The remote Debian host is missing a security-related update.
Brad Hill of iSEC Partners discovered that many XML implementations are vulnerable to external entity expansion issues, which can be used for various purposes such as firewall circumvention, disguising an IP address, and denial-of-service. libxml2 was susceptible to these problems when performing string substitution during entity expansion.
Upgrade the libxml2 packages. For the stable distribution (squeeze), these problems have been fixed in version 2.7.8.dfsg-2+squeeze7.