FortiOS 5.0.x before 5.0.12 and 5.2.x before 5.2.4 supports anonymous, export, RC4, and possibly other weak ciphers when using TLS to connect to FortiGuard servers, which allows man-in-the-middle attackers to spoof TLS content by modifying packets.
http://www.securitytracker.com/id/1033092