Published: 15 December 2011
The X.Org X wrapper (xserver-wrapper.c) in Debian GNU/Linux and Ubuntu Linux does not properly verify the TTY of a user who is starting X, which allows local users to bypass intended access restrictions by associating stdin with a file that is misinterpreted as the console TTY.
requires pty access. In combination with CVE-2011-4029 this becomes more important, but that CVE is fixed in Ubuntu.
Debian fixed this by dropping support for alternate TTY devices, which we need for upstart support. See changelog for (1:7.4~2ubuntu2) and (1:7.4~4).