What’s Vulnerable › Vulnerabilities

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

• Severity: critical (CVSS 9.2 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-15 · updated 2026-09-16
• Weakness: CWE-444

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 products

• http4s: before 0.23.35; from 1.0.0-M1, < 1.0.0-M47

References

• https://github.com/http4s/http4s/commit/9feaf8677951a52af906ae9664ff6f0543d9d810
• https://github.com/http4s/http4s/releases/tag/v0.23.35
• https://github.com/http4s/http4s/releases/tag/v1.0.0-M47
• https://github.com/http4s/http4s/security/advisories/GHSA-8h4c-x2wg-6xp8

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