Man-in-the-Middle Attack Against SSL 3.0/TLS 1.0
It’s the Browser Exploit Against SSL/TLS Tool, or BEAST:
Using the known text blocks, BEAST can then use information collected to decrypt the target’s AES-encrypted requests, including encrypted cookies, and then hijack the no-longer secure connection. That decryption happens slowly, however; BEAST currently needs sessions of at least a half-hour to break cookies using keys over 1,000 characters long.
The attack, according to Duong, is capable of intercepting sessions with PayPal and other services that still use TLS 1.0which would be most secure sites, since follow-on versions of TLS aren’t yet supported in most browsers or Web server implementations.
While Rizzo and Duong believe BEAST is the first attack against SSL 3.0 that decrypts HTTPS requests, the vulnerability that BEAST exploits is well-known; BT chief security technology officer Bruce Schneier and UC Berkeley’s David Wagner pointed out in a 1999 analysis of SSL 3.0 that “SSL will provide a lot of known plain-text to the eavesdropper, but there seems to be no better alternative.” And TLS’s vulnerability to man-in-the middle attacks was made public in 2009. The IETF’s TLS Working Group published a fix for the problem, but the fix is unsupported by SSL.
EDITED TO ADD: Good analysis.