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.
Prosody before 0.9.4 does not properly restrict the processing of compressed XML elements, which allows remote attackers to cause a denial of service (resource consumption) via a crafted XMPP stream, aka an "xmppbomb" attack, related to core/portmanager.lua and util/xmppstream.lua.