CVE-2026-76816

Netty: MQTT Topic Name and Client ID Validation Bypass

Published: Aug 24, 2026Updated: Sep 9, 2026 Sources: CVE List NVDCWE-20

3.5LOW

Description

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.

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:AAttack Vector

Adjacent

AC:LAttack Complexity

Low

PR:LPrivileges Required

Low

UI:NUser Interaction

None

Scope

S:UScope

Unchanged

Impact

C:NConfidentiality

None

I:LIntegrity

Low

A:NAvailability

None

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Weaknesses

CWE-20 CWE-626

Affected Products

netty

oss-projectaka netty-incubator-codec-ohttp, io.netty:netty

nettyLibraryLibrary

OSS Libraries / generic-library

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

1 technique

Initial Access

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References

https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7

github.com

https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961

github.com

https://github.com/netty/netty/security/advisories/GHSA-43fm-7cxg-hf3j

github.com

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