Public mode

No access to your tenant or devices. Every item links to its source. What this means

CVE-2026-69209

Http4s: WebSocket decoder accepts unbounded message sizes

CVSS 3.1 7.5 HIGHCheck source for fixed versionsKEV status unknown

Original advisory

cve-program · CVE-2026-69209

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-69209

Published

http4s

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "http4s",
                    "product": "http4s",
                    "versions": [
                        {
                            "version": "< 0.23.35",
                            "status": "affected"
                        },
                        {
                            "version": ">= 1.0.0-M1, < 1.0.0-M47",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON