, their application was incomplete. sandbox, script tags nested inside SVG tags could also execute Specifically, Megalodon offers a “snapshot-only” view5 , which can JavaScript code. The updates introduced an iframe sandbox around be accessed both through the menu and by modifying the URL. the recorded website. However, that security change was not ap- Placing /ref/ before the timestamp in the URL navigates directly to plied to the snapshot-only mode, which is still prone to XSS. With the snapshot-only mode. Megalodon’s website displays a toolbar, the exception of Archive.Today, attackers can execute JavaScript which is removed in snapshot-only mode. As both modes work in- code in all other archives by abusing a number of different blind terchangeably, we describe our results for the snapshot-only mode. spots and techniques. We discuss these vulnerabilities in the fol- A well-defined CSP can prevent the execution of unwanted code lowing sections. (typically as a defense against XSS), such as inline code or code from external origins. While this would be an effective defense against 5.3 Vulnerable Archives some of our anachronistic attacks, only the Wayback Machine and Table 5 shows which web archiving services are vulnerable to which Conifer deploy a CSP on their main website. Perma and Ghost of our proposed attacks. Archive have a subdocument CSP, which only applies to an iframe Key Takeaway 3. Despite the archives’ claims to provide exact that embeds the recorded snapshot. HTML5’s iframe sandboxes in- and unchangeable snapshots, all archiving services we investi- troduced security restrictions and isolation to framed content. Only gated were vulnerable to at least one group of attacks. Megalodon puts the embedded snapshot in a sandbox so that code execution is effectively prevented. All archives conduct some form of static server-side content rewriting when moving a website into 5.3.1 Evaluation of Anachronistic Attacks. We found vulnerabilities the archive’s domain. We observed the use of libraries like Wom- to anachronistic attacks for seven archiving services. Archive.Today bat [58] or pywb [57] to rewrite URLs used in the original website is the only service immune to this attack, as no code execution is and rehost resources inside the archive. Furthermore, five services possible in snapshots. Note that Megalodon hardened its service (Wayback, Perma, Ghost Archive, and Conifer) use mechanisms against script execution after we recorded our proof of concept. that dynamically intercept requests. This can be done by either In the most recent version of Megalodon, one has to visit evasive patching JavaScript networking APIs like fetch or XMLHttpRequest snapshots in snapshot-only mode to see the effects of the attack. to redirect requests or by registering service workers for the same The first group of attacks, archive anachronism, requires deter- task. Archive.Today uses the fewest client-side defenses. However, mining the URL a resource will receive after archiving (ref. §4.2.1). the service strips websites of virtually all dynamic content. It only Wayback Machine, ARQUIVO, Archive.Today, and Conifer have preserves the page’s static content while stripping the page of any nearest-neighbor timestamp matching mechanisms that redirect a executable elements. This approach works well to preserve static snapshot URL with a nonexistent timestamp to the snapshot clos- web content like articles or blogs, but it is unqualified to capture a est to the indicated time. In contrast, Archive.Today6 and Ghost website’s behavior. Archive7 appear to use unguessable alphanumeric snapshot IDs. Guessable snapshot URLs are a key requirement for archive Still, both services also offer alternative URL formats. In the pres- anachronism attacks (ref. §4.2.1). As indicated in the second-to-last ence of a matching mechanism, guessing the snapshot URL of row, most archives use guessable timestamped URLs for snapshots. 6 Archive.Today has interchangeable timestamped URLs and short URLs. 5 7 魚拓のみの表示” translated as “snapshot-only” or “web capture-only” view. Ghostarchive has a /longurl/ API endpoint converting short to timestamped URLs. The Power to Never Be Wrong CCS ’25, October 13–17, 2025, Taipei, Taiwan Table 5: Overview of the vulnerability of Web archiving ser- Table 6: Initial XSS vectors to achieve external requests and vices to our attacks, with links to attack demos . DOM manipulation in archives vulnerable to live-web escape. Anachronistic Archive Evasion Attacks Script execution for external requests & DOM manipulations via Attacks Server-side Cloaking Vulnerable Script Event SVG iframe (same-origin, Anachronism User-Agent Archives elements handlers with script no CSP) JA3 / JA4 IP / ASN Stripping Stripping Live-web Archive Escape Script CSP Archive Name Wayback Machine no no no yes Perma.cc no no no yes Megalodon no no yes1 no Wayback Machine yes yes yes no yes yes1 no3 Ghost Archive no no no yes Archive.Today no no yes no no2 yes no ARQUIVO no no no yes Perma.cc no yes yes no yes yes no FreezePage no yes no no Megalodon yes4 yes4 yes no yes yes no Conifer no no no yes Ghost Archive yes yes yes no yes yes no 1 Code execution is only possible in Megalodon’s “snapshot-only” mode. ARQUIVO yes yes yes no yes yes no3 FreezePage no yes yes yes yes yes no Conifer yes yes yes no yes yes no 1 Wayback’s JA3’s are too numerous for effective detection, but JA4 is suitable. we used to achieve external requests and DOM manipulation for 2 Detecting Archive.Today’s crawlers effectively requires extensive observation to the archives vulnerable to live-web escapes in Table 6. gather sufficient network-level information. Freezepage does not sufficiently sanitize event handlers, making 3 User agents that mention the archive’s crawler can be exploited for evasion. 