Linux X.org MIT-SHM Extension Privilege Escalation Exploit

The MIT-SHM extension for the X.org X11 server before 1.4 is vulnerable to a buffer overflow that allows an attacker to run arbitrary code as root. The error is located in the compNewPixmap function. This module triggers the overflow while creating a window with a high bit depth and a second child window with a lower bit depth. The overflow is only possible when windows of different depth can be created on the display, so most servers on 24 or 32 bit modes are not vulnerable, because the X server usually stores 24 bit pixels in 4 bytes. After successful exploitation an agent will be installed with root privileges.