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

Source: https://junglewise.ai/threats/cve-2026-42585-netty-http-request-smuggling-via-malformed-transfer-encoding  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-05-15  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-http), [Netty Project Netty codec-http](https://junglewise.ai/threats/technologies/codec-http). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty Project](https://junglewise.ai/threats/vendors/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

  ```sh
  # 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](https://github.com/netty/netty/security/advisories/GHSA-38f8-5428-x5cv)

## Related threats

- [Netty HttpServerCodec response desynchronization](https://junglewise.ai/threats/cve-2026-100666-netty-s-httpservercodec-io-netty-netty-codec-http-in-versions-4)
- [Netty CorsHandler cache poisoning via Vary header overwrite](https://junglewise.ai/threats/cve-2026-59903-netty-corshandler-cache-poisoning-via-vary-header-overwrite)
- [Netty HTTP request smuggling via lax WebSocket handshake validation](https://junglewise.ai/threats/cve-2026-59898-netty-http-request-smuggling-via-lax-websocket-handshake)
- [Netty resource exhaustion in HttpContentEncoder via HTTP pipelining](https://junglewise.ai/threats/cve-2026-59899-netty-resource-exhaustion-in-httpcontentencoder-via-http)
- [Netty CRLF injection in HttpPostRequestEncoder multipart filenames](https://junglewise.ai/threats/cve-2026-59921-netty-crlf-injection-in-httppostrequestencoder-multipart)