The remote host is missing an update to zlib announced via advisory DSA 763-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20763-1

Markus Oberhumer discovered a flaw in the way zlib, a library used for file compression and decompression, handles invalid input. This flaw can cause programs which use zlib to crash when opening an invalid file. This problem does not affect the old stable distribution (woody). For the current stable distribution (sarge), this problem has been fixed in version 1.2.2-4.sarge.2. For the unstable distribution (sid), this problem has been fixed in version 1.2.3-1. We recommend that you upgrade your zlib package.