The remote host is missing an update to xen announced via advisory DSA 2531-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202531-1

Several denial-of-service vulnerabilities have been discovered in Xen, the popular virtualization software. The Common Vulnerabilities and Exposures project identifies the following issues: CVE-2012-3432 Guest mode unprivileged code, which has been granted the privilege to access MMIO regions, may leverage that access to crash the whole guest. Since this be used to crash a client from within, this vulnerability is consider with low impact. CVE-2012-3433 A guest kernel can cause the host to become unresponsive for a period of time, potentially leading to a DoS. Since an attacker with full control in the guest can impact on the host, this vulnerability is consider with high impact. For the stable distribution (squeeze), this problem has been fixed in version 4.0.1-5.3. For the unstable distribution (sid), this problem has been fixed in version 4.1.3-1. We recommend that you upgrade your xen packages.