Whitepaper: 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 summarizing these problems, with interesting proof-of-concept attacks against Google's new CSRF 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 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.

--Mike Bailey

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