CVE-2026-76816: netty Improper Input Validation

Vulnerability summary

CVE-2026-76816 is a low (CVSS 3.5) Improper Input Validation vulnerability in netty. EPSS estimates a 0.17% chance of exploitation in the next 30 days, higher than 6.4% of scored vulnerabilities.

Timeline

1. 24-08-2026
   PublishedVulnerability first disclosed.
2. 25-08-2026
   Last modifiedVulnerability information updated.

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.

• CWE-20Improper Input ValidationThe product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
• CWE-626Null Byte Interaction Error (Poison Null Byte)The product does not properly handle null bytes or NUL characters when passing data between different representations or components.