CVE-2026-69209

HIGH 7.5

Http4s: WebSocket decoder accepts unbounded message sizes

CVSS Score

7.5

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-400 CWE-770
Vendor	http4s
Product	http4s
Published	Sep 15, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Affected Versions

http4s / http4s

< 0.23.35 >= 1.0.0-M1, < 1.0.0-M47

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/http4s/http4s/security/advisories/GHSA-jrxx-w2m8-5hf5 github.com: https://github.com/http4s/http4s/commit/d578c3c9da6193627d40fa785e612cda7fcd77b3 github.com: https://github.com/http4s/http4s/releases/tag/v0.23.35 github.com: https://github.com/http4s/http4s/releases/tag/v1.0.0-M47