1.5 - 20180502

This is a features release. Updated binaries will be available shortly.


  • Fix memory leak that could be caused by a malicious CONNECT packet. This does not yet have a CVE assigned. Closes #533493 (on Eclipse bugtracker)

Broker features

  • Add per_listener_settings to allow authentication and access control to be per listener.
  • Add limited support for reloading listener settings. This allows settings for an already defined listener to be reloaded, but port numbers must not be changed.
  • Add ability to deny access to SUBSCRIBE messages as well as the current read/write accesses. Currently for auth plugins only.
  • Reduce calls to malloc through the use of UHPA.
  • Outgoing messages with QoS>1 are no longer retried after a timeout period. Messages will be retried when a client reconnects. This change in behaviour can be justified by considering when the timeout may have occurred.
  • If a connection is unreliable and has dropped, but without one end noticing, the messages will be retried on reconnection. Sending additional PUBLISH or PUBREL would not have changed anything.
  • If a client is overloaded/unable to respond/has a slow connection then sending additional PUBLISH or PUBREL would not help the client catch up. Once the backlog has cleared the client will respond. If it is not able to catch up, sending additional duplicates would not help either.
  • Add use_subject_as_username option for certificate based client authentication to use the entire certificate subject as a username, rather than just the CN. Closes #469467.
  • Change sys tree printing output. This format shouldn't be relied upon and may change at any time. Closes #470246.
  • Minimum supported libwebsockets version is now 1.3.
  • Add systemd startup notification and services. Closes #471053.
  • Reduce unnecessary malloc and memcpy when receiving a message and storing it. Closes #470258.
  • Support for Windows XP has been dropped.
  • Bridge connections now default to using MQTT v3.1.1.
  • mosquitto_db_dump tool can now output some stats on clients.
  • Perform utf-8 validation on incoming will, subscription and unsubscription topics.
  • new $SYS/broker/store/messages/count (deprecates $SYS/broker/messages/stored)
  • new $SYS/broker/store/messages/bytes
  • max_queued_bytes feature to limit queues by real size rather than than just message count. Closes Eclipse #452919 or Github #100
  • Add support for bridges to be configured to only send notifications to the local broker.
  • Add set_tcp_nodelay option to allow Nagle's algorithm to be disabled on client sockets. Closes #433.
  • The behaviour of allow_anonymous has changed. In the old behaviour, the default if not set was to allow anonymous access. The new behaviour is to default is to allow anonymous access unless another security option is set. For example, if password_file is set and allow_anonymous is not set, then anonymous access will be denied. It is still possible to allow anonymous access by setting it explicitly.

Broker fixes

  • Fix UNSUBSCRIBE with no topic is accepted on MQTT 3.1.1. Closes #665.
  • Produce an error if two bridges share the same local_clientid.
  • Miscellaneous fixes on Windows.
  • queue_qos0_messages was not observing max_queued_** limits
  • When using the include_dir configuration option sort the files alphabetically before loading them. Closes #17.
  • IPv6 is no longer disabled for websockets listeners.
  • Remove all build timestamp information including $SYS/broker/timestamp. Closes #651.
  • Correctly handle incoming strings that contain a NULL byte. Closes #693.
  • Use constant time memcmp for password comparisons.
  • Fix incorrect PSK key being used if it had leading zeroes.
  • Fix memory leak if a client provided a username/password for a listener with use_identity_as_username configured.
  • Fix use_identity_as_username not working on websockets clients.
  • Don't crash if an auth plugin returns MOSQ_ERR_AUTH for a username check on a websockets client. Closes #490.
  • Fix 08-ssl-bridge.py test when using async dns lookups. Closes #507.
  • Lines in the config file are no longer limited to 1024 characters long. Closes #652.
  • Fix $SYS counters of messages and bytes sent when message is sent over a Websockets. Closes #250.
  • Fix upgrade_outgoing_qos for retained message. Closes #534.
  • Fix CONNACK message not being sent for unauthorised connect on websockets. Closes #8.
  • Maximum connections on Windows increased to 2048.
  • When a client with an in-use client-id connects, if the old client has a will, send the will message. Closes #26.
  • Fix parsing of configuration options that end with a space. Closes #804.

Client library features

  • Outgoing messages with QoS>1 are no longer retried after a timeout period. Messages will be retried when a client reconnects.
  • DNS-SRV support is now disabled by default.
  • Add mosquitto_subscribe_simple() This is a helper function to make retrieving messages from a broker very straightforward. Examples of its use are in examples/subscribe_simple.
  • Add mosquitto_subscribe_callback() This is a helper function to make processing messages from a broker very straightforward. An example of its use is in examples/subscribe_simple.
  • Connections now default to using MQTT v3.1.1.
  • Add mosquitto_validate_utf8() to check whether a string is valid UTF-8 according to the UTF-8 spec and to the additional restrictions imposed by the MQTT spec.
  • Topic inputs are checked for UTF-8 validity.
  • Add mosquitto_userdata function to allow retrieving the client userdata member variable. Closes #111.
  • Add mosquitto_pub_topic_check2(), mosquitto_sub_topic_check2(), and mosquitto_topic_matches_sub2() which are identical to the similarly named functions but also take length arguments.
  • Add mosquitto_connect_with_flags_callback_set(), which allows a second connect callback to be used which also exposes the connect flags parameter. Closes #738 and #128.
  • Add MOSQ_OPT_SSL_CTX option to allow a user specified SSL_CTX to be used instead of the one generated by libmosquitto. This allows greater control over what options can be set. Closes #715.
  • Add MOSQ_OPT_SSL_CTX_WITH_DEFAULTS to work with MOSQ_OPT_SSL_CTX and have the default libmosquitto SSL_CTX configuration applied to the user provided SSL_CTX. Closes #567.

Client library fixes

  • Fix incorrect PSK key being used if it had leading zeroes.
  • Initialise "result" variable as soon as possible in mosquitto_topic_matches_sub. Closes #654.
  • No need to close socket again if setting non-blocking failed. Closes #649.
  • Fix mosquitto_topic_matches_sub() not correctly matching foo/bar against foo/+/#. Closes #670.
  • SNI host support added.

Client features

  • Add -F to mosquitto_sub to allow the user to choose the output format.
  • Add -U to mosquitto_sub for unsubscribing from topics.
  • Add -c (clean session) to mosquitto_pub.
  • Add --retained-only to mosquitto_sub to exit after receiving all retained messages.
  • Add -W to allow mosquitto_sub to stop processing incoming messages after a timeout.
  • Connections now default to using MQTT v3.1.1.
  • Default to using port 8883 when using TLS.
  • mosquitto_sub doesn't continue to keep connecting if CONNACK tells it the connection was refused.

Client fixes

  • Correctly handle empty files with mosquitto_pub -l. Closes #676.


  • Add WITH_STRIP option (defaulting to "no") that when set to "yes" will strip executables and shared libraries when installing.
  • Add WITH_STATIC_LIBRARIES (defaulting to "no") that when set to "yes" will build and install static versions of the client libraries.
  • Don't run TLS-PSK tests if TLS-PSK disabled at compile time. Closes #636.
  • Support for openssl versions 1.0.0 and 1.0.1 has been removed as these are no longer supported by openssl.


  • Replace mentions of deprecated c_rehash with openssl rehash.