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Vulnerability record · CVE-2026-69204 · published 15 September 2026

CVE-2026-69204: HTTP request smuggling vulnerability

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.

9.2 CVSS 4.0 Critical EPSS 0.57% · top 54.8% CWE-444 · HTTP request smuggling Deferred
9.2CVSS 4.0 base score
0.57%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
16 Sep 2026Last modified by NVD

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
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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Source: NIST National Vulnerability Database (record CVE-2026-69204), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.