Back in October there was a X11 security advisory going back to 1993 and today's noted security issue was for code introduced in May of 1991. This security advisory comes just days after the X Server security was called a disaster with what will amount to at least hundreds of open security issues found by a researcher.
The security was found via running the cppcheck utility as a static analyzer to look at the code. The issue found is a stack buffer overflow in the passing of BDF font files in libXfont. It's an issue present for more than two decades and was easily spotted with static analysis of the code. When a buffer overflow does happen in libXfont, it's possible that the bug could lead to an unprivileged user acquiring root access to the system.
This bug has been found in every X Server release going back to X11R5 and was corrected with the new release of libXfont 1.4.6. More details on this latest security advisory can be found via the xorg-announce list.