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title: "Skeptikal.org: Cross-subdomain Cookie Attacks"
description: "Announces a Toorcon talk and paper on client-side trust in subdomains. Cookie scoping implements its security policy backwards, granting a subdomain more trust than its parent rather than less as the DNS hierarchy would suggest. Proofs of concept target Google's then-new CSRF protection and Expedia; both were fixed before publication."
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    title: "Skeptikal.org: Cross-subdomain Cookie Attacks"
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# Skeptikal.org: Cross-subdomain Cookie Attacks

**Skeptikal.org: Cross-subdomain Cookie Attacks** - Mike Bailey, skeptikal.org.

- Published: date not stated
- Original: <http://skeptikal.org/2009/11/cross-subdomain-cookie-attacks.html>
- Preserved from: http://skeptikal.org/2009/11/cross-subdomain-cookie-attacks.html (stored) on 2026-08-09
- Capture timestamp: 20091111042501
- Licence: unknown

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## Content

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Skeptikal.org: Cross-subdomain Cookie Attacks

###  Cross-subdomain Cookie Attacks

I did a talk at Toorcon last weekend on exploiting client-side applications' trust in subdomains. Primarily, it formalized and demonstrated a few attacks on cookies, which implement security policies backwards by placing more trust in a subdomain of a trusted domain, rather than less, as the hierachical nature of DNS would suggest.

Last night, I put together a [quick paper](http://skeptikal.org/repository/one_in_every_family.pdf) summarizing these problems, with interesting proof-of-concept attacks against Google's new [CSRF protection](http://www.theregister.co.uk/2009/10/02/google_web_attack_protection/) feature and Expedia.

I'm still looking into the ways that other client-side technologies (Flash, Java, etc) handle these issues, so expect a version 2.0 in the future. Also, I'm looking forward to some relevant [new tools](http://www.owasp.org/index.php/Synergy%21_A_world_where_the_tools_communicate) that will be released at AppSec DC next week.

Note: All the attacks outlined in this paper were responsibly disclosed, and the Google and Expedia ones, specifically, have been fixed for several weeks.