The remote host is missing an update to imlib2 announced via advisory DSA 552-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20552-1

Marcus Meissner discovered a heap overflow error in imlib2, an imaging library for X and X11 and the successor of imlib, that may be utilised by an attacker to execute arbitrary code on the victims machine. For the stable distribution (woody) this problem has been fixed in version 1.0.5-2woody1. For the unstable distribution (sid) this problem has been fixed in version 1.1.0-12.4. We recommend that you upgrade your imlib2 packages.