Improper input validation in Netty

CVE-2026-76816

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.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 3.5 (Low). Vector: CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (6.3th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 6th percentile — 6.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-76816: held from 0.002 to 0.002.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000

Affected products

  • Netty — versions < 4.1.137.Final, >= 4.2.0.Final, < 4.1.137.Final

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-76816?
CVE-2026-76816 is a low-severity vulnerability in Netty, classified under Improper Input Validation. CVSS score: 3.5/10. Published 2026-08-24.
How severe is CVE-2026-76816?
Low severity. CVSS v3 base score is 3.5 out of 10.