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CVE-2026-69209

Http4s: WebSocket decoder accepts unbounded message sizes

High7.5EPSS 0.63%
Published
Updated
Reserved
Assigned by
GitHub_M

Description

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.

Scores

CVSS scores of CVE-2026-69209, by who scored it
Scored byCVSSScoreVector
GitHub_MCNA (assigner)3.1High7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVDNVD · Deferred3.1High7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS (exploitation in 30 days)
0.63% · top 50% of all CVEs (6 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: yes · Technical impact: partial
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The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.

Weakness

Affected products

  • http4s · http4s

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

References (4)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .