The xf86 package contains various libraries and programs which are fundamental for the X server to function. The libX11.so library from this package dynamically loads other libraries where the pathname is controlled by the user invoking the program linked against libX11.so. Unfortunately, libX11.so also behaves the same way when linked against setuid programs. This behavior allows local users to execute arbitrary code under a different UID which can be the root-UID in the worst case. libX11.so has been fixed to check for calls from setuid programs. It denies loading of user controlled libraries in this case. We recommend an update in any case since there is no easy workaround possible except removing the setuid bit from any program linked against libX11.so.