---
type: Whitepaper
title: "State of the Art: Automated Black-Box Web Application Vulnerability Testing"
description: Eight commercial black-box web scanners were run against Drupal, phpBB2 and WordPress builds with known bugs and against a purpose-built testbed of ~90 verified vulnerabilities. Reflected XSS was found at over 60%, but stored XSS reached only 15% and no scanner found any second-order SQL injection or planted malware. Scanners also failed to follow links inside Java, Flash and Silverlight.
resource: "https://web.stanford.edu/~jcm/papers/pci_oakland10.pdf"
tags: [whitepaper, webseclist-reference, measurement-study, tooling, detection, xss, sqli, csrf, info-leak, large-scale-scan, dynamic-analysis, owasp-a01-2021, owasp-a03-2021, owasp-a09-2021]
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  at: "2026-08-14T22:35:59+00:00"
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    resource: "https://web.stanford.edu/~jcm/papers/pci_oakland10.pdf"
    title: "State of the Art: Automated Black-Box Web Application Vulnerability Testing"
    author: Jason Bau, Elie Bursztein, Divij Gupta, John Mitchell
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authors:
  - Jason Bau
  - Elie Bursztein
  - Divij Gupta
  - John Mitchell
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original_url: "https://web.stanford.edu/~jcm/papers/pci_oakland10.pdf"
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# State of the Art: Automated Black-Box Web Application Vulnerability Testing

**State of the Art: Automated Black-Box Web Application Vulnerability Testing** - Jason Bau, Elie Bursztein, Divij Gupta, John Mitchell, Publisher not stated.

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- Original: <https://web.stanford.edu/~jcm/papers/pci_oakland10.pdf>
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# State of the Art: Automated Black-Box Web Application Vulnerability Testing

State of the Art: Automated Black-Box Web Application Vulnerability Testing


                                       Jason Bau, Elie Bursztein, Divij Gupta, John Mitchell
                                                        Stanford University
                                                           Stanford, CA
                                   {jbau, divijg}@stanford.edu, {elie, mitchell}@cs.stanford.edu


