Improper Neutralization Affecting io.netty:netty-codec-mqtt package, versions [,4.1.137.Final)[4.2.0.Final, 4.2.17.Final)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JAVA-IONETTY-19256586
- published25 Aug 2026
- disclosed24 Aug 2026
- creditUnknown
Introduced: 24 Aug 2026
NewCVE-2026-76816 (opens in a new tab)How to fix?
Upgrade io.netty:netty-codec-mqtt to version 4.1.137.Final, 4.2.17.Final or higher.
Overview
Affected versions of this package are vulnerable to Improper Neutralization through the CONNECT and PUBLISH encoding paths in MqttEncoder and MqttCodecUtil. An attacker can send MQTT fields containing NUL bytes or wildcard characters by supplying crafted client identifiers, usernames, will topics, or publish topic names. The encoder writes these strings into MQTT packets without rejecting illegal characters, so an application built on the codec can emit malformed MQTT messages that brokers interpret differently from the application’s own checks. In practice, this can let an attacker bypass topic or client-ID restrictions and publish to unintended topics or connect under a colliding identifier, breaking access controls and session isolation.