wolfMQTT v2.1.0 (02JUL2026)

v2.1.0 (07/02/2026)

Release 2.1.0 has been developed according to wolfSSL's development and QA
process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• New Features

  • wolfMQTT Broker session persistence: pluggable persistence hooks via
    MqttBroker_SetPersistHooks with a POSIX backend
    (MqttBrokerNet_PersistPosix_Init / MqttBrokerNet_PersistPosix_Free),
    message ordering, an offline message queue, and AES-GCM encryption of
    persisted state at rest (#538)
  • New packet-validation helpers: MqttPacket_TopicNameValid,
    MqttPacket_TopicFilterValid, MqttPacket_TopicFilterIsWildcard,
    MqttPacket_FixedHeaderFlagsValid, and MqttPacket_SubAckReturnCodeValid
    (#552)
  • WOLFMQTT_MAX_QOS build cap to compile out the QoS 2 state machine and
    advertise v5 MAX_QOS in CONNACK (#537)

• Security Hardening

  • Reject ill-formed UTF-8 in MQTT UTF-8 string fields per [MQTT-1.5.3-1].
    MqttDecode_String now validates each decoded string against RFC 3629
    and rejects encodings of surrogate code points (U+D800..U+DFFF) with
    MQTT_CODE_ERROR_MALFORMED_DATA. Receivers MUST close the network
    connection on malformed packets, which the broker's existing decode-
    error path enforces. The check covers ClientId, Will Topic, Topic Name,
    Topic Filter, Username, and v5 STRING/STRING_PAIR property values.
  • The broker now requires auth_user and auth_pass to be configured as
    a pair. Previously, setting only one (e.g. the -u CLI flag without
    -P) silently enabled single-factor authentication: the unconfigured
    side was never checked, so any password authenticated against a matching
    username (or any username against a matching password). MqttBroker_Start
    now rejects a partial credential configuration with
    MQTT_CODE_ERROR_BAD_ARG, and the connect-time gate fails closed as a
    defense in depth if only one credential is set. Leaving both NULL still
    disables authentication.

• API / Behavior Changes

  • MqttDecode_String may now return MQTT_CODE_ERROR_MALFORMED_DATA
    on ill-formed UTF-8. This applies to client builds as well as broker
    builds — [MQTT-1.5.3-1] is normative for both. wolfMQTT clients that
    previously accepted PUBLISH messages with non-UTF-8 topics from
    misbehaving brokers will now error on those messages. There is no
    opt-out: the spec is a MUST.
  • MqttDecode_Publish now propagates the underlying error from
    MqttDecode_String (e.g. MALFORMED_DATA) instead of always
    returning MQTT_CODE_ERROR_OUT_OF_BUFFER on topic decode failure.
  • MqttDecode_Props similarly now propagates the underlying error from
    MqttDecode_String for v5 STRING and STRING_PAIR property types
    (Reason String, Content Type, User Property, etc.) instead of masking
    it as MQTT_CODE_ERROR_PROPERTY.
  • The CONNECT Password decode no longer goes through MqttDecode_String
    because [MQTT-3.1.3.5] defines Password as Binary Data, not a UTF-8
    string. A binary password containing bytes that are not valid UTF-8
    (e.g., 0xC0, 0xFF) would otherwise be incorrectly rejected.
  • MqttClient_Publish / MqttClient_Publish_ex now return the new
    MQTT_CODE_ERROR_PUBLISH_REJECTED (-21) when a v5 broker rejects a
    QoS>0 PUBLISH via a PUBACK (QoS 1), PUBREC, or PUBCOMP (QoS 2) reason
    code >= 0x80 (e.g. Not authorized, Quota exceeded, Topic Name invalid,
    Payload format invalid). Previously these were reported as
    MQTT_CODE_SUCCESS, so the application proceeded as if the broker had
    accepted the message. The specific reason is available in
    MqttPublish.resp.reason_code. For QoS 2, a PUBREC reason code >= 0x80
    now ends the exchange without sending PUBREL per [MQTT-4.3.3] instead of
    timing out. v3.1.1 publishes are unaffected, as is the return value of
    the fire-and-forget MqttClient_Publish_WriteOnly call itself. Callers
    that treat any non-success return as fatal may need to handle this code.
    In WOLFMQTT_MULTITHREAD builds where a dedicated thread drives reads,
    that reading thread now returns MQTT_CODE_ERROR_PUBLISH_REJECTED when it
    processes a QoS 2 PUBREC rejection (instead of advancing the handshake
    with an illegal PUBREL); the originating write-only publish's pending
    response is not auto-completed in that case, so it blocks until
    cmd_timeout_ms. A QoS 1 PUBACK or QoS 2 PUBCOMP rejection is NOT
    detected on the write-only path (the publish appears successful), matching
    prior behavior; use MqttClient_Publish/_ex for reliable detection.
  • An incoming PUBLISH received by a client with no message callback
    registered (msg_cb == NULL) now returns MQTT_CODE_ERROR_CALLBACK
    (-13) instead of MQTT_CODE_SUCCESS. Previously the payload was silently
    read and discarded, and for QoS 1/2 a PUBACK/PUBREC was still sent,
    falsely telling the broker the message was delivered while the application
    never saw it. MqttClient_HandlePacket no longer populates an ACK in this
    case, so no false acknowledgement is sent. This affects standard MQTT
    (MqttClient_Publish_ReadPayload) and MQTT-SN (SN_Client_HandlePacket).
    A registered msg_cb is now required to receive a PUBLISH; this includes
    the receive-into-object pattern via MqttClient_WaitMessage_ex /
    SN_Client_WaitMessage_ex, which previously returned success after
    decoding into the caller-supplied object without a callback. A NULL
    callback is still valid for a publish-only client that never receives
    messages; the error surfaces only if such a client is actually pushed a
    PUBLISH. The built-in broker is unaffected (it handles incoming PUBLISH
    through its own path, not this one).

