The remote host is missing an update to libpng, libpng3 announced via advisory DSA 213-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20213-1

Glenn Randers-Pehrson discovered a problem in connection with 16-bit samples from libpng, an interface for reading and writing PNG (Portable Network Graphics) format files. The starting offsets for the loops are calculated incorrectly which causes a buffer overrun beyond the beginning of the row buffer. For the current stable distribution (woody) this problem has been fixed in version 1.0.12-3.woody.3 for libpng and in version 1.2.1-1.1.woody.3 for libpng3. For the old stable distribution (potato) this problem has been fixed in version 1.0.5-1.1 for libpng. There are no other libpng packages. For the unstable distribution (sid) this problem has been fixed in version 1.0.12-7 for libpng and in version 1.2.5-8 for libpng3. We recommend that you upgrade your libpng packages.