In the X.Org X server before 2017-06-19, a user authenticated to an X Session could crash or execute code in the context of the X Server by exploiting a stack overflow in the endianness conversion of X Events.
https://cgit.freedesktop.org/xorg/xserver/commit/?id=ba336b24052122b136486961c82deac76bbde455
https://cgit.freedesktop.org/xorg/xserver/commit/?id=8caed4df36b1f802b4992edcfd282cbeeec35d9d
https://cgit.freedesktop.org/xorg/xserver/commit/?id=215f894965df5fb0bb45b107d84524e700d2073c
https://bugzilla.suse.com/show_bug.cgi?id=1035283