CVE-2026-42581: Netty

Critical severity, CVSS 9.8. EPSS: 0.7% chance of exploitation in the next 30 days.

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpObjectDecoder strips a conflicting Content-Length header when a request carries both Transfer-Encoding: chunked and Content-Length, but only for HTTP/1.1 messages. The guard is absent for HTTP/1.0. An attacker that sends an HTTP/1.0 request with both headers causes Netty to decode the body as chunked while leaving Content-Length intact in the forwarded HttpMessage. Any downstream proxy or handler that trusts Content-Length over Transfer-Encoding will disagree on message boundaries, enabling request smuggling. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Affected products

• Netty Netty: before 4.1.133 (fixed in 4.1.133); from 4.2.0, before 4.2.13 (fixed in 4.2.13)

Published 2026-05-13. Last modified 2026-09-18.