This is a security and bugfix release.


If a client connects using MQTT v5, will a Will message that has MQTT v5 properties attached, and the very first Will property is one of content-type, correlation-data, payload-format-indicator, or response-topic, then at the point the client disconnects, the broker will attempt to read from freed memory, resulting in a possible crash.


  • Fix memory access after free, leading to possible crash, when v5 client with Will message disconnects, where the Will message has as its first property one of content-type, correlation-data, payload-format-indicator, or response-topic. Closes #1244.
  • Fix build for WITH_TLS=no. Closes #1250.
  • Fix Will message not allowing user-property properties.
  • Fix broker originated messages (e.g. $SYS/broker/version) not being published when check_retain_source set to true. Closes #1245.
  • Fix $SYS/broker/version being incorrectly expired after 60 seconds. Closes #1245.


  • Fix crash after client has been unable to connect to a broker. This occurs when the client is exiting and is part of the final library cleanup routine. Closes #1246.


  • Fix -L url parsing. Closes [#1248].