JabberD 2.x (aka jabberd2) before 2.6.1 allows anyone to authenticate using SASL ANONYMOUS, even when the sasl.anonymous c2s.xml option is not enabled.
https://github.com/jabberd2/jabberd2/releases/tag/jabberd-2.6.1
https://github.com/jabberd2/jabberd2/commit/8416ae54ecefa670534f27a31db71d048b9c7f16
https://bugs.debian.org/867032