It was discovered that a race condition in the init.d script of the X Font Server allows the modification of file permissions of arbitrary files if the local administrator can be tricked into restarting the X font server.
For the oldstable distribution (sarge) xfs is present as part of the monolithic xfree86 package. A fix will be provided along with a future security update.
For the stable distribution (etch) this problem has been fixed in version 1.0.1-6.
For the unstable distribution (sid) this problem has been fixed in version 1.0.4-2.
We recommend that you upgrade your xfs package.
MD5 checksums of the listed files are available in the original advisory.