The remote host is missing an update to libtk-img announced via advisory DSA 1598-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201598-1

It was discovered that a buffer overflow in the GIF image parsing code of Tk, a cross-platform graphical toolkit, could lead to denial of service and potentially the execution of arbitrary code. For the stable distribution (etch), this problem has been fixed in version 1:1.3-15etch2. For the unstable distribution (sid), this problem has been fixed in version 1:1.3-release-7. We recommend that you upgrade your libtk-img package.