The remote host is missing an update to netkit-telnet announced via advisory DSA 556-2.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20556-2

This is an update for DSA 556-1 which was intended to fix a denial of service situation in netkit-telnet but didn't. The update for unstable did fix the problem. For completeness below is the original advisory text: Michal Zalewski discovered a bug in the netkit-telnet server (telnetd) whereby a remote attacker could cause the telnetd process to free an invalid pointer. This causes the telnet server process to crash, leading to a straightforward denial of service (inetd will disable the service if telnetd is crashed repeatedly), or possibly the execution of arbitrary code with the privileges of the telnetd process (by default, the 'telnetd' user). For the unstable distribution (sid) this problem has been fixed in version 0.17-26. For the stable distribution (woody) this problem has been fixed in version 0.17-18woody2. We recommend that you upgrade your netkit-telnet-ssl package.