An attacker cannot directly exploit this vulnerability, and instead must rely upon user participation in order to accomplish an exploit. An attacker may attempt to embed malicious content on compromised websites that launch exploits against users who visit those sites. Attackers may also attempt to convince users to visit malicious sites by sending links within e-mail messages to users.
If an exploit is successful, the attacker could execute arbitrary code with the privileges of the user. Exploitation on systems that allow users to run programs with Administrator privileges could result in a complete compromise. However, the impact is likely to be less on systems that only allow users to run programs with limited privileges, as any executed code would run in a restricted security context.
The Cisco Applied Intelligence team has created an Applied Mitigation Bulletin to address vulnerabilities that Microsoft disclosed in the July 2009 security bulletin release. This Cisco bulletin, which assists administrators in identifying or mitigating these vulnerabilities using Cisco devices, is available at the following link: Cisco Applied Mitigation Bulletin: Microsoft Security Bulletin for July 2009
The update available from Microsoft corrects this vulnerability by properly checking the size of parameters within QuickTime content.