CVE-2026-42580: Netty integer overflow in HTTP chunk size parser

CVE-2026-42580 · 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 flaw in how it handles large data transfers allows an attacker to hide a second, unauthorized request inside a legitimate one. This can lead to 'request smuggling,' where an attacker bypasses security controls to perform unauthorized actions or interfere with other users' sessions.

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

Quick answers

Is CVE-2026-42580 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42580 being exploited in the wild.
How severe is CVE-2026-42580?
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-2026-42580?
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-2026-42580 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-42580?
Check whether you run io.netty:netty-codec-http (Maven) 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 integer overflow vulnerability exists in Netty's HTTP chunk size parser within the HttpObjectDecoder component. When processing chunked transfer encoding, the parser accumulates the chunk size using a 32-bit integer without sufficient overflow checks; specifically, it only checks if the final result is negative. By providing a carefully crafted hex chunk size (e.g., 100000004), an attacker can cause the parser to miscalculate the remaining data length. This allows a malicious actor to 'smuggle' a second HTTP request within the body of the first, which may be interpreted as a separate request by downstream servers or proxies. The issue is resolved in Netty 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-2026-42580
  • GHSA-m4cv-j2px-7723

Timeline

  • 2026-05-05: advisory: GitHub Security Advisory published
  • 2026-05-13: disclosed: CVE published to NVD

References

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