CVE-2026-76816
Published:August 24, 2026
Updated:September 24, 2026
Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.137.Final and 4.2.17.Final, MqttEncoder does not validate client identifiers, will topics, usernames, and PUBLISH topic names before encoding, allowing prohibited null bytes in MQTT UTF-8 string fields and potentially causing routing, access-control, or identity mismatches in downstream brokers. The vulnerability is exploitable when an application uses Netty's MQTT encoder to construct messages from user-controlled input. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.
Affected Packages
https://github.com/netty/netty.git (GITHUB):
Affected version(s) >=netty-4.1.0.Final <netty-4.1.137.FinalFix Suggestion:
Update to version netty-4.1.137.Finalhttps://github.com/netty/netty.git (GITHUB):
Affected version(s) >=netty-4.2.0.Final <netty-4.2.17.FinalFix Suggestion:
Update to version netty-4.2.17.Finalio.netty:netty-codec-mqtt (JAVA):
Affected version(s) >=4.1.0.Final <4.1.137.FinalFix Suggestion:
Update to version 4.1.137.Finalio.netty:netty-codec-mqtt (JAVA):
Affected version(s) >=4.2.0.Final <4.2.17.FinalFix Suggestion:
Update to version 4.2.17.FinalRelated Resources (5)
Do you need more information?
Contact UsCVSS v4
Base Score:
5.1
Attack Vector
ADJACENT
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
LOW
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
LOW
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
3.5
Attack Vector
ADJACENT
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Weakness Type (CWE)
EPSS
Base Score:
0.17