   Abstract—Black-box web application vulnerability scanners           perform malevolent actions that range from gaining unau-
are automated tools that probe web applications for security           thorized account access [1] to obtaining sensitive data such
vulnerabilities. In order to assess the current state of the art, we   as credit card numbers [2]. In the extreme case, these vulner-
obtained access to eight leading tools and carried out a study
of: (i) the class of vulnerabilities tested by these scanners, (ii)    abilities may reveal the identities of intelligence personnel
their effectiveness against target vulnerabilities, and (iii) the      [3]. Because of these risks, web application vulnerability
relevance of the target vulnerabilities to vulnerabilities found       remediation has been integrated into the compliance pro-
in the wild. To conduct our study we used a custom web                 cess of major commercial and governmental standards, e.g.
application vulnerable to known and projected vulnerabilities,         the Payment Card Industry Data Security Standard (PCI
and previous versions of widely used web applications con-
taining known vulnerabilities. Our results show the promise            DSS), Health Insurance Portability and Accountability Act
and effectiveness of automated tools, as a group, and also             (HIPAA), and the Sarbanes-Oxley Act. To meet these man-
some limitations. In particular, “stored” forms of Cross Site          dates, web application scanners that detect vulnerabilities,
Scripting (XSS) and SQL Injection (SQLI) vulnerabilities are           offer remediation advice, and generate compliance reports.
not currently found by many tools. Because our goal is to              Over the last few years, the web vulnerability scanner market
assess the potential of future research, not to evaluate specific
vendors, we do not report comparative data or make any                 as become a very active commercial space, with, for exam-
recommendations about purchase of specific tools.                      ple, more than 50 products approved for PCI compliance
                                                                       [4].
  Keywords-Web Application Security; Black Box Testing;
Vulnerability Detection; Security Standards Compliance;                   This paper reports a study of current automated black-
                                                                       box web application vulnerability scanners, with the aim of
                       I. I NTRODUCTION                                providing the background needed to evaluate and identify
                                                                       the potential value of future research in this area. To the
   Black-box web application vulnerability scanners are au-            best of our knowledge this paper is the most comprehensive
tomated tools that probe web applications for security vul-            research on any group of web scanners to date. Because we
nerabilities, without access to source code used to build the          were unable to find competitive open-source tools in this
applications. While there are intrinsic limitations of black-          area (see Section VII), we contacted the vendors of eight
box tools, in comparison with code walkthrough, automated              well-known commercial vulnerabilities scanners and tested
source code analysis tools, and procedures carried out by              their scanners against a common set of sample applications.
red teams, automated black-box tools also have advantages.             The eight scanners are listed in Table I. Our study aims to
Black-box scanners mimic external attacks from hackers,                answer these three questions:
provide cost-effective methods for detecting a range of im-
                                                                         1) What vulnerabilities are tested by the scanners?
portant vulnerabilities, and may configure and test defenses
                                                                         2) How representative are the scanner tests of vulnera-
such as web application firewalls. Since the usefulness of
                                                                            bility populations in the wild?
black-box web scanners is directly related to their ability
                                                                         3) How effective are the scanners?
to detect vulnerabilities of interest to web developers, we
undertook a study to determine the effectiveness of leading               Because our goal is to assess the potential impact of
tools. Our goal in this paper is to report test results and            future research, we report aggregate data about all scanners,
identify the strengths of current tools, their limitations, and        and some data indicating the performance of the best-
strategic directions for future research on web application            performing scanner on each of several measures. Because
scanning methods. Because this is an anonymized confer-                this is not a commercial study or comparative evaluation of
ence submission, we note that the authors of this study are            individual scanners, we do not report comparative detection
university researchers.                                                data or provide recommendations of specific tools. No single
   Web application security vulnerabilities such as cross-site         scanner is consistently top-ranked across all vulnerability
scripting, SQL injection, and cross-site request forgeries are         categories.
acknowledged problems with thousands of vulnerabilities                   We now outline our study methodology and summarize
reported each year. These vulnerabilities allow attackers to           our most significant findings. We began by evaluating the
                                                                                                Table I
set of vulnerabilities tested by the scanners. Since most                         S TUDIED V ULNERABILITY S CANNERS
of the scanners provide visibility into the way that target
vulnerability categories are scanned, including details of          Company     Product            Version   Scanning Profiles Used
the distribution of their test vector sets by vulnerability         Acunetix    WVS                6.5       Default and Stored XSS
classification, we use this and other measures to compare the       Cenzic      HailStorm Pro      6.0       Best Practices, PCI
                                                                                                             Infrastructure, and Session
scanner target vulnerability distribution with the distribution     HP          WebInspect         8.0       All Checks
of in-the-wild web application vulnerabilities. We mine the         IBM         Rational AppScan   7.9       Complete
latter from incidence rate data as recorded by VUPEN                McAfee      McAfee SECURE      Web       Hack Simulation and DoS
security [5], an aggregator and validator of vulnerabilities        N-Stalker   QA Edition         7.0.0     Everything
reported by various databases such as the National Vul-             Qualys      QualysGuard PCI    Web       N/A
nerability Database (NVD) provided by NIST [6]. Using               Rapid7      NeXpose            4.8.0     PCI
database results, we also compare the incidence rates of web
application vulnerability as a group against incidence rates
for system vulnerabilities (e.g. buffer overflows) as group.              detected any of our constructed second-order SQLI
   In the first phase of our experiments, we evaluate scan-               vulnerabilities, and the stored XSS detection rate was
ner detection performance on established web applications,                only 15%. Other limitations are discussed further in
using previous versions of Drupal, phpBB, and Wordpress,                  this paper.
released around January 2006, all of which include well-              Our analysis suggests room for improvement in detecting
known vulnerabilities. In the second phase of our experi-          vulnerabilities inserted in our testbed, and we propose po-
ments, we construct a custom testbed application containing        tential areas of research in Section VIII. However, we have
an extensive set of contemporary vulnerabilities in pro-           made no attempt to measure the financial value of these tools
portion with the vulnerability population in the wild. Our         to potential users. Scanners performing as shown may have
testbed checks all of the vulnerabilities in the NIST Web          significant value to customers, when used systematically as
Application Scanner Functional Specification [7] and tests         part of an overall security program. In addition, we did not
37 of the 41 scanner vulnerability detection capabililities        quantify the relative importance of detecting specific vulner-
in the Web Application Security Consortium [8] evaluation          abilities. In principle, a scanner with a lower detection rate
guide for web application scanners. (See Section VII).             may be more useful if the smaller number of vulnerabilities
Our testbed application also measures scanner ability to           it detects are individually more important to customers.
understand and crawl links written in various encodings and           Section II of this paper discusses the black box scanners
content technologies.                                              and their vulnerability test vectors. Section III establishes
   We use our custom application to measure elapsed scan-          the population of reported web vulnerabilities. Section IV
ning time and scanner-generated network traffic, and most          presents scanner results on Wordress, phpBB, and Drupal
importantly, we tested the scanners for vulnerability detec-       versions released around January 2006. Section V discusses
tion and false positive performance.                               testbed results by vulnerability category for the aggregated
   Our most significant findings include:                          scanner set and also false positives. Section VI contains
   1) The vulnerabilities for which the scanners test most         some remarks by scanner, on individual scanner performance
       extensively are, in order, Information Disclosure,          as well as user experience. Section VII discusses related
       Cross Site Scripting (XSS), SQL Injection, and other        work and section VIII concludes by highlighting research
       forms of Cross Channel Scripting (XCS). This testing        opportunities resultant from this work.
       distribution is roughly consistent with the vulnerability
       population in the wild.                                                      II. B LACK B OX S CANNERS
   2) Although many scanners are effective at following               We begin by describing the general usage scenario and
       links whose targets are textually present in served         software architecture of the black-box web vulnerability
       pages, most are not effective at following links through    scanners. We then discuss the vulnerability categories which
       active content technologies such as Java applets, Sil-      they aim to detect, including test vector statistics where
       verLight, and Flash.                                        available. Table I lists the eight scanners incorporated in
   3) The scanners as a group are effective at detecting           our study, which include products from several of the
       well-known vulnerabilities. They performed capably          most-established security companies in the industry. All the
       at detecting vulnerabilities already reported to VuPen      scanners in the study are approved for PCI Compliance
       from historical application versions. Also, the scanners    testing [4]. The prices of the scanners in our study range
       detected basic “reflected” cross-site scripting well,       from hundreds to tens-of-thousands of dollars. Given such
       with an average detection rate of over 60%.                 a wide price range and also variations in usability, potential
   4) The scanner performed particularly poorly at detect-         customers of the scanners would likely not make a purchase
       ing “stored” vulnerabilities. For example, no scanner       decision on detection performance alone.
                                  Test vectors


    Info leaks                                                                                 Table II
                                                                      C ONSENSUS V ULNERABILITY C LASSIFICATION ACROSS S CANNERS
 Configuration
                                                                           Classification               Example Vulnerability
        CSRF                                                               Cross-Site Scripting (XSS)   Cross-Site Scripting
                                                                           SQL Injection (SQLI)         SQL Injection
      Session                                                                                           Arbitrary File Upload
                                                                                                        Remote File Inclusion
                                                                           Cross Channel Scripting
         XCS                                                                                            OS Command Injection
                                                                                                        Code Injection
         SQLI                                                                                           Session Fixation
                                                                           Session Management           Session Prediction
         XSS
                                                                                                        Authentication Bypass
                                                                           Cross-Site Request Forgery   Cross Site Request Forgery
                 0     10        20         30       40         50
                                                                                                        SSL Misconfiguration
                                                                           SSL/Server Configuration
                                                                                                        Insecure HTTP Methods
                                                                                                        Insecure Temp File
           Figure 1.   Scanner Test Vector Percentage Distribution
                                                                                                        Path Traversal
                                                                           Information Leakage
                                                                                                        Source Code Disclosure
                                                                                                        Error Message Disclosure
A. Usage Scenario

