FFmpeg 0.5 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via unknown vectors that trigger a stack-based buffer overflow.
https://roundup.ffmpeg.org/roundup/ffmpeg/issue1240
http://www.vupen.com/english/advisories/2010/0935
http://www.ubuntu.com/usn/USN-931-1
http://www.securityfocus.com/bid/36465
http://www.debian.org/security/2010/dsa-2000
http://secunia.com/advisories/39482