• Fixes

  • SN_Client_Unsubscribe now registers its pending UNSUBACK response under
    the real Packet Identifier instead of a hard-coded 0. In
    WOLFMQTT_MULTITHREAD builds where a dedicated reader thread processes the
    UNSUBACK first, MqttClient_RespList_Find matches on the decoded packet
    id, so the id-0 entry never matched and the response was consumed into the
    generic object, leaving the unsubscribing thread blocked until
    cmd_timeout_ms. The registration now matches SN_Client_Subscribe,
    SN_Client_Register, and SN_Client_Publish.

• What's Changed

  • Fix BrokerHandle_Connect null check (#477)
  • Fenrir fixes (#478)
  • Add testing validation and fixes for wolfMQTT (#480)
  • Replace deprecated VeriSign CA with Amazon Root CA 1 + Starfield G2 (#481)
  • Update testing with a more flexible framework (#482)
  • Fix new Fenrir reports (#483)
  • Always check MqttDecode_Num's return code (#479)
  • Add Fenrir suggested test cases (#484)
  • Reject null chars in strings (#503)
  • Fix various spec compliance gaps (#504)
  • Fix MQTTv5 QoS 2 CONNACK interop and add WOLFMQTT_MAX_QOS build cap (#537)
  • Fix Coverity nightly: inline action, drop broken md5 hash lookup (#547)
  • Harden param checks in MqttDecode_FixedHeader and MqttDecode_ConnectAck (#546)
  • Harden Coverity tool download: curl -L --fail + gzip sanity check (#549)
  • Fix broker disconnect to better handle SIGPIPE (#548)
  • wolfMQTT broker: ordering, persistence, offline queue, AES-GCM at rest (#538)
  • Speed up CI and stabilize aws-ca-regression (#551)
  • MQTT-SN fixes (#550)
  • Broker, client, and MQTT v5 packet validation and reliability fixes (#552)
  • Fenrir fixes (#554)

• New Contributors

  • @night1rider made their first contribution (#481)

wolfMQTT v2.0.0 (20MAR2026)

v2.0.0 (03/20/2026)