   To begin a scanning session using a typical scanner, the          C. Vulnerability Categories Targeted by Scanners
user must enter the entry URL of the web application as
                                                                        As each scanner in our study is qualified for PCI com-
well as provide a single set of user login credentials for
                                                                     pliance, they are mandated to test for each of the Open
this application. The user then must specify options for the
                                                                     Web Application Security Project (OWASP) Top Ten 2007
scanner’s page crawler, in order to maximize page scanning
                                                                     [9] vulnerability categories. We also examine the scanning
coverage. Most scanners tested allow a “crawl-only” mode,
                                                                     profile customization features of each scanner for further
so that the user can verify that the provided login and the
                                                                     insight into their target vulnerability categories. All scanners
crawler options are working as expected. After setting the
                                                                     except Rapid7 and Qualys allow views of the scanning
crawler, the user then specifies the the scanning profile, or
                                                                     profile by target vulnerability category, which are often
test vector set, to be used in the vulnerability detection
                                                                     direct from the OWASP Top Ten 2007 and 2010rc1, Web
run, before launching the scan. All scanners can proceed
                                                                     Application Security Consortium (WASC) Threat Classifica-
automatically with the scan after profile selection, and most
                                                                     tion version 1 [10], or the Common Weakness Enumeration
include interactive modes where the user may direct the
                                                                     (CWE) top 25 [11]. In fact, each of the six allow very
scanner to scan each page. In our testbed experiments,
                                                                     fine-grained test customization, resulting in a set of over
we always set the scanner to run, in automated mode,
                                                                     100 different targeted vulnerability categories, too numerous
the most comprehensive set of tests available, to maximize
                                                                     to list here. However, when related vulnerability categories
vulnerability detection capability.
                                                                     were combined into more general classifications, we were
                                                                     able to find a set of consensus classifications for which all
B. Software Architecture Descriptions                                tools test. Table II presents this list of consensus classifi-
                                                                     cations, along with some example vulnerabilities from each
   We ran two of the tested scanners, McAfee and Qualys, as          classification. We have kept Cross-Site Scripting and SQL
remote services whereby the user configures the scanner via          Injection as their own vulnerability classifications due to
a web-interface before launching the scan from a vendor-             their preponderant rate of occurrence (supported by “in the
run server farm. The other six scanners were tested as               wild” data in the next section) and their targeting by all
software packages running on a local computer, although              scanners. The Cross Channel Scripting classification [12]
the NeXpose scanner runs as a network service accessed by            includes all vulnerabilities, including those listed in the
browser via an IP port (thus naturally supporting multiple           table, allowing the user to inject code “across a channel”
scanner instances run by one interface). All scanners, as            onto the web server that executes on the server or a client
would be expected of black box web-application testers,              browser, aside from XSS and SQLI.
generate http requests as test vectors and analyze the http
response sent by the web server for vulnerabilities. All local       D. Test Vector Statistics
scanner engines seem to run in a single process, except for             We were able to obtain detailed enough test profile infor-
the Cenzic scanner, which runs a separate browser process            mation for four scanners (McAfee, IBM, HP, and Acunetix)
that appears to actually render the http response in order to        to evaluate how many test vectors target each vulnerabilities
find potential vulnerabilities therein.                              classification, a rough measure of how much “attention”
                                                                                                 Table III
scanner vendors devote to each classification. Figure 1 plots      P REVIOUSLY-R EPORTED VS S CANNER -F OUND V ULNERABILITIES F OR
the percentage of vectors targeting each classification aggre-                    D RUPAL , PHP BB2, AND W ORDPRESS
gated over the four scanners. The results show that scanners
                                                                                    Drupal           phpBB2             Wordpress
devote most testing to information leakage vulnerabilities,
                                                                    Category         4.7.0            2.0.19           1.5strayhorn
followed by XSS and SQLI vulnerabilities.                                       Known     Found   Known    Found     Known Found
                                                                    XSS         6         2       5        2         13         7
        III. V ULNERABILITY P OPULATION FROM                        SQLI        2         1       1        1         8          4
                 V U P EN -V ERIFIED NVD                            XCS         4         0       1        0         8          3
   In order to evaluate how well the vulnerability categories       Session     5         4       4        4         6          5
                                                                    CSRF        2         0       1        0         1          1
tested by the scanners represent the web application vulner-
                                                                    Info Leak   4         3       1        1         6          4
ability population “in the wild”, we took all of the web vul-
nerability categories forming the consensus classifications
from Table II and performed queries against the VUPEN
                                                                   by the website operator and thus cannot be detected by web
Security Vulnerability Notification Service database for the
                                                                   application scanning. In effect, the number of SSL/Server
years 2005 through 2009. We chose this particular database
                                                                   configuration vulnerabilities that web application scanners
as our reference as it aggregates vulnerabilities, verifies them
                                                                   may reasonably aim to detect does not appear to increase
through the generation of successful attack vectors, and
                                                                   with the increased SSL vulnerability incidence rate.
reports them to sources such as the Common Vulnerabilities
and Exposures (CVE) [13] feed of the National Vulnerability           Finally, Figures 2 and 3 suggest that 2006 was a particu-
Database.                                                          larly high-incident year for web application vulnerabilities,
   We collected from the VUPEN database the relative               with incidents actually decreasing in subsequent years. (This
incidence rate trends of the web application vulnerability         trend is also confirmed by searches in the CVE database.)
classes, which are plotted in Figure 2. Figure 3 plots             While it is impossible to be certain, evidence gathered during
incidences of web application vulnerabilities against in-          the course of this study, including the effectiveness of the
cidences of system vulnerabilities, e.g. Buffer Overflow,          scanners at detecting basic XSS and SQLI vulnerabilities,
Integer Overflow, Format String, Memory Corruption, and            suggests that the decrease may possibly be attributable to
Race Conditions, again collected by us using data from             headway made by the security community against these
VUPEN.                                                             vulnerabilities. Improved security, however, has been an-
   Figure 2 demonstrates that Cross-Site Scripting, SQL            swered in turn by efforts to uncover more novel forms of
Injection, and other forms of Cross-Channel Scripting have         the vulnerabilities.
consistently counted as three of the top four reported web
                                                                          IV. S CANNER R ESULTS ON C OMMON W EB
application vulnerability classes, with Information Leak be-
                                                                                      A PPLICATIONS
ing the other top vulnerability. These are also the top four
vulnerability classes by scanner test vector count. Within            Having confirmed that the testing vector distribution of
these four, scanner test vectors for Information Leak amount       black-box web vulnerability scanners as a group roughly
to twice that of any other vulnerability class, but the Infor-     correlates with the vulnerability population trends in the
mation Leak incidence rates in the wild are generally lower        wild, we now examine whether the scanners are actually
than that of XSS, SQLI, and XCS. We speculate that perhaps         successful at finding existent vulnerabilities. We ran all scan-
test vectors for detecting information leakage, which may          ners on three popular web applications, Drupal, phpBB2, and
be as simple as checking for accessible common default             Wordpress, all with known vulnerabilities. We chose to scan
pathnames, are easier to create than other test types. Overall,    application versions released around January 2006, as this
however, it does appear that the testing emphasis for black-       was prior to the peak in vulnerability reports in 2006. While
box scanners as a group is reasonably proportional to the          these are field applications with some inherent uncertainty as
verified vulnerability population in the wild.                     to their exact vulnerability content, the early release dates
   We believe that the increase in SSL vulnerabilities shown       mean these application versions are the most field-tested,
in figure 2 does not indicate a need for increased black-          with most vulnerabilities likely to have been recorded by
box scanning. A large number of SSL vulnerabilities were           VUPEN via the NVD.
reported in 2009, causing the upward trend in SSL in-                 Table III lists the specific application versions tested as
cidences. However, these are actually certificate spoofing         well as the number of known vulnerabilities, including those
vulnerabilities that allow a certificate issued for one domain     reported by the VUPEN database for each of these versions.
name, usually containing a null-character, to become valid         For all applications, we installed only the default modules
for another domain name [14], [15]. As this vulnerability is       and included no add-ons.
caused by mistakes made by the certificate authority and the          Table III also shows the number of vulnerabilities found
client application (usually browser), it cannot be prevented       by any scanners in the group, out of the set of known
                                                                                     Evolution of the web vulnerabilities over the years by types
                                             1000
                                                                                                                                                       XSS
                                                 900                                                                                                   SQLi
                                                                                                                                                       XCS
                                                 800                                                                                                   Session
                                                                                                                                                       CSRF
                                                 700                                                                                                   SSL
                                                                                                                                                       Infomation Leak
                   Number of vulnerability
                                                 600

