The remote host is missing an update to libspf2 announced via advisory DSA 1659-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201659-1

Dan Kaminsky discovered that libspf2, an implementation of the Sender Policy Framework (SPF) used by mail servers for mail filtering, handles malformed TXT records incorrectly, leading to a buffer overflow condition (CVE-2008-2469). Note that the SPF configuration template in Debian's Exim configuration recommends to use libmail-spf-query-perl, which does not suffer from this issue. For the stable distribution (etch), this problem has been fixed in version 1.2.5-4+etch1. For the testing distribution (lenny), this problem has been fixed in version 1.2.5.dfsg-5+lenny1. For the unstable distribution (sid), this problem will be fixed soon. We recommend that you upgrade your libspf2 package.