The remote host is missing an update to libgd2 announced via advisory DSA 602-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20602-1

More potential integer overflows have been found in the GD graphics library which weren't covered by our security advisory DSA 591. They could be exploited by a specially crafted graphic and could lead to the execution of arbitrary code on the victim's machine. For the stable distribution (woody) these problems have been fixed in version 2.0.1-10woody2. For the unstable distribution (sid) these problems will be fixed soon. We recommend that you upgrade your libgd2 packages.