                                                 500

                                                 400

                                                 300

                                                 200

                                                 100

                                                   0
                                                         2005                      2006                         2007                           2008           2009


                                                          Figure 2.       Comparison of Web Application Vulnerability Classes in VUPEN Database
                                                                                    Evolution of the number of vulnerabilties by years
                                                 3000
                                                                Web                       2793
                                                                System
                     Number of vulnerabilities




                                                                                          2000                   1951
                                                 2000


                                                                                                                                                         1647

                                                                                                               1528                       1531
                                                                                                                                                         1275

                                                                  1186
                                                                1095
                                                 1000
                                                                                                                                          996
                                                                   2005                   2006                  2007                      2008        2009


                                                       Figure 3.    Web Application Vulnerabilities versus System Vulnerabilities in VUPEN Database



vulnerabilities. As the table shows, the scanner in total did                                                      significantly smaller uncertainty in vulnerability content than
a generally good job of detecting these previously known                                                           in the case of field-deployed applications. (The scanners as a
vulnerabilities. They did particularly well in the Information                                                     group did not uncover any unintended vulnerabilities in our
Disclosure and Session Management classifications, leading                                                         web application.) We plan to release this testbed publically.
to the hypothesis that effective test vectors are easier to add                                                       For each vulnerability classification, we incorporated both
for these categories than others. The scanners also did a                                                          “textbook” instances and also forward-looking instances,
reasonable job of detecting XSS and SQLI vulnerabilities,                                                          such as XSS with non-standard tags, for each vulnerability
with about 50% detection rate for both. The low detection                                                          classification. However, we kept the vulnerability content
rate in the CSRF classification may possibly be explained                                                          of our testbed fairly proportional with the vulnerability
by the small number of CSRF test vectors. Anecdotally,                                                             population in the wild.
one scanner vendor confirmed that they do not report CSRF                                                             Our testbed has around 50 unique URLs and around
vulnerabilities due to the difficulty of determining which                                                         3000 lines of code, installed on a Linux 2.6.18-128.1.6.el5
forms in the application require protection from CSRF.                                                             server running Apache 2.2.3, MySQL 5.0.45, and PHP 5.1.6.
                                                                                                                   PhpMyAdmin was also running on our server alongside
      V. S CANNER R ESULTS ON C USTOM T ESTBED                                                                     the testbed application, solely for administrative purposes;
   In addition to testing scanner detection performance on                                                         we thus ignored any scanner results having to do with
established web applications, we also evaluated the scanners                                                       phpMyAdmin.
in a controlled environment. We developed our own custom                                                              The remainder of this section is devoted to scanner testbed
testbed application containing hand-inserted vulnerabilities,                                                      data. We begin by presenting the performance footprint of
each of which have a proven attack pattern. We verified each                                                       each scanner on our testbed. Following this, we report page
of the vulnerabilities present in this environment, allowing us                                                    coverage results, designed to test scanner understanding of
                                                                                                          Traffic generated
                                     Execution time
                                                                          Rapid7         186                          649
     Rapid7                  118

                                                                          Qualys    48      145
     Qualys                                                   473

   N-Stalker                             168                            N-Stalker     122                                   877


    McAfee                         138                                   McAfee 25 53


        IBM        66                                                        IBM    71      125

         HP             87                                                    HP 35          206

     Cenzic                  109                                          Cenzic    76      116
                                                                                                                                             Data sent
    Acunetix                                   241
                                                                         Acunetix     123          146                                       Data received


           0m 50m 100m150m200m250m300m350m400m450m500m                          0 MB     100 MB 200 MB 300 MB 400 MB 500 MB 600 MB 700 MB 800 MB 900 MB

