CVE-2026-69204

CVE-2026-69204 is a critical-severity vulnerability with a CVSS 4.0 base score of 9.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-444.

Key facts

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.

Frequently asked questions

What is CVE-2026-69204?
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.
How severe is CVE-2026-69204?
CVE-2026-69204 has a CVSS 4.0 base score of 9.2, rated critical severity.
Is CVE-2026-69204 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (46th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-69204?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2026-69204 published?
CVE-2026-69204 was published on 2026-09-15 and last updated on 2026-09-16.

References

Other CWE-444 (HTTP Request/Response Smuggling) vulnerabilities

Browse all CWE-444 (HTTP Request/Response Smuggling) vulnerabilities →