It was discovered that libXdmcp before 1.1.2 including used weak entropy to generate session keys. On a multi-user system using xdmcp, a local attacker could potentially use information available from the process list to brute force the key, allowing them to hijack other users' sessions.

A flaw was found in the way xserver memory was not properly initialized. This could leak parts of server memory to the X client. In cases where Xorg server runs with elevated privileges, this could result in possible ASLR bypass. Xorg-server before version 1.20.9 is vulnerable.