CVE-2026-42581

Description

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.

How to fix CVE-2026-42581

To remediate CVE-2026-42581, upgrade the affected package to a fixed version below.

• —no fix listed
• —upgrade to 4.2.13.Final or later

Is CVE-2026-42581 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (2)

• from 0
• >= 4.2.0.Alpha1, < 4.2.13.Final

CVSS scores

References (4)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-42581
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-42581
• PATCHgithub.com/netty/netty
• WEBgithub.com/netty/netty/security/advisories/GHSA-xxqh-mfjm-7mv9