Release 2.0.0 has been developed according to wolfSSL's development and QA
process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• New Features

  • Lightweight MQTT Broker — New built-in MQTT broker implementation (#457)
  • MQTT v3.1.1 spec compliance checks (#462)
  • Secure and non-secure port listening support (#465)
  • WebSocket transport support (#466)
  • wolfIP (embedded TCP/IP stack) support (#463)
  • Retained messages, session persistence, graceful disconnect, QoS subscription updates (#465)
  • libFuzzer-based broker fuzzing infrastructure (#474)
  • wolfIP Integration — Added wolfIP support for both MQTT client and broker (#463)
  • lastError Field — Preserve TLS error code via new lastError in the network context (#458)

• Bug Fixes

  • Fix race condition in wm_SemLock (#475)
  • Fix wildcard topic matching (#472)
  • Fix LWT (Last Will and Testament) length checks and payload free issues (#472, #473)
  • Fix subAck buffer size check and topic count validation (#472)
  • Fix MqttPacket_Write failure return handling (#473)
  • Fix MQTT-SN: null pointer dereference, non-blocking read, encode/decode issues (#473)
  • Fix MqttDecode_Auth reason code issue (#473)
  • Fix broker client connect status check (#472)
  • Fix SN_Client_WaitType issues (#456)
  • Fix curl transport: use internal loops for partial read/write handling (#459)

• Security Hardening

  • Add overflow checks in network and socket IO (#467)
  • Add checks for negative return values in MqttDecode_String calls (#467)
  • Add encoding error checks (#467)
  • Add remain_len validation check (#471)
  • Static analysis fixes for MqttClient_Auth, MqttProps_Add, MqttDecode_SubscribeAck, MqttDecode_Props (#469)
  • Static analysis fixes for SN_Decode_Register, SN_Decode_GWInfo, SN_Client_WillTopicUpdate, SN_Encode_Publish, SN_Encode_RegAck, SN_Client_Connect (#468)
  • Add debug warning when using VERIFY_NONE (#475)

• CI / Testing

  • Add CI workflows for codespell, multi-compiler, and sanitizer tests (#470)
  • Add Coverity workflow schedule (#450, #451)
  • Add WebSocket broker configurations to CI (#466)
  • Expanded broker edge case testing (#465)
  • Improved broker test execution speed (#465)

• Other

  • Updated client certificates (#455)
  • Added wolfSSL as submodule option (#452)

wolfMQTT v1.21.0 (03DEC2025)

Release 1.21.0 has been developed according to wolfSSL's development and QA
process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

What's Changed

• Add port for NETX use by @JacobBarthelmeh in #427
• Fix heap buffer overflow in MqttDecode_Num with bounds checking by @devin-ai-integration[bot] in #430
• Restore instructions for testing against OQS mosquitto integration. by @anhu in #432
• initial threadx test by @JacobBarthelmeh in #429
• Rename ML-KEM hybrids to match IETF Draft. by @anhu in #435
• Update expired test certs by @lealem47 in #441
• Pin to ESP-IDF v5.5, limit workflow push branches, line endings by @gojimmypi in #444
• Fix: MQTT v5 Property-Packet Protocol Validation and Decode Safety by @kaabia in #440
• Fix: Correct state transition check in MqttClient_Auth by @kaabia in #439
• fix: correct variable in MQTT property decode error checks by @kaabia in #445
• Add fflush to mqtt-sub example by @embhorn in #447
• Update license to GPLv3 by @embhorn in #448

wolfMQTT v1.20.0 (02MAY2025)

v1.20.0 (05/02/2025)

Release 1.20.0 has been developed according to wolfSSL's development and QA
process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• OQS's Mosquitto is out of date. by @anhu in #417
• Add support for websocket by @embhorn in #418
• Add support for secure websockets by @embhorn in #419
• Add secure ws CI test by @embhorn in #421
• Update examples for latest Managed Components by @gojimmypi in #420
• Improve cmake duplicate component check by @gojimmypi in #422

wolfMQTT v1.19.2 (31JAN2025)

v1.19.2 (01/31/2025)

