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.

expat_erl.c in ejabberd before 2.1.7 and 3.x before 3.0.0-alpha-3, and exmpp before 0.9.7, does not properly detect recursion during entity expansion, which allows remote attackers to cause a denial of service (memory and CPU consumption) via a crafted XML document containing a large number of nested entity references, a similar issue to CVE-2003-1564.

ejabberd_c2s.erl in ejabberd before 2.1.3 allows remote attackers to cause a denial of service (daemon crash) via a large number of c2s (aka client2server) messages that trigger a queue overload.

Cross-site scripting (XSS) vulnerability in ejabberd before 2.0.4 allows remote attackers to inject arbitrary web script or HTML via unknown vectors related to links and MUC logs.

A third-party installer generation tool, possibly BitRock InstallBuilder, as used in products including Process-one ejabberd 1.1.1_1 and earlier, generates an installer that allows local users to cause a denial of service via a symlink attack on the bitrock_installer.log temporary file. NOTE: it is possible that this vulnerability is present in other products that use this installer.