The remote host is missing an update to l2tpd announced via advisory DSA 530-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20530-1

Thomas Walpuski reported a buffer overflow in l2tpd, an implementation of the layer 2 tunneling protocol, whereby a remote attacker could potentially cause arbitrary code to be executed by transmitting a specially crafted packet. The exploitability of this vulnerability has not been verified. For the current stable distribution (woody), this problem has been fixed in version 0.67-1.2. For the unstable distribution (sid), this problem has been fixed in version 0.70-pre20031121-2. We recommend that you update your l2tpd package.