CVE-2025-61684Network attack vector

Process crash via invalid QUIC frame handling

Published Jan 19, 2026 · Updated Jan 19, 2026

Improper input validation in H2O quicly before commit d9d3df6 allows remote attackers to crash its host process using invalid QUIC frames. Quicly's frame-processing path fails to reject certain invalid QUIC frames and instead reaches internal assertions that terminate the process. No authentication or user interaction is required; a shared process serving multiple QUIC connections drops innocent connections when it crashes.

CVSS severity7.5
High
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in H2O quicly before commit d9d3df6 allows remote attackers to crash its host process using invalid QUIC frames. Quicly's frame-processing path fails to reject certain invalid QUIC frames and instead reaches internal assertions that terminate the process. No authentication or user interaction is required; a shared process serving multiple QUIC connections drops innocent connections when it crashes.

The record

CVE
CVE-2025-61684
Published
Jan 19, 2026
Updated
Jan 19, 2026
Vendor
H2O Project
Product
quicly
Classifications
CWE-617, CWE-20, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 19, 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=< d9d3df6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

H2O Project · quiclyversion=< d9d3df6

Published CVSS scores

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
CWE-20Improper Input Validation
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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