               (a) Scanner Execution Time in Minutes                                              (b) Scanner Bytes Sent and Received
                                                       Figure 4.    Scanner Footprint



various content technologies. We then present vulnerability              are self explanatory. Figure 5 shows the experimental results,
detection results, first an overview and subsequently by                 where the measure is percentage of successful links crawled
vulnerability classification, giving a brief overview of our             over total existent links by technology category.
testbed design for each classification. Finally, we discuss                 Figure 5 shows that the scanners as a group have fairly
false positives, including experimentally designed “traps” for           low comprehension of active technologies such as Java
false positives as well as scanner results.                              applets, SilverLight, and, surprisingly given its widespread
                                                                         use, Flash. We speculate that some scanners only perform
A. Scanner Time and Network Footprint                                    textual analysis of http responses in order to collect URLs,
   Figures 4a and 4b respectively plot the time required to              thus allowing them to perform decently on script-based
scan the testbed application and the number of network bytes             links, which are represented in text, but not allowing them
sent/received by each scanner, as measured on the web server             to follow links embedded in compiled objects such as Java
by tcpdump. Scanning time ranged from 66 to 473 minutes,                 applets and Flash movies. This would also explain the better
while network traffic ranged from 80 MB to nearly 1 GB.                  coverage of SilverLight over Flash and Java, as SilverLight
   Perhaps surprisingly, the scanning time and network traf-             is delivered in a text-based markup language. We also
fic statistics seem to be relatively independent of each                 see that the scanners could improve their understanding of
other, as exemplified by the Rapid7, Qualys, N-Stalker,                  various link encodings.
and McAfee results. It is interesting that the two remote
services, Qualys and McAfee, generated comparatively low                 C. Vulnerability Detection Results
amounts of network traffic. Finally, we wish to note that                   1) Overall Results: Figure 6 presents by vulnerability
the footprint statistics are not indicative of vulnerability             classification the vulnerability detection rate averaged over
detection performance.                                                   all scanners. The detection rate is simply calculated as the
                                                                         number of vulnerabilities found over the (known) number of
B. Coverage Results                                                      total vulnerabilities. Results for each vulnerability classifi-
   To experimentally evaluate site coverage, we wrote hy-                cations, including an added malware detection classification,
perlinks using the technology in each category shown in                  are explained in detail in individual sub-sections to follow.
figure 5 and embedded each landing page with tracker code                Each vulnerability classification sub-section describes the
that measured whether the link was followed. For Java,                   testbed for the category, plots the average detection rate over
SilverLight, and Flash, the linked applet or movie is a                  all scanners, and also plots anonymous individual scanner
simple, bare shell containing only the hyperlink. We then                results for the category sorted from best- to worst-performing
link to the technology page containing the link from the                 for that category.
application home page, which is written in regular php.                     The results show that the scanners as a group are fairly
   The link encoding category encompasses links written                  effective at detecting basic “reflected” cross-site scripting
in hexadecimal, decimal, octal, and html encodings, with                 (XSS type 1), with a detection rate of over 60%. Also,
the landing page file named in regular ASCII. The “POST                  although not shown, basic forms of first-order SQL Injection
link” test involves a link that only shows up when certain               were detected by a majority of scanners. Unfortunately,
selections are made on a POST form. The other technologies               the overall results for the first-order SQL vulnerability
                                                                       Scanner coverage efficiency by type of link
                    110%
                                                                                                            100           100                                100
                    100%

                       90%                                                                                                                                              87.5

                       80%    79.16
                                                                                                                                                                                                   75
                       70%
                                                                                                                                                                                      62.5
                       60%
                                                                                                                                     53.12
                   %


                                               50                                                                                                 50
                       50%

                       40%                                  37.5

                       30%

                       20%
                                                                             12.5            12.5
                       10%

                       0%
                                Ja              AJ              Sil                Fla           Ja              PH          Me         Lin        Dy         Po            Ifra       VB              PO
                                     va           AX                  ve               sh             va              Pr         ta-        ke         na          p-u           me      Sc              ST
                                        scri                             r   Lig                           Ap           ed          ref        nc         mi           p                     rip            l
                                               pt                                  ht                           ple        ire         res        od         cj                                    t            ink
                                                    ev                                                              ts         cts         ht        ing        a va
                                                      en                                                                                     ag                      sc
                                                           ts                                                                                                          rip
                                                                                                                                                                           t

                 Figure 5.   Successful Link Traversals over Total Links by Technology Category, Averaged Over All Scanners.
                                                                                                      Scanners Overall detection rate
                              Malware 0
                              Info leak                                                                                                 31.2
                                Config                                                                                                   32.5
                               Session                                                                                         26.5
                         SQL 2nd order 0
                          SQL 1st order                                                                               21.4
                                 CSRF                                                                 15
                                   XCS                                                                             20.4
                          XSS advance                                                        11.25
                            XSS type 2                                                           15
                            XSS type 1                                                                                                                                                         62.5
                                        0%                                              10                       20                 30                 40                 50                  60
                                                                                             %                        %                  %                  %                  %                 %

                                            Figure 6.                 Average Scanner Vulnerability Detection Rate By Category



classification were dragged down by poor scanner detection                                                                  XSS, using non-standard tags and keywords, such <style>
of more complex forms of first-order SQL injection that use                                                                 and prompt() [16], or using alternative scripting tech-
different keywords. Aside from the XSS type 1 classification,                                                               nologies such as Flash. For XSS advanced tests using novel
there were no other vulnerability classifications where the                                                                 keywords, we filtered out any user inputs that did not contain
scanners as a group detected more than 32.5% of the                                                                         the appropriate keywords.
vulnerabilities. In some cases, scanners were unable to detect                                                                 As previously mentioned, Figure 7 shows that the scanners
testbed vulnerabilities which were an exact match for a cate-                                                               performed decently well on XSS type 1, with all scanners
gory listed in the scanning profile. We also note how poorly                                                                detecting at least 50% of the vulnerabilities. For the other
the scanners performed at detecting “stored” vulnerabilities,                                                               categories, however, the scanners performed poorly as a
i.e. XSS type 2 and second-order SQL injection, and how                                                                     group, with only the leading performer detecting more than
no scanner was able to detect the presence of malware. We                                                                   20% of vulnerabilities, and numerous scanners failing to
will discuss our thoughts on how to improve detection of                                                                    detect any vulnerabilities.
these under-performing categories in Section VIII.
                                                                                                                               3) SQL Injection: We also divided SQL Injection vulner-
   2) Cross-Site Scripting: Due to the preponderance of                                                                     abilities into two sub-classes, first-order and second-order,
Cross-Site Scripting vulnerabilities in the wild, we divided                                                                for the same reason as dividing the XSS classification. First-
Cross-Site Scripting into three sub-classes: XSS type 1, XSS                                                                order SQL Injection vulnerabilities results in immediate
type 2, and XSS advanced. XSS type 1 consists of textbook                                                                   SQL command execution upon user input submission, while
examples of reflected XSS, performed via the <script>                                                                       second-order SQL Injection requires unsanitized user input
tag. XSS type 2 consists of stored XSS vulnerabilities,                                                                     to be loaded from the database. The first-order SQL vul-
where un-sanitized user input is written to the database and                                                                nerability classification also includes both textbook vulnera-
later performs scripting when read from the database. XSS                                                                   bilities as well as vulnerabilities dependent on non-standard
advanced encompasses novel forms of reflected and stored                                                                    keywords such as LIKE and UNION, where user inputs not
                                                                       Scanner Detection Rate for X
                                                    11.25                                                                     8th
                                                                                           50                                 7th
                                                            20
                                                            20                                                                6th
                               XSS adv 0                                                                                      5th
                                           0                                                                                  4th
                                           0
                                                                                                                              3rd
                                           0
                                           0                                                                                  2nd
                                                       15                                                                     1st
                                                                                40                                            Average
                                                            20
                                                            20
                             XSS type 2                     20
                                                            20
                                           0
                                           0
                                           0
                                                                                                        62.5
                                                                                                                                 100
                                                                                                                                 100
                                                                                           50
                             XSS type 1                                                    50
                                                                                           50
                                                                                           50
                                                                                           50
                                                                                           50
                                      0%         10%    20%        30%      40%       50%         60%      70%    80%   90%    100%


