CVE-2026-69217 Http4s: Ember Server accepts duplicate Content-Length headers
Attackers can exploit HTTP request smuggling in Http4s Ember server to bypass controls, capture user headers, or poison caches.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-69217?
CVE-2026-69217 is a high-severity vulnerability in http4s, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, Ember’s HTTP/1.1 parser accepts differing duplicate Content-Length headers and uses the last value instead of rejecting the message. When an Ember server is behind a keep-alive intermediary that selects a different occurrence, an unauthenticated attacker can create CL.CL request smuggling that bypasses front-end controls, captures a later user’s headers, or poisons a cache. The shared client parser can also misframe responses from a malicious or compromised upstream when the client acts as a proxy for multiple downstream consumers. This issue is fixed in versions 0.23.35 and 1.0.0-M47.
Weakness: CWE-444
Which versions are affected by CVE-2026-69217?
How do I fix CVE-2026-69217?
No fix has been published for CVE-2026-69217 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-69217 being exploited?
There is no known exploitation of CVE-2026-69217 in the wild and no public exploit code.
Sources
Also known as GHSA-p83c-4wj9-p6w9.