4 live-web escape attacks easy using one-line exploits in onload or The attack works only in Megalodon’s “snapshot-only” mode. onerror attributes of images. Megalodon snapshots pre-patch and a resource before archiving it is as easy as specifying a future post-patch in snapshot-only mode can leak into the live web and timestamp, e.g., https://arquivo.pt/wayback/20500000000000/, change themselves through a script nested in an SVG. The remain- which automatically redirects to the snapshot closest to the year ing vulnerable archives require multi-step exploits. The first step 2050. This makes snapshot URLs guessable and human-readable. of our client-side attacks is dynamically creating an iframe sourced We achieve a similar effect for Megalodon by programmatically from a subpage of the archive that does not have a CSP, such as querying its search API and extracting the newest snapshot of the an error page. As a result, this iframe satisfies the SOP because desired anachronism-resource URL via JavaScript. Extracting the it is from the same origin as the archive and is not subject to a unchanged anachronism resource from a snapshot is the second CSP. The second step entails creating a script that fetches a remote requirement. Most archiving services have (undocumented) me- resource in that iframe. If needed, the external URL can be Base64 chanics in their URL, which cause the archive’s server to respond encoded to evade rewriting. The fetch-response is then used to with the raw resource. For example, Wayback, ARQUIVO, and rewrite the iframe’s parent document, the snapshot. Depending on Conifer deliver raw resources when “js_” is inserted after the times- the archive, different vectors were used to create a dynamic code- tamp of a snapshot URL. In the case of Ghost Archive, we pierce executing iframe. Specifically, scripts in SVG elements (Perma.cc, multiple shadow DOMs with chained query selectors to retrieve the Ghost Archive, ARQUIVO), onerror handlers (Perma.cc, Freeze- archived resource from a snapshot. We found that satisfying the last Page), or simple scripts (Wayback Machine, Conifer) were used. requirement—controlling URL rewriting—is often straightforward, for example, by dynamically writing URLs through string concate- 5.3.2 Evaluation of Archive Evasion and Snapshot Prevention. Sup- nation or by encoding and decoding them in Base64 (potentially pose the most impactful attacks, the anachronistic attacks, are im- multiple times) as illustrated in lines 1 and 2 below. possible for an archive, which applies to all web archives that are strictly content-only. If a service is immune to anachronistic attacks, 1 iframe.src = 'https://' + 'archive.org' + '/error-page'; adversaries can still attempt to launch archive-evasion attacks. As 2 fetch(atob(atob(atob('WVVoU01HTklUVFpNZVRsMldXNU9iR051V21oa1J6bDVaVk0xTUZwWVR ↪ qQk1NMVozV2tkR01GcFJQVDA9'))).then(/* use response */) described in Section 4.1, in these attacks, adversaries can either stop the service from archiving their content or serve the archiving Despite our efforts, we could not identify a method for guessing service content that is different than what regular web users would the URL a resource will receive when archived in FreezePage and be served. In this section, we evaluate the effectiveness of evasion Perma.cc, respectively. In other words, the services use a hard-to- attacks. Refer to the right side of Table 5. guess URL format and do not offer a search function. Thus, force- CSP Stripping. As all web archives we tested opt not to adopt fully including intra-archive resources in FreezePage and Perma the CSP of the pages they snapshot, they are vulnerable to our CSP snapshots is more complex than escaping the archives’ boundaries stripping attack. FreezePage replaces script tags, which makes CSP and injecting a live-web resource, which we discuss next. directives like script-src ineffective. Since event handlers run on Leaking into the live-Web. Contrary to expectations, all function- FreezePage, the same effect can be recreated using event handlers ality-preserving archives are vulnerable to live-web escape, our that the attacker’s website disabled with the script-src-attr=’none’ most potent attack. Only sandboxed Megalodon snapshots and CSP directive. The attacker’s website now effectively disallows Archive.Today recordings sufficiently prevent code execution that scripts in HTML element attributes, including onerror event han- could lead to archive escapes. As previously