plugins/mod_compression.lua in (1) Prosody before 0.9.4 and (2) Lightwitch Metronome through 3.4 negotiates stream compression while a session is unauthenticated, which allows remote attackers to cause a denial of service (resource consumption) via compressed XML elements in an XMPP stream, aka an "xmppbomb" attack.
http://www.debian.org/security/2014/dsa-2895
http://secunia.com/advisories/57710
http://openwall.com/lists/oss-security/2014/04/09/1