The SASL negotiation in Jabber Studio jabberd before 2.0s11 allows remote attackers to cause a denial of service ("c2s segfault") by sending a "response stanza before an auth stanza".
The expat XML parser code, as used in the open source Jabber (jabberd) 1.4.3 and earlier, jadc2s 0.9.0 and earlier, and possibly other packages, allows remote attackers to cause a denial of service (application crash) via a malformed packet to a socket that accepts XML connections.