mentioned, external dlers. When FreezePage—and the other archives—strip the CSP, the requests to fetch updated content and the ability to manipulate the event handler—or scripts—run, respectively, and deface the page. DOM to alter the snapshot are prerequisites for a successful live- Overall, CSP stripping is a convenient attack that allows defining web escape attack (ref. §4.2.2). We present the specific XSS vectors code that is only executed in the context of web archives. CCS ’25, October 13–17, 2025, Taipei, Taiwan Robin Kirchner, Chris Tsoukaladelis, Martin Johns, and Nick Nikiforakis Script Stripping. This attack variation is only effective for Freeze- 1996. Stock et al. [52] used the Wayback Machine to conclude that Page, which makes it less usable as a generic archive-evasion tech- websites were vulnerable to a novel class of XSS eight years be- nique. Script stripping works because FreezePage rehosts pages fore the vulnerability was first mentioned. Using web-archive data, with script tags replaced by custom non-executing Amos et al. [7] compared privacy policies over time, Iqbal et al. [27] tags. Note that while Megalodon and Archive.Today disable scripts, studied the evolution of ad-blocker filter lists, and Scheitle et al. [49] they do so only after executing them on the server side when creat- investigated the stability of top website lists used in web-related ing a snapshot. The archives then freeze how the DOM looks after research studies. Recently, Hantke et al. [21] studied security mea- the page has finished loading in the presence of the script. surements using snapshots as an alternative to conventional live measurements. These works highlight the importance of creating Server-side evasion. While CSP Stripping proved a convenient detailed and unchangeable snapshots of websites over time. technique for the evasive adversary to control how a website looks Other works show the challenging process of investigating the when any service rehosts it, the attack does not differentiate be- inner workings of web archives. Ogden et al. [44] conducted a pilot tween different archives. The anachronistic adversary wants to study on how the “Save Page Now” feature of the Internet Archive allow deceivable archives to record their website while prevent- creates snapshots of websites, finding its inner workings largely ing archival in specific content-only archives. Server-side evasion opaque. The observatory that we presented in this paper allowed offers individual control at the cost of requiring characteristic in- us to shed light on the “invisible” parts (i.e., the crawlers dispatched formation about the different archiving services. Such information to archive one’s website) of popular web archiving services. has to be acquired through an observatory, like ours (ref. §3). Ainsworth et al. [5] were the first to notice incidental discrep- Table 5 displays which information can be effectively used to ancies between the live Web and the archived Web, showcasing detect the archive crawlers of the eight evaluated archiving ser- the limitations of current archives. After finding accidental archive vices. We differentiate between information about IP addresses, TLS escapes into the live web [36], Lerner et al. [35] were the first to fingerprints, and User-Agent information from HTTP headers. The write about security issues in the Wayback Machine that can lead most broadly usable crawler characteristic is its IP address and AS to changing past records. The authors found that faulty URL rewrit- number. While the archive crawlers, except for Archive.Today’s, ing can lead to accidental leaks of live web content into snapshots. use only one AS (ref. Table 2), most are situated on large net- Additionally, subresources that initially fail to archive can later works and cloud providers, making them unusable for targeted IP be added by attackers. Both flaws can be abused to alter archived blocking. Wayback Machine is an exception as its ASN INTERNET- snapshots retrospectively. Follow-up work by Watanabe et al. [56] ARCHIVE (7941) simplifies detecting the service. Similarly, Freeze- focuses on the security implications of the SOP when web services Page, Ghostarchive, and Conifer use a single IP address for their rehost websites under one domain. They propose various attacks, crawler, making them immediately identifiable. Multiple websites including a persistent Man-in-the-middle where an evil.js script the must be archived to detect the remaining IP addresses of the other SOP would normally block is allowed to execute once it is brought services. We observed a stable set of three IP addresses for Perma.cc under the archive’s domain, as well as privilege abuse attacks aim- and Meghalodon after three archiving requests, a second IP for ing at accessing a user’s camera or other hardware, and attacks that ARQUIVO after five requests, and 19 IP addresses for Wayback’s steal user credentials or browser history. crawlers after 21 archived pages (ref. Figure 2). Archive.Today is The study by Lerner et al. motivated our work [35]. The key rotating its crawlers’ IPs and ASNs, making the detection of their