High 7.5Published Sep 15, 2026

CVE-2026-69209Http4s: WebSocket decoder accepts unbounded message sizes

Updated under an hour ago (2026-10-19 08:50 UTC)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, The shared WebSocket decoder permits unbounded message buffering because defragmentation accumulates fragments without a limit and FrameTranscoder accepts declared lengths up to Int.MaxValue. A remote client that completes a WebSocket handshake against an http4s-blaze-server or http4s-ember-server endpoint can exhaust server memory with oversized frames or fragmented messages. The patched decoder applies a configurable 64 MiB default limit to individual frames and defragmented messages through EmberServerBuilder.withMaxWebSocketMessageSize. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-400, CWE-770
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Sep 16, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

http4s http4s http4s:http4s (from the name)	before 0.23.35; from 1.0.0-M1, < 1.0.0-M47	CNA record

References

https://github.com/http4s/http4s/security/advisories/GHSA-jrxx-w2m8-5hf5x-refsource-confirm
https://github.com/http4s/http4s/commit/d578c3c9da6193627d40fa785e612cda7fcd77b3x-refsource-misc
https://github.com/http4s/http4s/releases/tag/v0.23.35x-refsource-misc
https://github.com/http4s/http4s/releases/tag/v1.0.0-M47x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.