Release 1.19.2 has been developed according to wolfSSL's development and QA
process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• Handle connection error in mqttsimple client by @embhorn in #407
• Fix stat reset for ping response by @embhorn in #414

wolfMQTT v1.19.1 (06NOV2024)

v1.19.1 (11/06/2024)

Release 1.19.1 has been developed according to wolfSSL's development and QA process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• wolfssl 5.7.2 time_helper type adjustments for Espressif example by @gojimmypi in #404
• Fix Doxygen issues by @embhorn in #403

wolfMQTT v1.19.0 (22MAR2024)

v1.19.0 (3/22/2024)
Release 1.19.0 has been developed according to wolfSSL's development and QA process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• Add stress test. by @philljj in #387
• Add cmake CI test and fix pthread detection by @embhorn in #389
• Initial wolfMQTT Espressif ESP32 template and AWS IoT examples by @gojimmypi in #388
• Add curl test dependencies by @lealem47 in #392
• Improving and fixing typos for STM32CUBE build by @lealem47 in #391
• Fix string prop OOB read by @embhorn in #394
• Fix some Helgrind thread errors with enable-tls, and enable-curl. by @philljj in #396
• Initial Espressif CI; limit Zepher CI by @gojimmypi in #390
• Fix double unlock and double lock in multithread example. by @philljj in #397
• Fix double lock of lockRecv. by @philljj in #398

wolfMQTT v1.18.0 (22DEC2023)

v1.18.0 (12/22/2023)

Release 1.18.0 has been developed according to wolfSSL's development and QA process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• Add curl easy socket backend. by @philljj in #380
• WOLFMQTT_EXAMPLE_CERT allowing static or extern cert assignment by @gojimmypi in #354
• Tiny readme cleanup. by @philljj in #381
• Fix high coverity issues by @embhorn in #379
• Add broker check to scripts by @embhorn in #385
• Cmake build fixes by @embhorn in #384

wolfMQTT v1.17.1 (29NOV2023)

v1.17.1 (11/29/2023)

Release 1.17.1 has been developed according to wolfSSL's development and QA process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• Include stdint.h in userio_template.h by @lealem47 in #371
• Improvements to multithread locking and tests. by @dgarske in #369
• Cleanup executable status on src files. by @philljj in #372
• Close socket on error in NetConnect by @embhorn in #375
• Fixes for non-blocking with larger payload and improvements to the test and examples by @dgarske in #373
• Add MQTT-SN CI tests by @embhorn in #376
• Fix Wild read in MqttProps_Free by @embhorn in #377
• Fix fuzzer issues in MqttDecode_Props by @embhorn in #378

wolfMQTT v1.17.0 (02NOV2023)

v1.17.0 (11/2/2023)

Release 1.17.0 has been developed according to wolfSSL's development and QA process (see link below) and successfully passed the quality criteria.
https://www.wolfssl.com/about/wolfssl-software-development-process-quality-assurance

• Fix for declaration after executable block by @lealem47 in #341
• Add QNX IDE, Makefile, and remove source code exec bit by @JacobBarthelmeh
  in #317
• update for cmake after wolfssl added NAMESPACE by @JacobBarthelmeh in #343
• Add mutex protection to MqttClient_NetDisconnect by @embhorn in #342
• Add DTLS support to MQTT-SN client by @embhorn in #348
• Tie zephyr tests to a release by @julek-wolfssl in #350
• add documentation link to README by @gojimmypi in #355
• Possible patch for POSIX conditional wait issue by @dgarske in #356
• Fix publish with topic ID >=127 by @embhorn in #351
• Adding publish and subscribe atomic client examples by @embhorn in #347
• Allow disabling the posix conditional signal by @dgarske in #360
• Exclude CI tests with external brokers by @embhorn in #362
• Improvements for client property stack by @dgarske in #361
• Add mosquitto to CI tests by @embhorn in #365
• Fixes for non-blocking edge cases by @dgarske in #363
• Refactor MQTT-SN code by @embhorn in #366