difference is that we propose entirely new threat models and corre- crawlers prone to errors. sponding attacks based on them. Instead of third-party attackers We discovered that TLS fingerprints qualify for archive crawler identifying and abusing live-web leaks in third-party sites, we in- detection. Figure 2 displays the unique TLS fingerprints we recorded vestigated attackers who want to stop or control the archiving of for the archiving crawlers that visited our observatory. Wayback their websites. These attackers have complete control over their Machine’s rotation of cipher suits (ref. §3.5) creates a myriad of own websites and can, therefore, include code and data that abuses JA3 fingerprints, three orders of magnitude higher than the other all exploitable corner cases of each archive’s logic. The work by archives after our 195 archiving requests. JA4 provides a much more Watanabe et al. [56] mainly focuses on web rehosting in general, manageable amount of archiving crawler TLS fingerprints after and the attacks discussed were purely theoretical. Our practical one to 25 archiving requests, depending on the archiving service. attacks and focus on web archiving services allow us to pinpoint Overall, the combination of IP address, ASN, and JA4 reliably reveals the shortcomings of the web archiving ecosystem more accurately. all archive crawlers and can, therefore, be used by attackers for server-side evasions. Due to its distributed network infrastructure, Archive.Today is more challenging to detect. 7 Discussion All web archives aim to truthfully preserve past content, as stated 6 Related Work in their mission statements. Content-only archives take a security- Prior work recognizes web archiving services, particularly the Inter- first approach, sacrificing interactivity for simplicity and increased net Archive’s Wayback Machine, as important tools for longitudinal, security. Functionality-preserving archives, however, document reproducible, and retrospective web research. Nikiforakis et al. [43] technical properties of past web applications, which is essential utilized snapshots of websites to research trends in JavaScript in- for research on historical web security and code analysis. Achiev- clusion from 2001 to 2010 [43]. Lerner et al. [36] retrospectively ing these goals securely is challenging, as preserving client-side analyzed the evolution of third-party web tracking behaviors from functionality can introduce vulnerabilities. The Power to Never Be Wrong CCS ’25, October 13–17, 2025, Taipei, Taiwan Our study identified multiple security measures implemented Unguessable snapshot URLs are required to prevent anachro- by archives (ref. §5.2), all of which we were able to circumvent in nistic attacks. These attacks depend on the ability to predict and archives that permitted script execution (ref. §5.3). Some archives at- prematurely reference future archive URLs. While adopting an tempted to mitigate risks through sandboxing mechanisms, such as unguessable URL scheme is straightforward for future captures, iframe restrictions and CSPs, to prevent XSS. However, inconsistent retroactively rewriting existing URLs remains challenging. use of CSP on subpages of the archives reduced its effectiveness. To mitigate server-side evasion attacks, employing a diverse set We also observed characteristics that make server-side detection of crawlers, ideally distributed across multiple autonomous systems, of archive crawlers challenging. Archive.Today stands out with its can significantly impede detection and blocking by live websites. diverse infrastructure encompassing the largest number of IP ad- dresses and ASNs. The service also uses various user agent strings 7.2 Disclosure and Ethical Considerations mimicking real browsers. However, TLS fingerprinting allows de- We contacted all archiving services via email in early April 2025. tection of their crawlers. The variable TLS client configurations Seven of the eight services responded and requested full details. that the Wayback Machine employs were unexpected and resulted Three services—Perma.cc, the Internet Archive, and Archive.Today— in a large number of TLS fingerprints. Nevertheless, the service followed up with additional discussions about possible mitigations. uses only one specific ASN, making the service immediately recog- Our findings have already led to a real-world impact. The In- nizable to malicious web servers. ternet Archive and Archive.Today acknowledged our findings and are engaging with us directly. Perma.cc has already rolled out a Implications of our findings. We have shown that the crawlers of all series of targeted patches in response to our CSP escape attacks [e.g. archives can be effectively detected with a few weeks’ worth of data. 31–33] and shared their full internal incident report with us. Our This capability, combined with the more impactful anachronistic discussions with the archives and the evident dedication to urgently attacks we were able to execute on all script-executing archives, addressing the issue we brought to light underscore that the archiv- creates the biggest threat to the archives’ main goal: faithful rep- ing services take our findings seriously. Interested readers can refer resentation of past websites. An evasive adversary can focus on to Appendix A.2 for further details on the disclosure process. individual vulnerable archives and evade archival by all others they cannot exploit. This forces potential readers of the adversary’s Ethical Considerations. For the observatory study, we archived only pages’ snapshots to use archives that the adversary can control. The our own websites and maintained detailed records of the archived takeaway message is that, in light of these attacks, web archives URLs, in case any archive required deletion. To reduce strain on the cannot be fully trusted since adversaries can change the content of archiving services, we stretched out the experiments over 16 days their snapshots. Even though some of our attacks have a client-side and artificially limited our study to approximately one archival footprint (e.g., live-web leaks and anachronistic attacks referencing request per hour. This work focuses on attacks enabled by fun- future archived resources), these footprints are invisible to regular damental design choices and technical limitations of current web users of the archive and would be hard to identify even for experts archiving services. Our goal is to ultimately improve the archives’ who are capable of analyzing the DOM of an archived page. robustness against evasion and anachronistic manipulation. Due to ethical considerations, attacks against the servers of web archiving Limitations and Future Work. False positives are possible when an services were entirely out of scope. evasive adversary attempts to identify web-archive crawlers based on client characteristics. Our observatory does not aim to be a plug- 8 Conclusion in solution to block archive crawlers, but rather the first attempt In this work, we studied the intrinsic characteristics of eight of the to understand the “invisible” server-side infrastructure that these most popular web archiving services and showed that we can detect services operate and to what extent attackers can evade or abuse their archiving crawlers. We have proposed five attacks against this infrastructure. A concrete future direction is designing a web web archives that an evasive, anachronistic publisher can leverage archive service that is hardened against our identified server-side to control what archives store about their online presence. Combin- and client-side attacks without compromising on the functionality ing powerful anachronistic attacks against specific services with of the archived websites. Additionally, access-control mechanisms archive evasion attacks against the others ultimately creates “the for web archives are a promising future direction where websites power to never be wrong,” as adversaries can arbitrarily change their can transparently opt out of being archived (as opposed to trying to past archived content. To our knowledge, we are the first to move detect and evade web archiving services). Our work can hopefully from accidental vulnerabilities in snapshots to exploring evasion encourage more research in that direction. channels that attackers can intentionally create on their websites. We demonstrated that all in-scope web archives are vulnerable to 7.1 Securing Existing Web Archives one or more of our attacks, enabling us to control what content the Gaps in CSP coverage and insufficient code rewriting were the most services can archive. For anachronistic attacks, we retained control common factors enabling our client-side attacks. When rewriting a over past snapshots for seven of the eight archiving services. website’s code, future archives must account for obfuscation tech- Faithfully archiving yesterday’s Web is essential for the preser- niques such as string concatenation and Base64 encoding. Addi- vation of historical information and to enable web security research. tionally, since the Same-Origin Policy permits interactions between Our findings will help harden web archiving services against inten- pages with and without CSP, a consistent CSP must be present tional server-side and client-side attacks that impact their primary across all subpages of a web archiving service. goal of truthfully preserving the past. CCS ’25, October 13–17, 2025, Taipei, Taiwan Robin Kirchner, Chris Tsoukaladelis, Martin Johns, and Nick Nikiforakis Availability. We have recorded extensive demos for all presented [20] Alejandro Gómez-Boix, Pierre Laperdrix, and Benoit Baudry. 2018. Hiding in attacks against all services and made them available in Section 5.1. the Crowd: An Analysis of the Effectiveness of Browser Fingerprinting at Large Scale. In Proc. of the World Wide Web Conference. ACM Press, 309–318. Our archive observatory implementation is publicly available on [21] Florian Hantke, Stefano Calzavara, Moritz Wilhelm, Alvise Rabitti, and Ben Stock. Zenodo8 and GitHub9 . We will only share the collected data on web 2023. You Call This Archaeology? Evaluating Web Archives for Reproducible Web Security Measurements. In Proceedings of the 2023 ACM SIGSAC Conference archive crawlers with bona fide, established researchers to prevent on Computer and Communications Security. ACM. misuse. [22] James L. Quarles III and Richard A. Crudo. 