Is CVE-2026-69209 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-69209 being exploited in the wild.

How severe is CVE-2026-69209?

High severity, with a CVSS score of 7.5, published 15 September 2026.

Which products and versions are affected?

Http4s-Blaze-Server prior to 0.23.35; Http4s-Ember-Server prior to 0.23.35 and prior to 1.0.0-M47.

Is there a fix for CVE-2026-69209?

A patch was published on 2026-06-29: Fix committed to http4s repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-69209 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-69209?

Check whether you run Http4s-Blaze-Server or Http4s-Ember-Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-69209: http4s WebSocket decoder unbounded message buffering

CVE-2026-69209 · Severity: high · CVSS 7.5 · Published 2026-09-15

http4s is a Scala web services framework that handles WebSocket connections. A flaw in its WebSocket decoder allows remote clients to exhaust server memory by sending oversized or fragmented messages without limits, causing service outages. This affects http4s-blaze-server and http4s-ember-server deployments exposed to untrusted network clients.

Vendors: Http4s.

Quick answers

Is CVE-2026-69209 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-69209 being exploited in the wild.
How severe is CVE-2026-69209?: High severity, with a CVSS score of 7.5, published 15 September 2026.
Which products and versions are affected?: Http4s-Blaze-Server prior to 0.23.35; Http4s-Ember-Server prior to 0.23.35 and prior to 1.0.0-M47.
Is there a fix for CVE-2026-69209?: A patch was published on 2026-06-29: Fix committed to http4s repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-69209 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-69209?: Check whether you run Http4s-Blaze-Server or Http4s-Ember-Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is an unbounded resource consumption flaw in the WebSocket frame decoder. The root cause is twofold: the defragmentation logic accumulates message fragments without enforcing a size limit, and the FrameTranscoder accepts declared frame lengths up to Int.MaxValue. A remote attacker who completes a WebSocket handshake can send oversized frames or fragmented messages to trigger uncontrolled memory buffering. No authentication is required; the attack is triggered via network access to a WebSocket endpoint. The fix applies a configurable 64 MiB default limit per frame and defragmented message through EmberServerBuilder.withMaxWebSocketMessageSize, available in versions 0.23.35 and 1.0.0-M47.

Affected products

http4s http4s-blaze-server prior to 0.23.35
http4s http4s-ember-server prior to 0.23.35 and prior to 1.0.0-M47

Timeline

2026-09-15: disclosed: Public disclosure via NVD
2026-06-29: patched: Fix committed to http4s repository
2026-07-06: patched: Released in v0.23.35

References

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