Http4s Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)

Exploitation

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

CVSS 4.0

9.2 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-69204: 0.57% estimated exploitation activity in the next 30 days; percentile 47.46 (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 Ember's HTTP/1.1 request parser does not reject a message that carries both a Transfer-Encoding and a Content-Length header. RFC 9112 §6.1 requires a server to treat such a message as a framing error and close the connection. An intermediary that follows the RFC's CL-strip-and-forward path (or that prioritises Content-Length) will frame the body differently from Ember, enabling HTTP request smuggling (CL.TE). Impact Server Request smuggling when ember-server is an origin behind an intermediary that forwards both headers over a keep-alive backend connection and frames by Content-Length while Ember frames by chunked: - Front-end security bypass: the smuggled request reaches paths the intermediary's ACL/auth layer would have blocked, with attacker-chosen method and headers. - Cross-user request hijack: a dangling smuggled prefix concatenates with the next victim's request on the shared backend socket, capturing its headers. - Cache poisoning: the smuggled response is associated…

Published by the source

15 Sep 2026, 19:53 UTC

Last modified by the source

15 Sep 2026, 20:00 UTC

Source last checked

26 Oct 2026, 16:55 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-8h4c-x2wg-6xp8

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-8h4c-x2wg-6xp8

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# Patch Next advisory brief: CVE-2026-69204

Advisory: Http4s Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)
IDs: CVE-2026-69204, GHSA-8h4c-x2wg-6xp8
Record: https://patchnext.com/advisories/cve-2026-69204 (revision 3, source checked 26 Oct 2026, 16:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.http4s:http4s-ember-core_2.12 0.23.35; org.http4s:http4s-ember-core_3 1.0.0-M47, 0.23.35; org.http4s:http4s-ember-core_2.13 1.0.0-M47, 0.23.35. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.http4s:http4s-ember-core_2.12: affected <= 0.23.34; fixed in 0.23.35
- Maven org.http4s:http4s-ember-core_3: affected <= 0.23.34; >= 1.0.0-M1, <= 1.0.0-M46; fixed in 0.23.35, 1.0.0-M47
- Maven org.http4s:http4s-ember-core_2.13: affected <= 0.23.34; >= 1.0.0-M1, <= 1.0.0-M46; fixed in 0.23.35, 1.0.0-M47

## Suggested inspection (read-only)
- Maven org.http4s:http4s-ember-core_2.12: check the installed version with your package manager.
- Maven org.http4s:http4s-ember-core_3: check the installed version with your package manager.
- Maven org.http4s:http4s-ember-core_2.13: 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 org.http4s:http4s-ember-core_2.12, org.http4s:http4s-ember-core_3, org.http4s:http4s-ember-core_2.13.
- 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://osv.dev/vulnerability/GHSA-8h4c-x2wg-6xp8 (OSV record GHSA-8h4c-x2wg-6xp8 lists affected ranges: Maven org.http4s:http4s-ember-core_2.12 >=0 =0 =1.0.0-M1 =0 =1.0.0-M1 <1.0.0-M47 (fixed))
- Verified: https://github.com/advisories/GHSA-8h4c-x2wg-6xp8 (GitHub-reviewed advisory GHSA-8h4c-x2wg-6xp8 lists affected ranges: Maven org.http4s:http4s-ember-core_2.12 >=0 =0 =1.0.0-M1 =0 =1.0.0-M1 <=1.0.0-M46)

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