It was just last month that there was an X.Org Server security issue
dealing with hot-plugging of input devices. Being announced today is a new round of security problems, this time multiple issues dealing with X.Org client libraries.
Alan Coopersmith of Oracle and X.Org veteran publicly shared the discovered security problems
Ilja van Sprundel, a security researcher with IOActive, has discovered a large number of issues in the way various X client libraries handle the responses they receive from servers, and has worked with X.Org's security team to analyze, confirm, and fix these issues.
Most of these issues stem from the client libraries trusting the server to send correct protocol data, and not verifying that the values will not overflow or cause other damage. Most of the time X clients & servers are run by the same user, with the server more privileged from the clients, so this is not a problem, but there are scenarios in which a privileged client can be connected to an unprivileged server, for instance, connecting a setuid X client (such as a screen lock program) to a virtual X server (such as Xvfb or Xephyr) which the user has modified to return invalid data, potentially allowing the user to escalate their privileges.
The X.Org security team would like to take this opportunity to remind X client authors that current best practices suggest separating code that requires privileges from the GUI, to reduce the attack surface of issues like this.
The noted security vulnerabilities come down to integer overflows calculating memory needs for replies, sign extension issues, buffer overflows from not validating length or offset values, integer overflows parsing user-specified files, and memory corruption due to unchecked return values.
There are issues concerning libX11, libXext, libXfices, LibXi, libXinerama, LibXp, libXrandr, libXrender, libXRes, libXtst, libXv, libXvMC, libXxf86dga, libdmx, libxcb, libGLX, libchromeXvMC, libFS, libXcursor, and libXt. Fortunately, X.Org developers are preparing new packages for all of these X.Org libraries to mitigate these security vulnerabilities.