The remote host is missing an update to libnss-ldap announced via advisory DSA 1430-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201430-1

It was reported that a race condition exists in libnss-ldap, an NSS module for using LDAP as a naming service, which could cause denial of service attacks when applications use pthreads. This problem was spotted in the dovecot IMAP/POP server but potentially affects more programs. For the stable distribution (etch), this problem has been fixed in version 251-7.5etch1. For the old stable distribution (sarge), this problem has been fixed in version 238-1sarge1. For the unstable distribution (sid), this problem has been fixed in version 256-1. We recommend that you upgrade your libnss-ldap package.