Log in Start free

Vulnerability · Published Sep 15, 2026 · Assigned by GitHub_M

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

Critical 9.2

In plain English

A critical-severity security flaw in http4s from http4s. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 48% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)9.2Critical
Exploit odds (30 days)0.6%top 52.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 & fixed versions

EcosystemPackageFixed inAdvisory
Mavenorg.http4s:http4s-ember-core_2.120.23.35GHSA-8h4c-x2wg-6xp8
Mavenorg.http4s:http4s-ember-core_2.130.23.35GHSA-8h4c-x2wg-6xp8
Mavenorg.http4s:http4s-ember-core_2.131.0.0-M47GHSA-8h4c-x2wg-6xp8
Mavenorg.http4s:http4s-ember-core_30.23.35GHSA-8h4c-x2wg-6xp8
Mavenorg.http4s:http4s-ember-core_31.0.0-M47GHSA-8h4c-x2wg-6xp8

Affected products (as reported)

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

Weakness: CWE-444 · Vector: 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

References