Is CVE-2026-42578 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-42578 being exploited in the wild.

How severe is CVE-2026-42578?

High severity, with a CVSS score of 7.5, published 13 May 2026.

Which products and versions are affected?

io.netty:netty-handler-proxy (Maven) ECOSYSTEM:introduced=0,fixed=4.1.133.Final.

Is there a fix for CVE-2026-42578?

Yes. io.netty:netty-handler-proxy (Maven): upgrade to 4.1.133.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-42578 attacked?

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

Am I affected by CVE-2026-42578?

Check whether you run io.netty:netty-handler-proxy (Maven) or Netty Project Handler Proxy 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-2026-42578: Netty HTTP header injection in HttpProxyHandler

CVE-2026-42578 · Severity: high · CVSS 7.5 · Published 2026-05-13

Netty is a widely used networking framework that helps developers build high-performance web applications and services. A security flaw in its proxy handling component allows attackers to inject malicious data into the communication headers sent to a proxy server. This could be used to bypass security controls, spoof identity, or perform request smuggling attacks, potentially compromising the integrity of the connection between the application and its proxy.

Vendors: Maven, Netty Project.

Quick answers

Is CVE-2026-42578 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-42578 being exploited in the wild.
How severe is CVE-2026-42578?: High severity, with a CVSS score of 7.5, published 13 May 2026.
Which products and versions are affected?: io.netty:netty-handler-proxy (Maven) ECOSYSTEM:introduced=0,fixed=4.1.133.Final.
Is there a fix for CVE-2026-42578?: Yes. io.netty:netty-handler-proxy (Maven): upgrade to 4.1.133.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42578 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-42578?: Check whether you run io.netty:netty-handler-proxy (Maven) or Netty Project Handler Proxy 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-handler-proxy (Maven): upgrade to 4.1.133.Final or later

# set io.netty:netty-handler-proxy to 4.1.133.Final in your pom.xml or build.gradle

Technical details

A vulnerability exists in Netty's HttpProxyHandler where the newInitialMessage() method explicitly disables header validation by using DefaultHttpHeadersFactory.headersFactory().withValidation(false). When user-provided outboundHeaders are added to the CONNECT request, the lack of CRLF validation allows an attacker who can influence these headers to inject arbitrary HTTP headers. This is an incomplete fix for a previous vulnerability (GHSA-84h7-rjj3-6jx4). Attackers can leverage this to bypass proxy authentication or perform request smuggling. The issue is resolved in versions 4.2.13.Final and 4.1.133.Final by ensuring proper validation is applied to these header fields.

Affected products

Netty Project Netty < 4.2.13.Final, < 4.1.133.Final

Identifiers

CVE-2026-42578
GHSA-45q3-82m4-75jr

Timeline

2026-05-05: advisory: GitHub Security Advisory published
2026-05-13: disclosed: NVD publication date

References

https://github.com/netty/netty/security/advisories/GHSA-45q3-82m4-75jr

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