CVE-2026-76816

MQTT routing bypass via unvalidated UTF-8 fields

Published Aug 24, 2026 · Updated Aug 25, 2026

Improper input validation in Netty before 4.1.137.Final and 4.2.0.Final through 4.2.16.Final allows remote authenticated users to alter MQTT routing. MqttEncoder length-prefixes untrusted client identifiers, usernames, will topics, and PUBLISH topics without rejecting NUL bytes or topic wildcards. Exploitation requires an application to encode user-controlled fields, after which broker interpretation differences can redirect messages or collide client identities.

CVSS severity3.5
Low
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Netty before 4.1.137.Final and 4.2.0.Final through 4.2.16.Final allows remote authenticated users to alter MQTT routing. MqttEncoder length-prefixes untrusted client identifiers, usernames, will topics, and PUBLISH topics without rejecting NUL bytes or topic wildcards. Exploitation requires an application to encode user-controlled fields, after which broker interpretation differences can redirect messages or collide client identities.

The record

CVE
CVE-2026-76816
Published
Aug 24, 2026
Updated
Aug 25, 2026
Vendor
The Netty Project
Product
Netty
Classifications
CWE-626, CWE-20
Attack vector
adjacent
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.1.137.Final
  2. Affected versionversion=>= 4.2.0.Final, < 4.1.137.Final

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesauthenticated

What is affected?

The Netty Project · Nettyversion=< 4.1.137.Final; version=>= 4.2.0.Final, < 4.1.137.Final

Published CVSS scores

8.1The Netty Project advisory narrativeCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
3.5GitHub Advisory DatabaseCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-626Null Byte Interaction Error (Poison Null Byte)
CWE-20Improper Input Validation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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