The remote host is missing an update to imlib2 announced via advisory USN-697-1.
Details follow:
It was discovered that Imlib2 did not correctly handle certain malformed XPM and PNG images. If a user were tricked into opening a specially crafted image with an application that uses Imlib2, an attacker could cause a denial of service and possibly execute arbitrary code with the user's privileges.
Solution: The problem can be corrected by upgrading your system to the following package versions:
Ubuntu 6.06 LTS: libimlib2 1.2.1-2ubuntu0.4
Ubuntu 7.10: libimlib2 1.3.0.0debian1-4ubuntu0.2
Ubuntu 8.04 LTS: libimlib2 1.4.0-1ubuntu1.2
After a standard system upgrade you need to restart any applications that use Imlib2 to effect the necessary changes.