Is CVE-2026-69210 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-69210 being exploited in the wild.

How severe is CVE-2026-69210?

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

Which products and versions are affected?

Http4s before 0.23.35 and before 1.0.0-M47.

Is there a fix for CVE-2026-69210?

A patch was published on 2026-07-06: v0.23.35 released on July 6, 2026 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-69210 attacked?

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

Am I affected by CVE-2026-69210?

Check whether you run Http4s 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-2026-69210: Http4s WebSocket decoder negative length handling denial of service

CVE-2026-69210 · Severity: high · CVSS 7.5 · Published 2026-09-15

Http4s is a Scala HTTP framework used to build web services with WebSocket support. The WebSocket frame decoder contains a vulnerability that allows remote clients to trigger an infinite decode loop by sending frames with negative payload lengths. An attacker can exploit this to cause complete CPU exhaustion and unbounded memory growth on affected servers, resulting in service unavailability.

Technologies: Http4s. Vendors: Http4s.

Quick answers

Is CVE-2026-69210 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-69210 being exploited in the wild.
How severe is CVE-2026-69210?: High severity, with a CVSS score of 7.5, published 15 September 2026.
Which products and versions are affected?: Http4s before 0.23.35 and before 1.0.0-M47.
Is there a fix for CVE-2026-69210?: A patch was published on 2026-07-06: v0.23.35 released on July 6, 2026 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-69210 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-69210?: Check whether you run Http4s 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 WebSocket FrameTranscoder.bodyLength component in Http4s prior to versions 0.23.35 and 1.0.0-M47 incorrectly validates payload length fields in WebSocket frames. While it rejects lengths above Integer.MAX_VALUE, it fails to reject negative 64-bit length values. A remote client that completes a WebSocket handshake can send a specially crafted frame with a negative payload length, causing the decoder to return an empty frame without advancing the input buffer. This causes the decode loop to repeat indefinitely with the same malformed frame, consuming CPU at 100% and growing the internal ArrayBuffer without bound. The fix, available in versions 0.23.35 and 1.0.0-M47, adds proper validation to reject negative payload lengths.

Affected products

Http4s Http4s before 0.23.35 and before 1.0.0-M47

Timeline

2026-09-15: disclosed
2026-07-06: patched: v0.23.35 released on July 6, 2026

References

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