The remote host is missing an update to smartlist announced via advisory DSA 720-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20720-1

Jeroen van Wolffelaar noticed that the confirm add-on of SmartList, the listmanager used on lists.debian.org, which is used on that host as well, could be tricked to subscribe arbitrary addresses to the lists. For the stable distribution (woody) this problem has been fixed in version 3.15-5.woody.1. For the unstable distribution (sid) this problem has been fixed in version 3.15-18. We recommend that you upgrade your smartlist package.