Ilja van Sprundel, the security researcher at IOActive who uncovered lots of X.Org security issues last year and criticzed the Linux desktop security in many parts of the open-source desktop stack, is the one who uncovered these latest security vulnerabilities. It was back in December that this same researcher said the X.Org Server security is a disaster and it's even worse than it looks.
Alan Coopersmith on the behalf of X.Org Security Response Team acknowledged this new round of issues in a X.Org Security Advisory sent out a few minutes ago. "Most of these issues stem from libXfont trusting the font server to send valid protocol data, and not verifying that the values will not overflow or cause other damage. This code is commonly called from the X server when an X Font Server is active in the font path, so may be running in a setuid-root process depending on the X server in use. Exploits of this path could be used by a local, authenticated user to attempt to raise privileges; or by a remote attacker who can control the font server to attempt to execute code with the privileges of the X server."
As with most of these vulnerabilities, these issues affect all versions of the X font library going back many years... To X11R5 that was released in 1991. Today's security problems are reported as CVE-2014-0209: integer overflow of allocations in font metadata file parsing, CVE-2014-0210: unvalidated length fields when parsing xfs protocol replies, and CVE-2014-0211: integer overflows calculating memory needs for xfs replies. For those using libXfont, patches are available to fix these issues via Git.