                                   Figure 7.       XSS Detection Results Sorted By Scanner Rank in Category
                                                                 Scanner Detection Rate for SQL injections
                                           0                                                                                  8th
                                           0                                                                                  7th
                                                                                                                              6th
                                           0
                                                                                                                              5th
                                           0
                                                                                                                              4th
                               SQL 2nd 0                                                                                      3rd
                                           0                                                                                  2nd
                                           0                                                                                  1st
                                                                                                                              Average
                                           0
                                           0

                                                                                           21.4
                                                                                                                                 42.8
                                                                                                           28.5
                                                                                                           28.5
                               SQL 1st                                                                     28.5
                                                                         14.2
                                                                         14.2
                                                                         14.2
                                           0
                                      0%                    10%                      20%                   30%           40%


                               Figure 8.       SQL Injection Detection Results Sorted by Scanner Rank in Category



containing the appropriate keyword are again filtered out.                             Redirects, Cross-Frame Scripting, Server Side Includes,
Also, in all cases, malformed SQL queries in our testbed                               Path Traversal, Header Injection (HTTP Response Splitting),
result in a displayed SQL error message, so scanners do not                            Flash Parameter Injection, and SMTP Injection.
have to rely on blind SQL Injection detection.                                            As Figure 9 demonstrates, the scanners as a group per-
   Figure 8 shows that 7 of 8 scanners were able to detect                             formed fairly poorly on this class of vulnerabilities. Only
the basic first-order SQL injection vulnerability (accounting                          Server-Side Includes and Path Traversal were detected by a
for the 14.2%), but only one scanner was able to exceed                                majority of scanners.
40% rate of detection for all first-order SQL injection                                   5) Session Management: The Session vulnerability clas-
vulnerabilities. Similar to XSS results, second-order SQLI                             sification include session management flaws as well as
vulnerability detection is significantly worse than first-order,                       authentication and cookie flaws. The testbed authentica-
with no scanner able to detect even one such vulnerability.                            tion vulnerabilities include credentials being sent over un-
   4) Cross-Channel Scripting: As described in a previous                              encrypted HTTP, auto-complete enabled in the password
section, the Cross Channel Scripting classification includes                           field, submitting sensitive information over GET requests,
all vulnerabilities allowing the attacker to inject code onto                          weak password and password recovery questions, and weak
the web server that manipulates the server or a client                                 registration CAPTCHAs. The session management and
browser. In our testbed, this classification included vulner-                          cookie vulnerabilities include insecure session cookies, non-
abilities in XPath injection, Malicious File Upload, Open                              HttpOnly cookies, too broad cookie path restrictions, pre-
                                                      Scanner Detection Rate for XCS vulnerabilities
                                                                  20.4

                                                                                                                          54.54

                                                                                            36.36                     8th
                                                                           27.27                                      7th
                                                                                                                      6th
                            XCS                                18.18                                                  5th
                                                               18.18                                                  4th
                                                                                                                      3rd
                                               9.09
                                                                                                                      2nd
                                   0                                                                                  1st
                                                                                                                      Average
                                   0
                                  0%          10%              20%           30%                 40%            50%


                          Figure 9.    Cross-Channel Scripting Detection Results Sorted by Scanner Rank in Category
                                                        Scanner Detection Rate for session vulnerabilities

                                                                                          26.5


                                                                                                                            43.75


                                                                                                               37.5


                                                                                                       31.25


                                  Session                                            25

                                                                                                                      8th
                                                                                     25                               7th
                                                                                                                      6th
                                                                                                                      5th
                                                                          18.7
                                                                                                                      4th
                                                                                                                      3rd
                                                                          18.7                                        2nd
                                                                                                                      1st
                                                                12.5
                                                                                                                      Average

                                        0%               10%              20%                    30%             40%


                     Figure 10.   Session Management Vulnerability Detection Results Sorted by Scanner Rank in Category



