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Http4s: WebSocket decoder accepts unbounded message sizes

CVSS 3.1 7.5 HIGHCheck source for fixed versionsKEV status unknown

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.

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CVE-2026-69209 · CVE overview and exploitation status

cve-program · CVE-2026-69209

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Sources read 13 Nov 09:00 UTC · 274 of 275 readable · 272 fully read · documentation 469/469 current