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Vulnerability record · CVE-2025-61684 · published 19 January 2026

CVE-2025-61684: H2o quicly improper input validation vulnerability

H2o · Quicly

Quicly, an IETF QUIC protocol implementation, is susceptible to a denial-of-service attack prior to commit d9d3df6a8530a102b57d840e39b0311ce5c9e14e. A remote attacker can exploit these bugs to trigger an assertion failure that crashes process using Quicly. Commit d9d3df6a8530a102b57d840e39b0311ce5c9e14e fixes the issue.

7.5 CVSS 3.1 High EPSS 0.39% · top 70.0% CWE-20 · Improper input validationCWE-617 · CWE-617
7.5CVSS 3.1 base score
0.39%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

Description

Quicly, an IETF QUIC protocol implementation, is susceptible to a denial-of-service attack prior to commit d9d3df6a8530a102b57d840e39b0311ce5c9e14e. A remote attacker can exploit these bugs to trigger an assertion failure that crashes process using Quicly. Commit d9d3df6a8530a102b57d840e39b0311ce5c9e14e fixes the issue.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/h2o/quicly/commit/d9d3df6a8530a102b57d840e39b0311ce5c9e14e Patch
https://github.com/h2o/quicly/security/advisories/GHSA-wr3c-345m-43v9 Vendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2025-61684), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.