dictable session and authentication id values, session fixa-                     of the vulnerabilities in this classification, with one vendor
tion, ineffective logout, mixed content pages, and caching                       confirming that they did not report CSRF vulnerabilities at
of sensitive content.                                                            the time of testing.
   As a group, the scanners performed better at detecting this                      7) Information Disclosure: Our testbed application leaks
vulnerability class than the SQLI, XSS, and XCS classes.                         sensitive information regarding SQL database names via the
Figure 10 shows that scanner performance is fairly evenly                        die() function and existent user names via AJAX requests.
distributed between the best performer at 43.7% detection                        Backup source code files are also left accessible, and path
and the worst at 12.5% detection.                                                disclosure vulnerabilities are also present.
   6) Cross-Site Request Forgery: Nearly all forms on our                           Figure 12 shows that this was one of two vulnerability
testbed application do not use any sort of randomized                            categories where the scanners as a group performed the
authentication token, making them vulnerable to Cross-Site                       best. A majority of scanners detected all of the backup file
Request Forgery. However, we only considered as requiring                        disclosures, as well as the path disclosure vulnerabilities.
CSRF protection the forms which are only available after                            8) Server and Cryptographic Configuration: While
login. Our testbed contains post-login forms without any                         server and cryptography vulnerabilities do not technically
authorization token and also post-login form which utilize                       occur at the application layer, they affect web application
tokens with very few bits of entropy. In addition to the CSRF                    security all the same and should be detected by the vulnera-
vulnerabilities just mentioned, our testbed also included                        bility scanners. Our server configuration contained improper
session tokens that do not reset after form submission, GET-                     PHP setting in the ‘open basedir’ and ‘allow url fopen’
method forms vulnerable to CSRF, and CSRF-like JSON                              variables and allowed the HTTP TRACE request. The SSL
hijacking vulnerabilities.                                                       of the server was also mis-configured, with a self-signed
   Results in Figure 11 show that two scanners fared rela-                       SSL certificate and weak cipher strength.
tively well at CSRF detection, each achieving 40% detection                         Figure 13 shows that this was the other of the two
rates. On the other extreme, four scanners detected none                         vulnerability categories where the scanners as a group
                                                   Scanner Detection Rate for CSRF vulnerabilities
                                                                 15

                                                                                                                          40

                                                                                                                          40

                                                                             20                                     8th
                                                                                                                    7th
                         CSRF                                                20
                                                                                                                    6th
                                0                                                                                   5th
                                                                                                                    4th
                                0                                                                                   3rd
                                                                                                                    2nd
                                0
                                                                                                                    1st
                                0
                                                                                                                    Average

                              0%                    10%                     20%                     30%               40%

                        Figure 11.     Cross-Site Request Forgery Detection Results Sorted by Scanner Rank in Category
                                                       Scanner Detection Rate for information leaks

                                                                                             31.2


                                                                                                                          50


                                                                                                                          50


                                                                                                                          50


                           Info leak                                              25

                                                                                                                8th
                                                                                  25                            7th
                                                                                                                6th
                                                                                  25                            5th
                                                                                                                4th
                                                                                                                3rd
                                                                                  25
                                                                                                                2nd
                                                                                                                1st
                                                                                  25                            Average

                                     0%             10%               20%              30%                40%         50%

                          Figure 12.      Information Disclosure Detection Results Sorted by Scanner Rank in Category



performed the best. Seven of eight scanners detected the                      section. However, as Figure 6 demonstrates, no scanner
TRACE request vulnerability. On the other hand, we were                       reported the presence of any malware on our testbed site.
surprised that less than half of the scanners detected the self-
signed SSL certificate, as this seems to be a simple check                    D. False Positive Results
to prevent significant impact on the user-experience of the                      We designed two potential “traps” for false positives in
site, especially with newer browsers.                                         our testbed. The first involves using javascript alert()
   9) Detection of Malware: Finally, we decided to add the                    as intended site behavior, to see if any scanner would
detection of malware as a category in the scanner testbed.                    wrongly classify this as a sign of a Cross-Site Scripting
With the proliferation of open-source code, it is uncertain                   vulnerability. The second involves inserting user input into
whether website operators are familiar with the entirety of                   the right-hand side of a Javascript string variable assignment
the codebase which operates their site. Malware detection                     within a <script> block but not doing anything else with
serves as a check that websites are not unwitting partners                    that variable. Any quotation symbols in the user input that
aiding malicious third-parties in exploiting their users. This                would create a genuine XSS vulnerability are html-encoded
feature is also useful as a defense-in-depth measure in the                   by the testbed, and all ‘;’ characters are filtered. This in
case that attackers have succeeded in injecting malicious                     effect creates a benign region within a <script> block
code onto the site. Thus, we inserted simple pieces of                        that reflects user input, which can trap scanners simply
malware on our testbed site, a javascript keystroke logger                    searching for user-manipulable text within script blocks.
at the login page and a malicious file in the user-content                    The “alert()” trap did not cause any false positives, but
                                                 Scanner Detection Rate for server configuration errors

                                                                                        32.5


                                                                                                                               60


                                                                                                                               60


                                                                                                                               60


                               Config                          20

                                                                                                                     8th
                                                               20                                                    7th
                                                                                                                     6th
                                                               20                                                    5th
                                                                                                                     4th
                                                                                                                     3rd
                                                               20
                                                                                                                     2nd
                                                                                                                     1st
                                        0                                                                            Average

                                    0%          10%          20%              30%               40%           50%         60%

             Figure 13.   Server and Cryptographic Configuration Vulnerability Detection Results Sorted by Scanner Rank in Category
                                                                                                          False positive by scanners

the benign region within a <script> block caused false                         8    0

positives in two scanners–one reporting the false positive in                  7    0

                                                                               6    0
a single URL and the other in 13 different URLs.
                                                                    Scanner




                                                                               5         2

                                                                               4         2

                                                                               3                         14
   Figure 14 plots the number of false positives reported by
                                                                               2                                19
each scanner in sorted order for this category. For reference,                 1                                                                         51
there are around 90 total confirmed vulnerabilities in our
testbed. It is noteworthy that several scanners reported no                        0              10            20             30       40          50

