Low severity · published Aug 24, 2026
CVE-2026-76816
Netty: MQTT Topic Name and Client ID Validation Bypass
3.5
CVSS
0.2%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Attack vector
Adjacent
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 7% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NE
netty · netty
>= 4.2.0.Final, < 4.1.137.Final; < 4.1.137.Final · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-76816
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-76816
github.com
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
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