Uninitialized data in endianness conversion in the XEvent handling of the X.Org X Server before 2017-06-19 allowed authenticated malicious users to access potentially privileged data from the X server.
https://cgit.freedesktop.org/xorg/xserver/commit/?id=05442de962d3dc624f79fc1a00eca3ffc5489ced
https://bugzilla.suse.com/show_bug.cgi?id=1035283