2014. WayBack to the Future: Using the Wayback Machine in Patent Litigation. https://web.archive.org/web/ 20241114043112/https://www.americanbar.org/groups/intellectual_property_ Acknowledgments law/publications/landslide/2013-14/january-february/wayback-future/. [23] Internet Archive. 2025. Internet Archive: Digital Library of Free & Borrowable We thank our shepherd and the anonymous reviewers for their Texts, Movies, Music & Wayback Machine. https://archive.org/. Accessed: valuable comments and suggestions. We gratefully acknowledge 2025-01-11. [24] Internet Archive. 2025. InternetArchiveBot: A Wikipedia bot that fights. https: funding by the Deutsche Forschungsgemeinschaft (DFG, German //github.com/internetarchive/internetarchivebot. Accessed: 2025-01-11. Research Foundation) under Germany’s Excellence Strategy – EXC [25] Internet Archive. 2025. Wayback Machine. Online https://web.archive.org/. 2092 CASA – 390781972. This work was also supported by the Army (2025-03-27). [26] Luca Invernizzi, Kurt Thomas, Alexandros Kapravelos, Oxana Comanescu, Jean- Research Office (ARO) under grant W911NF-24-1-0051 as well as Michel Picod, and Elie Bursztein. 2016. Cloak of visibility: Detecting when the National Science Foundation (NSF) under grants CNS-1941617 machines browse a different web. In 2016 IEEE Symposium on Security and Privacy and CNS-2126654. (SP). IEEE, 743–758. [27] Umar Iqbal, Zubair Shafiq, and Zhiyun Qian. 2017. The ad wars: retrospective measurement and analysis of anti-adblock filter lists. In Proceedings of the 2017 References Internet Measurement Conference. 171–183. [28] Dana Kennedy. 2022. Washington Post issues two corrections to Taylor Lorenz [1] Lawrence Abrams. 2024. Internet Archive hacked, data breach impacts article that had already been stealth-edited . https://web.archive.org/web/ 31 million users. https://web.archive.org/web/20250630153136/https: 20250331023742/https://nypost.com/2022/06/04/washington-post-adds-two- //www.bleepingcomputer.com/news/security/internet-archive-hacked- corrections-to-taylor-lorenz-piece/. data-breach-impacts-31-million-users/. (2025-06-30). [29] Brian Kondracki, Johnny So, and Nick Nikiforakis. 2022. Uninvited Guests: Ana- [2] Abstract. 2025. IP Geolocation API. Online https://www.abstractapi.com/api/ip- lyzing the Identity and Behavior of Certificate Transparency Bots. In Proceedings geolocation-api. (2025-03-24). of USENIX Security Symposium (USENIX Security). [3] Aaron M Adams, Xiang Chen, Weidong Li, and Chuanrong Zhang. 2023. Nor- [30] Martijn Koster, Gary Illyes, Henner Zeller, and Lizzi Sassman. 2022. Robots malizing the pandemic: exploring the cartographic issues in state government Exclusion Protocol. RFC 9309. https://datatracker.ietf.org/doc/html/rfc9309 COVID-19 dashboards. Journal of Maps 19, 1 (2023), 1–9. [31] Kreymer, Ilya. 2025. GitHub: wabac.js—Pull Request #243. Online https://github. [4] Affility Co.,Ltd. 2025. 株式会社アフィリティー. Online https://www.affility. com/webrecorder/wabac.js/pull/243. (2025-07-03). co.jp/. (2025-03-26). [32] Kreymer, Ilya. 2025. GitHub: wabac.js—Pull Request #245. Online https://github. [5] Scott G. Ainsworth, Michael L. Nelson, and Herbert Van De Sompel. 2015. Only com/webrecorder/wabac.js/pull/245. (2025-07-03). One Out of Five Archived Web Pages Existed as Presented. In Proceedings of the [33] Kreymer, Ilya. 2025. GitHub: wabac.js—Pull Request #246. Online https://github. 26th ACM Conference on Hypertext & Social Media - HT ’15. ACM Press. com/webrecorder/wabac.js/pull/246. (2025-07-03). [6] John Althouse. 2025. TLS Fingerprinting with JA3 and JA3S. On- [34] Victor Le Pochat, Tom Van Goethem, Samaneh Tajalizadehkhoob, Maciej Kor- line https://web.archive.org/web/20250323120934/https://engineering.salesforce. czyński, and Wouter Joosen. 2019. Tranco: A research-oriented top sites ranking com/tls-fingerprinting-with-ja3-and-ja3s-247362855967/. visited (2025-03-24). hardened against manipulation. In 26th annual network and distributed system [7] Ryan Amos, Gunes Acar, Eli Lucherini, Mihir Kshirsagar, Arvind Narayanan, and security symposium (NDSS ’19). doi:10.14722/ndss.2019.23386 Jonathan Mayer. 2021. Privacy policies over time: Curation and analysis of a [35] Ada Lerner, Tadayoshi Kohno, and Franziska Roesner. 2017. Rewriting History: million-document dataset. In Proceedings of the Web Conference 2021. 2165–2176. Changing the Archived Web from the Present. In Proceedings of the 2017 ACM [8] Adam Barth. 2011. The Web Origin Concept. RFC 6454. doi:10.17487/RFC6454 SIGSAC Conference on Computer and Communications Security. ACM. [9] Bit Flip LLC. 2025. Dark Visitors: Bytespider. Online https://darkvisitors.com/ [36] Ada Lerner, Anna Kornfeld Simpson, Tadayoshi Kohno, and Franziska Roesner. agents/bytespider/. (2025-03-28). 2016. Internet Jones and the Raiders of the Lost Trackers: An Archaeological [10] Cloudflare. 2025. JA3/JA4 fingerprint. Online https://developers.cloudflare.com/ Study of Web Tracking from 1996 to 2016. In Proceedings of the USENIX Security bots/concepts/ja3-ja4-fingerprint/. visited (2025-03-24). Symposium. [11] Software Freedom Conservancy. 