The remote host is missing an update to linux-2.6 announced via advisory DSA 2126-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202126-1

Several vulnerabilities have been discovered in the Linux kernel that may lead to a privilege escalation, denial of service or information leak. For details, please visit the referenced security advisories. For the stable distribution (lenny), this problem has been fixed in version 2.6.26-26lenny1. We recommend that you upgrade your linux-2.6 and user-mode-linux packages.