Netty HTTP/1.0 TE+CL Coexistence Bypasses Smuggling Sanitization

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

EPSS

• CVE-2026-42581: 0.63% estimated exploitation activity in the next 30 days; percentile 50.26 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

NETTY HTTP/1.0 TE+CL Coexistence Bypasses Smuggling Sanitization | Field | Value | |-----------|-------| | Library | io.netty:netty-codec-http | | Component | codec-http — HttpObjectDecoder | | Severity | HIGH | | Affects | HEAD, commit 4f3533ae confirmed | --- Summary HttpObjectDecoder strips a conflicting Content-Length header when a request carries both Transfer-Encoding: chunked and Content-Length, but only for HTTP/1.1 messages. The guard is absent for HTTP/1.0. An attacker that sends an HTTP/1.0 request with both headers causes Netty to decode the body as chunked while leaving Content-Length intact in the forwarded HttpMessage. Any downstream proxy or handler that trusts Content-Length over Transfer-Encoding will disagree on message boundaries, enabling request smuggling. --- Root Cause The conflict-resolution path is gated on message.protocolVersion() == HttpVersion.HTTP11. When the request declares HTTP/1.0, the condition is false,…

Published by the source

7 May 2026, 00:18 UTC

Last modified by the source

14 May 2026, 20:41 UTC

Source last checked

26 Oct 2026, 16:45 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-xxqh-mfjm-7mv9

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-42581

Advisory: Netty HTTP/1.0 TE+CL Coexistence Bypasses Smuggling Sanitization
IDs: CVE-2026-42581, GHSA-xxqh-mfjm-7mv9
Record: https://patchnext.com/advisories/cve-2026-42581 (revision 1, source checked 26 Oct 2026, 16:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: io.netty:netty-codec-http 4.2.13.Final, 4.1.133.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.netty:netty-codec-http: affected >= 4.2.0.Alpha1, <= 4.2.12.Final; <= 4.1.132.Final; fixed in 4.2.13.Final, 4.1.133.Final

## Suggested inspection (read-only)
- Maven io.netty:netty-codec-http: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.netty:netty-codec-http.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-xxqh-mfjm-7mv9 (GitHub-reviewed advisory GHSA-xxqh-mfjm-7mv9 lists affected ranges: Maven io.netty:netty-codec-http >=4.2.0.Alpha1 =0 <=4.1.132.Final)

Commands are suggestions: review each one before running it.