ejabberd before 2.1.13 does not enforce the starttls_required setting when compression is used, which causes clients to establish connections without encryption.
The TLS driver in ejabberd before 2.1.12 supports (1) SSLv2 and (2) weak SSL ciphers, which makes it easier for remote attackers to obtain sensitive information via a brute-force attack.
The mod_pubsub module (mod_pubsub.erl) in ejabberd 2.1.8 and 3.0.0-alpha-3 allows remote authenticated users to cause a denial of service (infinite loop) via a stanza with a publish tag that lacks a node attribute.