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Fencer Vulns
low 3.5

CVE-2026-76816 json

Netty: MQTT Topic Name and Client ID Validation Bypass

published 2026-08-24 2 mo ago modified 2026-10-12 27 d ago also EUVD-2026-65093

cvss
3.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 6%
public exploits
0
none known

Summary

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.

Patch / fix

  • netty-tcnative SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 2.0.84-150200.3.51.1
  • netty SLE Module for Package Hub 15 SP7 4.1.138-150200.4.56.1

suse advisories SUSE-SU-2026:4391-1

  • netty openSUSE Tumbleweed 4.1.138-1.1

opensuse advisories openSUSE-SU-2026:11882-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-76816 updated cvss 3.5

io.netty/netty-codec-mqtt: Netty: MQTT validation bypass leading to message integrity issues

  • Red Hat AMQ Broker 7 netty-codec-mqtt 4.1.137.Final-redhat-00001 Red Hat build of Apache Camel for Spring Boot 4 netty-codec-mqtt 4.1.137.Final-redhat-00001
    affected: no fix available “Fix deferred”
  • Red Hat Fuse 7 netty-codec-mqtt 4.1.137.Final-redhat-00001 Red Hat JBoss Enterprise Application Platform 7 netty-codec-mqtt 4.1.137.Final-redhat-00001, jboss-eap-7/eap74-els-openjdk8-openshift-rhel8, jboss-eap-7/eap74-els-openjdk11-openshift-rhel8, jboss-eap-7/eap74-els-openjdk17-openshift-rhel8 Red Hat Single Sign-On 7 netty-codec-mqtt 4.1.137.Final-redhat-00001
    affected: no fix planned “Out of support scope”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.5 CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Affected products

  • netty netty

Classification

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

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.