A Cross-site Scripting (XSS) vulnerability in Fortinet FortiOS 6.0.0 to 6.0.4, 5.6.0 to 5.6.7, 5.4.0 to 5.4.12, 5.2 and below and Fortinet FortiProxy 2.0.0, 1.2.8 and below under SSL VPN web portal allows attacker to execute unauthorized malicious script code via the error or message handling parameters.