FortiClient before 4.3.5.472 on Windows, before 4.0.3.134 on Mac OS X, and before 4.0 on Android; FortiClient Lite before 4.3.4.461 on Windows; FortiClient Lite 2.0 through 2.0.0223 on Android; and FortiClient SSL VPN before 4.0.2258 on Linux proceed with an SSL session after determining that the server's X.509 certificate is invalid, which allows man-in-the-middle attackers to obtain sensitive information by leveraging a password transmission that occurs before the user warning about the certificate problem.