X.Org X Window System (aka X11 and X) X11R5 and X.Org Server (aka xserver and xorg-server) before 1.16.3, when using SUN-DES-1 (Secure RPC) authentication credentials, does not check the return value of a malloc call, which allows remote attackers to cause a denial of service (NULL pointer dereference and server crash) via a crafted connection request.