The mod_dialback module in Prosody before 0.9.9 does not properly generate random values for the secret token for server-to-server dialback authentication, which makes it easier for attackers to spoof servers via a brute force attack.
https://prosody.im/security/advisory_20160108-2/
https://prosody.im/issues/issue/571
http://www.openwall.com/lists/oss-security/2016/01/08/5
http://www.debian.org/security/2016/dsa-3439
http://lists.fedoraproject.org/pipermail/package-announce/2016-January/175868.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-January/175829.html