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

Source: https://junglewise.ai/threats/cve-2026-42580-netty-integer-overflow-in-http-chunk-size-parser  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-05-18  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-http). Vendors: [Maven](https://junglewise.ai/threats/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

  ```sh
  # 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

- [https://github.com/netty/netty/security/advisories/GHSA-m4cv-j2px-7723](https://github.com/netty/netty/security/advisories/GHSA-m4cv-j2px-7723)

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