---
title: "CVE-2026-69204: Http4s Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)"
url: https://erroneo.us/security/cve/CVE-2026-69204/
description: "CVE-2026-69204 (org.http4s:http4s-ember-core_2.12 (Maven)): Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, Ember HTTP/1.1…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-09-15
date_modified: 2026-09-15
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-69204"
kev: false
cvss: 9.2
epss: 0.00574
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-69204: Http4s Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.6% , percentile 47: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 47% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes org.http4s:http4s-ember-core_2.12 (Maven) <= 0.23.34, fixed in 0.23.35 ; org.http4s:http4s-ember-core_2.13 (Maven) <= 0.23.34, fixed in 0.23.35 ; org.http4s:http4s-ember-core_3 (Maven) <= 0.23.34, fixed in 0.23.35 ; org.http4s:http4s-ember-core_2.13 (Maven) >= 1.0.0-M1, <= 1.0.0-M46, fixed in 1.0.0-M47 . Check your lockfile, including transitive dependencies.

## What it is

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, Ember HTTP/1.1 does not reject messages containing both Transfer-Encoding and Content-Length, so an intermediary and Ember can select different body framing rules. When ember-server is behind a keep-alive intermediary that forwards both headers and frames by Content-Length, an unauthenticated attacker can smuggle a second request, bypass intermediary access controls, poison caches, or cause a victim request to be joined to an attacker-controlled prefix. The shared response parser can also desynchronize an ember-client connection when a malicious or compromised upstream sends both headers. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

## Affected packages

- Maven `org.http4s:http4s-ember-core_2.12` <= 0.23.34 → fixed: 0.23.35
- Maven `org.http4s:http4s-ember-core_2.13` <= 0.23.34 → fixed: 0.23.35
- Maven `org.http4s:http4s-ember-core_3` <= 0.23.34 → fixed: 0.23.35
- Maven `org.http4s:http4s-ember-core_2.13` >= 1.0.0-M1, <= 1.0.0-M46 → fixed: 1.0.0-M47
- Maven `org.http4s:http4s-ember-core_3` >= 1.0.0-M1, <= 1.0.0-M46 → fixed: 1.0.0-M47

## Affected products (CVE record)

- http4s http4s: < 0.23.35, >= 1.0.0-M1, < 1.0.0-M47

## Severity

- GitHub_M 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`
- GitHub 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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.57% probability of exploitation activity in the next 30 days; percentile 47.

## Sources

- [GitHub Advisory GHSA-8h4c-x2wg-6xp8](https://github.com/advisories/GHSA-8h4c-x2wg-6xp8)
- [CVE.org record CVE-2026-69204](https://www.cve.org/CVERecord?id=CVE-2026-69204)
- [NVD entry CVE-2026-69204](https://nvd.nist.gov/vuln/detail/CVE-2026-69204)
- [github.com](https://github.com/http4s/http4s/security/advisories/GHSA-8h4c-x2wg-6xp8)
- [github.com](https://github.com/http4s/http4s/commit/9feaf8677951a52af906ae9664ff6f0543d9d810)
- [github.com](https://github.com/http4s/http4s/releases/tag/v0.23.35)
- [github.com](https://github.com/http4s/http4s/releases/tag/v1.0.0-M47)

---
Source page: https://erroneo.us/security/cve/CVE-2026-69204/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt