The remote host is missing an update as announced via advisory SSA:2007-178-01.

https://secure1.securityspace.com/smysecure/catid.html?in=SSA:2007-178-01

GD is an open source code library for the dynamic creation of images. New gd packages are available for Slackware 11.0, and -current to fix possible security issues. Please see: http://www.libgd.org/ReleaseNote020035 for complete release notes. 'Upgrading is strongly recommended.'