NIST deprecates RSA-2048 from 2030. Find every one of them before attackers do.
☕ Maven
Not in CISA KEV

CVE-2026-69204 — http4s-ember-core_2.12

Fix: http4s/http4s@9feaf86

CVE-2026-69204 is a CWE-444 vulnerability in org.http4s:http4s-ember-core_2.12. A fix is available for org.http4s:http4s-ember-core_2.12 — see the affected versions and patch details below.

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

Also known asGHSA-8h4c-x2wg-6xp8
Published
Updated
Affected
5 pkgs
Patched
5 / 5
Exploits
None indexed
Exploitation data as of Oct 29, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • A successful exploit gives an attacker total control of the affected component, not partial access.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-69204.

EPSS Exploitation Probability

via FIRST.org ↗
0.6%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs47th percentile — riskier than 47% of all scored CVEsHighest risk
0.07%0.41%0.74%1.07%0.6%0.6%Oct 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

5 pkgs affected
☕org.http4s:http4s-ember-core_2.12☕org.http4s:http4s-ember-core_2.13☕org.http4s:http4s-ember-core_3☕org.http4s:http4s-ember-core_2.13☕org.http4s:http4s-ember-core_3

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

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 with the next request key in a caching proxy.

Client

ember-client shares the same parser on the response path. An upstream that sends both headers can desync a pooled client connection. This requires a malicious or compromised upstream.

Preconditions

  • Unauthenticated remote attacker (server)
  • ember-server as origin behind a keep-alive intermediary
  • Intermediary forwards a request carrying both Transfer-Encoding and Content-Length (RFC says it MAY reject; many forward) and frames by Content-Length
  • Malicious or compromised upstream (client)

Workarounds

  • Intermediary strictly rejects requests carrying both Transfer-Encoding and Content-Length
  • Intermediary buffers and re-encodes request bodies
  • Disable backend keep-alive between the intermediary and Ember

Affected Packages

5 total 5 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.http4s:http4s-ember-core_2.12all versions0.23.35org.http4s:http4s-ember-core_2.12:0.23.35
☕Mavenorg.http4s:http4s-ember-core_2.13all versions0.23.35org.http4s:http4s-ember-core_2.13:0.23.35
☕Mavenorg.http4s:http4s-ember-core_3all versions0.23.35org.http4s:http4s-ember-core_3:0.23.35
☕Mavenorg.http4s:http4s-ember-core_2.13≥ 1.0.0-M1&&< 1.0.0-M471.0.0-M47org.http4s:http4s-ember-core_2.13:1.0.0-M47
☕Mavenorg.http4s:http4s-ember-core_3≥ 1.0.0-M1&&< 1.0.0-M471.0.0-M47org.http4s:http4s-ember-core_3:1.0.0-M47

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.http4s:http4s-ember-core_2.12, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.http4s:http4s-ember-core_2.12 to 0.23.35 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-69204 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

## 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 frame
O3 Security · Impact-Aware SCA

Is CVE-2026-69204 in your dependencies?

Find it across Maven, including transitive dependencies.

Scan my dependencies How O3 SCA works
CVE-2026-69204: http4s-ember-core_2 — Fixed in 0.23.35