2025. Selenium. Online https://www.selenium. [37] Raizel Liebler and June Liebert. 2012. Something Rotten in the State of Legal dev/. (2025-03-19). Citation: The Life Span of a United States Supreme Court Citation Containing an [12] Dennis Fetterly, Mark Manasse, Marc Najork, and Janet Wiener. 2003. A large- Internet Link (1996-2010). Yale JL & Tech. 15 (2012), 273. scale study of the evolution of web pages. In Proceedings of the 12th international [38] Meng Luo, Pierre Laperdrix, Nima Honarmand, and Nick Nikiforakis. 2019. Time conference on World Wide Web. 669–678. Does Not Heal All Wounds: A Longitudinal Analysis of Security-Mechanism [13] FingerprintJS, Inc. 2025. GitHub: fingerprintjs. Online https://github.com/ Support in Mobile Browsers. In Proceedings of the 26th Network and Distributed fingerprintjs/fingerprintjs. (2025-03-19). System Security Symposium (NDSS). [14] FoxIO-LLC. 2025. GitHub: ja4. Online https://github.com/FoxIO-LLC/ja4. visited [39] Majestic. 2025. About MJ12Bot. Online https://www.mj12bot.com/. (2025-03-28). (2025-03-24). [40] John Markwell and David W Brooks. 2003. “Link rot” limits the usefulness of web- [15] Chris Freeland. 2024. Internet Archive Services Update: 2024-10-21. https: based educational materials in biochemistry and molecular biology. Biochemistry //blog.archive.org/2024/10/21/internet-archive-services-update-2024-10-21/. and Molecular Biology Education 31, 1 (2003), 69–72. [16] FreezePage. 2025. Freeze Any Web Page. Online https://www.freezepage.com/. [41] Ryan Mills. 2021. USA Today Let Stacey Abrams Stealth Edit Op-Ed to Downplay (2025-03-27). Support for Georgia Boycotts. https://web.archive.org/web/20240603035109/ [17] Ghostarchive. 2025. Ghostarchive, a website archive. Online https://ghostarchive. https://www.yahoo.com/news/usa-today-let-stacey-abrams-161435000.html. org/. (2025-03-27). [42] monperrus. 2025. GitHub: crawler-user-agents. Online https://github.com/ [18] Dion Hoe-Lian Goh and Peng Kin Ng. 2007. Link decay in leading information monperrus/crawler-user-agents/tree/283a9df01b. (2025-03-16). science journals. Journal of the American Society for Information Science and [43] Nick Nikiforakis, Luca Invernizzi, Alexandros Kapravelos, Steven Van Acker, Technology 58, 1 (2007), 15–24. Wouter Joosen, Christopher Kruegel, Frank Piessens, and Giovanni Vigna. 2012. [19] C. Douglas Golden. 2022. NYT Makes Stealth Edits to Elon Musk Piece Tainting You Are What You Include: Large-scale Evaluation of Remote JavaScript Inclu- Him with Apartheid Smears Writer Lashes Out at Critics. https://web.archive. sions. In Proceedings of the ACM Conference on Computer and Communications org/web/20250717060102/https://www.westernjournal.com/nyt-makes-stealth- Security (CCS). 736–747. edits-elon-musk-piece-tainting-apartheid-smears-writer-lashes-critics/. [44] Jessica Ogden, Edward Summers, and Shawn Walker. 2024. Know(Ing) Infras- tructure: The Wayback Machine as Object and Instrument of Digital Research. Convergence: The International Journal of Research into New Media Technologies 1 (2024). 8 Zenodo https://zenodo.org/records/17190361 [45] Perma.cc. 2025. “Websites change. Perma Links don’t.”. Online https://web. 9 GitHub https://github.com/robinki/archive-observatory archive.org/web/20250316210209/https://perma.cc/. (2025-03-26). The Power to Never Be Wrong CCS ’25, October 13–17, 2025, Taipei, Taiwan [46] Stijn Pletinckx, Thanh-Dat Nguyen, Tobias Fiebig, Christopher Kruegel, and Giovanni Vigna. 2023. Certifiably vulnerable: Using certificate transparency logs for target reconnaissance. In 2023 IEEE 8th European Symposium on Security and Privacy (EuroS&P). IEEE, 817–831. [47] Sebastian Roth, Timothy Barron, Stefano Calzavara, Nick Nikiforakis, and Ben Stock. 2020. Complex Security Policy? A Longitudinal Analysis of Deployed Content Security Policies.. In NDSS 2020. [48] salesforce. 2025. GitHub: ja3. Online https://github.com/salesforce/ja3. visited (2025-03-24). [49] Quirin Scheitle, Oliver Hohlfeld, Julien Gamba, Jonas Jelten, Torsten Zimmer- mann, Stephen D Strowes, and Narseo Vallina-Rodriguez. 2018. A long way to the top: Significance, structure, and stability of internet top lists. In Proceedings of the Internet Measurement Conference 2018. 478–493. Figure 6: Client-side cloaking by deleting an already archived [50] Singer, Ethan. 2025. New York Times: Thousands of U.S. Government Web subresource. Pages Have Been Taken Down Since Friday. Online https://archive.is/R8iq0. (2025-07-03). [51] StatCounter. 2019. Browser Market Share Worldwide. Online: http://gs. full manuscript of our work. All except one have acknowledged our statcounter.com/browser-market-share. findings and requested further details. Three services—Perma.cc, [52] Ben Stock, Martin Johns, Marius Steffens, and Michael Backes. 2017. How the the Internet Archive, and Archive.Today—followed up with addi- Web Tangled Itself: Uncovering the History of Client-Side Web (In)Security. In 26th USENIX Security Symposium (Usenix Sec’17). tional discussions about possible mitigations. Please find a detailed [53] Chris Tsoukaladelis, Brian Kondracki, Niranjan Balasubramanian, and Nick Niki- timeline of our disclosure process below. forakis. 