CVE-2026-69210Network attack vectorHinoki check available

Server hang via negative WebSocket frame length

Published Sep 15, 2026 · Updated Sep 15, 2026

Denial of service in http4s before 0.23.35 allows remote attackers to hang Ember servers via a crafted WebSocket frame. After a WebSocket handshake, FrameTranscoder.bodyLength accepts a negative 64-bit extended payload length, so decoding returns an empty frame without consuming input. The stalled loop pins a worker at full CPU and grows an ArrayBuffer without bound; 1.0.0-M1 through 1.0.0-M46 is also affected.

CVSS severityUnavailable
Unscored
EPSS probability0.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Denial of service in http4s before 0.23.35 allows remote attackers to hang Ember servers via a crafted WebSocket frame. After a WebSocket handshake, FrameTranscoder.bodyLength accepts a negative 64-bit extended payload length, so decoding returns an empty frame without consuming input. The stalled loop pins a worker at full CPU and grows an ArrayBuffer without bound; 1.0.0-M1 through 1.0.0-M46 is also affected.

The record

CVE
CVE-2026-69210
Published
Sep 15, 2026
Updated
Sep 15, 2026
Vendor
http4s
Product
http4s
Classifications
T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 15, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.23.35
  2. Affected versionversion=>= 1.0.0-M1, < 1.0.0-M47

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

http4s · http4sversion=< 0.23.35; version=>= 1.0.0-M1, < 1.0.0-M47

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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