Adobe Flash Player Multimedia File Remote Buffer Overflow Vulnerability
"Application-Specific Attacks: Leveraging the ActionScript Virtual Machine", a paper by Mark Dowd of X-Force IBM ISS, describes in detail the techniques required to exploit this issue and serves as a proof of concept. Please see the references for more information.
An exploit and a proof of concept are available for members of Immunity's CANVAS Early Update Program:
Core Security Technologies has developed a working commercial exploit for its CORE IMPACT product. This exploit is not otherwise publicly available or known to be circulating in the wild.
Symantec has observed that this issue is being actively exploited in the wild.
UPDATE: Continued investigation reveals that this issue is fairly widespread. Malicious code is being injected into other third-party domains (approximately 20,000 web pages), most likely through SQL-injection attacks. The code then redirects users to sites hosting malicious Flash files exploiting this issue.