The remote host is missing an update to tcpreen announced via advisory DSA 1443-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201443-1

It was discovered that several buffer overflows in tcpreen, a tool for monitoring a TCP connection may lead to denial of service. For the stable distribution (etch), this problem has been fixed in version 1.4.3-0.1etch1. The old stable distribution (sarge) doesn't contain tcpreen. For the unstable distribution (sid), this problem has been fixed in version 1.4.3-0.3. We recommend that you upgrade your tcpreen package.