A buffer overflow vulnerability in Fortinet FortiOS 6.0.0 through 6.0.4, 5.6.0 through 5.6.7, 5.4 and earlier versions and FortiProxy 2.0.0, 1.2.8 and earlier versions under SSL VPN web portal allows a non-authenticated attacker to perform a Denial-of-service attack via special craft message payloads.