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.

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.

In X.Org Server (aka xserver and xorg-server) before 1.19.4, an attacker authenticated to an X server with the X shared memory extension enabled can cause aborts of the X server or replace shared memory segments of other X clients in the same session.

In X.Org Server (aka xserver and xorg-server) before 1.19.4, a local attacker authenticated to the X server could overflow a global buffer, causing crashes of the X server or potentially other problems by injecting large or malformed XKB related atoms and accessing them via xkbcomp.