Enforces the flaw's applicability in real world attacks

Nov 16, 2009 11:33 GMT  ·  By

A security researcher has devised a practical Man-in-the-Middle (MITM) attack leveraging the recently disclosed SSL and TLS renegotiation flaw. The proof-of-concept attack shows that it is possible to steal login credentials from Twitter by exploiting the yet unpatched bug.

Two weeks ago, it was revealed that a serious security issue affecting the widely deployed SSL and TLS protocols was being patched in secret by several major technology vendors. The patching effort apparently began in September, but so far only OpenSSL is close to releasing a working fix.

The flaw, discovered by Marsh Ray, a researcher working for a two-factor tokenless authentication solution provider, is located in the session renegotiation procedure. By exploiting this flaw during a Man-in-the-Middle condition, an attacker can insert plain text, possibly rogue commands, into a secure session.

Some professionals have dismissed the seriousness of the problem for Web implementations, especially since it can't be used to extract information from a session's encrypted data. However, a Turkish researcher named Anil Kurmus disagrees and has recently presented a real world attack scenario based on the bug.

In his PoC attack, Kurmus successfully intercepts requests sent to the Twitter API and drops their content onto his own Twitter feed by exploiting this flaw. This attack is practical, because requests sent to the Twitter API always contain the username and password and a lot of people post on the micro-blogging platform through third-party applications.

"All in all, a man in the middle is able to steal the credentials of a user authenticating himself through HTTPS to a trusted website, and CSRF protections do not apply here," Kurmus, who is a grad student at the French Eurecom Institute, concludes. And while Twitter has moved swiftly to patch the hole, which made this attack possible on their end, the researcher's attack stands proof that if certain conditions are met, websites are vulnerable.

PhoneFactor, the company Marsh Ray works for, and which coordinated the vendor disclosure process, maintains a patching status page for this vulnerability. According to it, OpenSSL is close to making a patch generally available while Microsoft is still performing interoperability testing for its own fix.