Is CVE-2026-42585 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-42585 being exploited in the wild.

How severe is CVE-2026-42585?

Medium severity, with a CVSS score of 6.5, published 13 May 2026.

Which products and versions are affected?

io.netty:netty-codec-http (Maven) ECOSYSTEM:introduced=4.2.0.Alpha1,fixed=4.2.13.Final.

Is there a fix for CVE-2026-42585?

Yes. io.netty:netty-codec-http (Maven): upgrade to 4.2.13.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-42585 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-42585?

Check whether you run io.netty:netty-codec-http (Maven) or Netty Project Netty codec-http at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-42585: Netty HTTP request smuggling via malformed Transfer-Encoding

CVE-2026-42585 · Severity: medium · CVSS 6.5 · Published 2026-05-13

Netty is a widely used networking framework that helps Java applications communicate over the internet. A vulnerability in how it handles web requests allows an attacker to 'smuggle' hidden commands inside a legitimate-looking request. This can lead to unauthorized access to data or the ability to bypass security controls when the application is used behind a proxy server.

Technologies: io.netty:netty-codec-http (Maven), Netty Project Netty codec-http. Vendors: Maven, Netty Project.

Quick answers

Is CVE-2026-42585 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-42585 being exploited in the wild.
How severe is CVE-2026-42585?: Medium severity, with a CVSS score of 6.5, published 13 May 2026.
Which products and versions are affected?: io.netty:netty-codec-http (Maven) ECOSYSTEM:introduced=4.2.0.Alpha1,fixed=4.2.13.Final.
Is there a fix for CVE-2026-42585?: Yes. io.netty:netty-codec-http (Maven): upgrade to 4.2.13.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42585 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-42585?: Check whether you run io.netty:netty-codec-http (Maven) or Netty Project Netty codec-http at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

io.netty:netty-codec-http (Maven): upgrade to 4.2.13.Final or later

# set io.netty:netty-codec-http to 4.2.13.Final in your pom.xml or build.gradle

Technical details

An HTTP Request Smuggling vulnerability exists in Netty's HTTP codec due to improper validation of the Transfer-Encoding header. Specifically, Netty incorrectly treats a request as chunked even when 'chunked' is not the final encoding (e.g., 'Transfer-Encoding: chunked, identity'), violating RFC 9112. If a front-end proxy ignores this malformed header and relies on Content-Length instead, an attacker can embed a second, 'smuggled' request within the body of the first. This allows for bypass of security filters or unauthorized access to other users' sessions. The issue is resolved in versions 4.2.13.Final and 4.1.133.Final.

Affected products

Netty netty-codec-http <= 4.2.12.Final, <= 4.1.132.Final

Identifiers

CVE-2026-42585
GHSA-38f8-5428-x5cv

Timeline

2026-05-05: advisory: GitHub Security Advisory published by maintainers
2026-05-13: disclosed: CVE published to NVD
2026-05-13: patched: Fixes released in versions 4.2.13.Final and 4.1.133.Final

References

https://github.com/netty/netty/security/advisories/GHSA-38f8-5428-x5cv

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.