false positives, and that some of the scanners with low
false-positives also had among the highest vulnerability                                 Figure 14.    False Positive Count in Sorted Order By Scanner
detection rates. The two scanners with the highest number of
false positive, both with vulnerability detection rates among
                                                                                               VI. E XPERIMENTAL AND S CANNER U SAGE
the lowest, reported numerous accessible code backup files
                                                                                                           O BSERVATIONS
where none existed. The worst performing scanner for false
positives also reported false file inclusion, SQL Injection,                     We have thus far focused primarily on the detection per-
IP disclosure, path disclosure, and forms accepting POST                      formance of the scanners as a group of different vulnerability
parameters form GET requests. This scanner also clas-                         classifications. In this section, we will remark on some by-
sifies hidden form values as vulnerabilities, contradicting                   scanner characteristics, without making overall comparative
established practices for CSRF prevention using hidden                        rankings of one product versus another.
form authentication tokens. Among all other scanners, the                        We observed that no individual scanner was a top-
only other false positives of note are a CSRF vulnerability                   performer in every vulnerability classification. Often, scan-
reported despite the presence of an authentication token, and                 ners with a leading detection rate in one vulnerability
auto-complete being reported for a password field where it                    category lagged in other categories. For example, the leading
was actually turned-off.                                                      scanner in both the XSS and SQL Injection categories was
                                                                              among the bottom three in detecting Session Management
                                                                              vulnerabilities, while the leader for Session Vulnerabilities
   Finally, some scanners emit general warnings when they                     lagged in XSS and SQLI. This leads us to believe that
detect a potential vulnerability, such as a GET form method                   scanner vendors may benefit as a community from a cross-
or a form without hidden authentication fields, without actu-                 vendor-pollination of ideas.
ally pinpointing the URL of the offending forms. We counted                      Reiterating briefly from the false positive results, we did
these as detections in our data-collection methodology, but,                  find that scanners with high detection rates were able to
given the general nature of these warnings, could have just                   effectively control false positives, and that scanners with
as easily listed them as false positives.                                     low detection rates could produce many false positives.
Additionally, there were reticent scanners that reported few       but their self-reported detection rates are in general higher
total vulnerabilities, making both detection rate and false        than our rates, since manual white-box security audits, which
positive count low.                                                have higher reported detection rates, are also included in the
   The remote versus local distinction in scanner architecture     study.
makes for interesting choices for the scanner customer. In            In addition, NIST [7] and WASC [8] have published eval-
our experimental experience, remote scanners were conve-           uation criteria for web application scanners. We consulted
nient as they experienced no install and system compatibility      these public categorizations and scanner evaluation guides
issues, offered portable user-interface and report-storage, ran    to ensure the comprehensiveness of our testbed. Our testbed
with complete automation after the initial test configuration,     checks all of the recommendations in the NIST guide and
and did not consume internal network and system resources.         37 of the 41 first-and-second-level testing capability listed
On the other hand, commercial enterprises may be concerned         by WASC.
with privacy and information disclosure issues resulting from         Almost all academic research on tools for web applica-
conducting scans over a public network. In response to             tion security has been source code analysis, with a focus
customer preferences, some vendors, such as Cenzic and             on detecting XSS and SQLI via information flow, model-
Rapid7, offer scanners both as a remote service and a local        ing checking analysis, or a combination thereof. Work by
software package. In our experiments, we observed that the         Wassermann [20], Lam [21], Kieżun [22], Jovanovic [23],
architecture (local versus remote) of the scanners did not         and Huang [24] all fall into this category.
appear to be a factor in overall detection results.                   Kals et. al. [25] and McAllister et. al. [26] implemented
   We also wish to remark on the user experience of the            automated black box web vulnerability scanners, with the
scanners, specifically regarding test automation. Most tools       former targeting SQLI and XSS vulnerabilities and the latter
offer a choice between interactive and automated scanning          utilizing user interactions to generate more effective test
modes, and we anticipate that, given the expected run-time         cases targeting reflected and stored XSS. Maggi et. al. [27]
of the scanners, many users will select the automated mode.        discuss techniques to reduce false positive counts in auto-
On a particular tool, however, even the automated mode             mated intrusion detection, which is applicable to black-box
requires user-interaction to dismiss javascript alert()            scanning. Interesting open-source scanner projects include
boxes, ironically inserted by the tool’s XSS test vectors. This    W3AF [28] and Powerfuzzer [29], which we evaluated but
caused workflow disruption in our laboratory environment,          did not include in the study due to their lack of testing
so we expect that it would carry over when scanning larger,        for authentication and server vulnerabilities, and Nikto [30],
deployed applications.                                             which in counterpoint to W3AF and PowerFuzzer focuses
   Finally, we wish to note that while the vulnerability           on server vulnerabilities instead of user-input validation.
detection rates reported in this paper are generally less             In terms of testbeds for black-box web application vul-
than 50%, this fact by itself should not be considered an          nerability scanners, there are a number of “vulnerability
indictment against the usefulness of automated black-box           demonstration sites”, such as WebGoat by OWASP [31],
scanners. Black-box scanners may in fact prove to be very          Hacme Bank [32], and AltoroMutual [33], that offer vul-
useful components in security-auditing programs upon more          nerability education for website developers as well as sales-
detailed consideration of factors such as cost and time saved      demonstration for scanner product capabilities. Due to their
from manual review.                                                well-known status and/or intended purpose, we did not
                                                                   evaluate any of the scanners on these sites as we did not
                    VII. RELATED WORK
                                                                   view the site as independent testbeds. However, Suto [34]
   Much regulatory and industry effort has been devoted            has produced an interesting comparison of seven black-box
to vulnerability categorization. The Common Vulnerabilities        scanners by running the products against several of these
and Exposures database [13] (CVE) feed of the NVD,                 demonstration sites. Finally, Fonseca et. al. [35] evaluated
sponsored by the US Dept. of Homeland Security, associates         the XSS and SQLI detection performance of three anony-
each vulnerability in its database with a Common Weakness          mous commerical application via automated software fault-
Enumeration (CWE) category [11], which include but are not         injection methods.
limited to web application categories. Industry web applica-
tion security special interest groups OWASP [17] and WASC                              VIII. C ONCLUSION
[18] have published web vulnerability-specific classifications
in their Top Ten [9] and [10] projects respectively. WASC             We studied the vulnerabilities that current black-box scan-
has also published a report on web-vulnerability statistics        ners aim to detect and their effectiveness in detecting these
[19], with vulnerability and detection rate data sourced from      vulnerabilities. Our survey of web-application vulnerabilities
automated black-box scanner, manual black-box penetration          in the wild shows that Cross-Site Scripting, SQL Injection,
testing, and white-box security auditing vendors. The vul-         other forms of Cross-Channel Scripting, and Information
nerability statistics they report are supportive of our results,   Disclosure are the most prevalent classes of vulnerabilities.
Further, we found that black-box web application vulnera-         understanding of active content and scripting languages.
bility scanners do, in general, expend testing effort in rough
proportion to the vulnerability population in the wild. As                             ACKNOWLEDGMENT
shown by our experimental results on previous versions               The authors would like to thank Acunetix, Cenzic, IBM,
of popular applications and textbook cases of Cross-Site          McAfee, Qualys, and Rapid7 for their participation in this
Scripting and SQL Injection, black-box scanners are adept         study.
at detecting straightforward historical vulnerabilities.
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