Netty vulnerable to HTTP Request Smuggling due to malformed Transfer-Encoding

Exploitation

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

CVSS

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

EPSS

• CVE-2026-42585: 0.27% estimated exploitation activity in the next 30 days; percentile 18.88 (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.

Summary Netty incorrectly parses malformed Transfer-Encoding, enabling request smuggling attacks. Details Netty incorrectly marks a request as chunked when malformed "Transfer-Encoding: chunked, identity" is present. According to RFC https://datatracker.ietf.org/doc/html/rfc9112#name-message-body-length " If a Transfer-Encoding header field is present in a request and the chunked transfer coding is not the final encoding, the message body length cannot be determined reliably; the server MUST respond with the 400 (Bad Request) status code and then close the connection. " A possible scenario is when Netty is behind a proxy that doesn't reject requests with "Transfer-Encoding: chunked, identity", but prefers "Content-Length" and forwards the content to Netty. PoC The test below shows Netty successfully parsing the second request, demonstrating how an attacker can smuggle a second request inside a request body. Impact HTTP Request Smuggling: Attacker injects arbitrary HTTP requests

Published by the source

7 May 2026, 00:22 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-38f8-5428-x5cv

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# Patch Next advisory brief: CVE-2026-42585

Advisory: Netty vulnerable to HTTP Request Smuggling due to malformed Transfer-Encoding
IDs: CVE-2026-42585, GHSA-38f8-5428-x5cv
Record: https://patchnext.com/advisories/cve-2026-42585 (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 6.5)
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-38f8-5428-x5cv (GitHub-reviewed advisory GHSA-38f8-5428-x5cv lists affected ranges: Maven io.netty:netty-codec-http >=4.2.0.Alpha1 =0 <=4.1.132.Final)

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