2024. The Times They Are A-Changin’: Characterizing Post-Publication Changes to Online News. In Proceedings of the IEEE Symposium on Security and ● April 11, 2025 We reached out to all studied web archiving services, Privacy (IEEE S&P). describing who we are, giving a high-level overview of our goals [54] ultrafunkamsterdam. 2025. GitHub: undetected-chromedriver. Online https: //github.com/ultrafunkamsterdam/undetected-chromedriver. (2025-03-19). and findings, and requesting permission to share the full results [55] David Y Wang, Stefan Savage, and Geoffrey M Voelker. 2011. Cloak and dagger: with them. We received positive answers, i.e., the wish to receive dynamics of web search cloaking. In Proceedings of the 18th ACM conference on our findings, from everyone except Megalodon.jp, which never Computer and communications security. 477–490. [56] Takuya Watanabe, Eitaro Shioji, Mitsuaki Akiyama, and Tatsuya Mori. 2020. responded to our email. Melting Pot of Origins: Compromising the Intermediary Web Services That ● April 15, 2025 We finalized the manuscript and submitted this Rehost Websites. In Proceedings 2020 Network and Distributed System Security paper to CCS. To the services that had positively responded to Symposium. Internet Society. [57] webrecorder. 2025. GitHub: pywb 2.8. Online https://github.com/webrecorder/ our initial email, we sent full details of the attacks described in pywb. (2025-03-26). this paper, along with an explanation of how each service was [58] webrecorder. 2025. GitHub: Wombat. Online https://github.com/webrecorder/ wombat. (2025-03-26). susceptible. [59] Mike West and Antonio Sartori. 2025. Content Security Policy Level 3. W3C ● April 15, 2025 Archive.Today and Perma.cc responded on the same Working Draft. W3C. https://www.w3.org/TR/2025/WD-CSP3-20250206/. day, thanking us for our report, providing some early feedback [60] Wikipedia. 2025. Wikipedia:Link rot. https://en.wikipedia.org/wiki/Wikipedia: Link_rot. Accessed: 2025-01-11. (in the case of Archive.Today) on why they do what they do, and [61] Savvas Zannettou, Jeremy Blackburn, Emiliano De Cristofaro, Michael Sirivianos, promising to follow up with more information. and Gianluca Stringhini. 2018. Understanding web archiving services and their ● April 24, 2025 We received another answer from Perma.cc. They (mis) use on social media. In Proceedings of the International AAAI Conference on Web and Social Media, Vol. 12. considered the issue of server-side archive evasions to be “hard to [62] Penghui Zhang, Adam Oest, Haehyun Cho, Zhibo Sun, RC Johnson, Brad Ward- avoid.” They requested more information on the live-leak attacks, man, Shaown Sarker, Alexandros Kapravelos, Tiffany Bao, Ruoyu Wang, et al. 2021. Crawlphish: Large-scale analysis of client-side cloaking techniques in which they felt should be patched. phishing. In 2021 IEEE Symposium on Security and Privacy (SP). IEEE, 1109–1124. ● April 25, 2025 Our team sent Perma.cc additional information, [63] Ke Zhou, Claire Grover, Martin Klein, and Richard Tobin. 2015. No more 404s: including code snippets and a proof-of-concept that they could predicting referenced link rot in scholarly articles for pro-active archiving. In Proceedings of the 15th ACM/IEEE-CS Joint Conference on Digital Libraries. 233– use to recreate our live-leak attacks. 236. ● April 30, 2025 We received an email with an extended response [64] Jonathan Zittrain, Kendra Albert, and Lawrence Lessig. 2014. Perma: Scoping from Perma.cc describing how they addressed our live-leak at- and addressing the problem of link and reference rot in legal citations. Legal Information Management 14, 2 (2014), 88–99. tacks. Their response included substantial technical details and forensic information, including reasons for why they were vulner- able in the first place. They pointed us to patches on GitHub [31, A Appendix 32] that were pushed as a result of our reports and asked if we A.1 Theoretical Attacks had discovered additional attacks beyond the ones described in Delete Snapshot is a theoretical variation of the archive anachronism our paper (we had not). attack in reverse order. The attacker built their website to use ● May 14, 2025 Given the prominence of the Internet Archive, we a resource from the archive to control the look of the website’s followed up on our email by sending them our findings to inquire snapshot, as displayed in Figure 6. The page defaults to a defaced whether they had a chance to review it. On the same day, we appearance when the resource is not present. They request that the received a response from the Internet Archive letting us know resource be deleted via the archive’s delete-snapshot functionality that they were still considering out findings and inquiring as to to deface the snapshot at a time of the attacker’s choice. the eventual publication date of this paper. A.2 Disclosure Details We contacted each concerned archiving service in early April 2025 via email, informing them about our study and offering them the