CVE-2026-69202 Http4s Ember HTTP/2: unbounded inbound body buffering

What is CVE-2026-69202?

CVE-2026-69202 is a high-severity denial of service 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/2 flow-control window is replenished according to bytes received from the network rather than bytes consumed by the application, while each stream stores DATA in an unbounded channel. A hostile peer can therefore send a body faster than a slow or non-draining application consumes it, retaining payloads in heap on an ember-server or ember-client configured with withHttp2. The patch bounds the per-stream H2Connection body channel so application consumption applies backpressure. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

Weakness: CWE-770, CWE-400

Which versions are affected by CVE-2026-69202?

10 open source packages ship an affected version, including org.http4s:http4s-ember-core_2.13, org.http4s:http4s-ember-core_2.12 and org.http4s:http4s-ember-core_3.

How do I fix CVE-2026-69202?

Upgrade org.http4s:http4s-ember-core_2.13 to a fixed version for your release line: 0.23.35 or 1.0.0-M47.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-69202 being exploited?

There is no known exploitation of CVE-2026-69202 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-6m4x-pp6q-5jmm.