The remote host is missing an update to expat announced via advisory DSA 2525-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202525-1

It was discovered that Expat, a C library to parse XML, is vulnerable to denial of service through hash collisions and a memory leak in pool handling. For the stable distribution (squeeze), this problem has been fixed in version 2.0.1-7+squeeze1. For the testing distribution (wheezy), this problem has been fixed in version 2.1.0~beta3-1. For the unstable distribution (sid), this problem has been fixed in version 2.1.0~beta3-1. We recommend that you upgrade your expat packages.