This is a security and bugfix release.


A bug in the way that mosquitto handles authentication plugins has been identified. When using a plugin for authentication purposes, if the plugin returns MOSQ_ERR_UNKNOWN when making an authentication check, as might happen if a database was unavailable for example, then mosquitto incorrectly treats this as a successful authentication. This has the potential for unauthorised clients to access the running mosquitto broker and gain access to information to which they are not authorised. This is an important update for users of authentication plugins in mosquitto.


  • Don't allow access to clients when authenticating if a security plugin returns an application error. Fixes bug #1340782.
  • Ensure that bridges verify certificates by default when using TLS.
  • Fix possible crash when using pattern ACLs that do not include a %u and clients that connect without a username.
  • Fix subscriptions being deleted when clients subscribed to a topic beginning with a $ but that is not $SYS.
  • When a durable client reconnects, its queued messages are now checked against ACLs in case of a change in username/ACL state since it last connected.
  • Anonymous clients are no longer accidentally disconnected from the broker after a SIGHUP.
  • Fix bug #1324411, which could have had unexpected consequences for delayed messages in rare circumstances.

Client library

  • Fix topic matching edge case.
  • Fix callback deadlocks after calling mosquitto_disconnect(), when using the threaded interfaces. Closes bug #1313725.
  • Fix SRV support when building with CMake.


  • Use $(STRIP) for stripping binaries when installing, to allow easier cross compilation.