Macromedia Flash Communication Server MX 1.0 and 1.5 does not sufficiently validate certain RTMP data, which allows attackers to cause a denial of service (instability or crash), as demonstrated using an alpha release build of Flash Player 8.5 (build 133).
http://www.securityfocus.com/bid/15437
http://www.macromedia.com/devnet/security/security_zone/mpsb05-09.html