It was discovered that the imagetops filter in cups, the Common UNIX Printing System, is prone to an integer overflow when reading malicious TIFF images.
For the oldstable distribution (etch), this problem has been fixed in version 1.2.7-4etch7.
For the stable distribution (lenny), this problem has been fixed in version 1.3.8-1lenny5.
For the testing distribution (squeeze) and the unstable distribution (sid), this problem will be fixed soon.
We recommend that you upgrade your cups packages.