High 7.5Published Jul 16, 2026

CVE-2026-44435Quicly: Remote Denial of Service via assertion failure when CRYPTO stream handshake data exceeds 32KB

Updated under an hour ago (Oct 27, 2026, 3:00 PM ET)

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It affects h2o quicly. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for h2o quicly

Exploited in the last 30 days

Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 937d0e9, an assertion failure is raised when the total number of valid handshake messages received over a CRYPTO stream of a single packet number space exceeds 32KB, causing a Denial of Service. This issue has been fixed by commit 937d0e9.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-617, CWE-400
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Jul 17, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

h2o quicly h2o:quicly (from the name)	before 937d0e9	CNA record
h2o quicly h2o:quicly	before 2026-05-29	NVD

References

References

https://github.com/h2o/quicly/security/advisories/GHSA-2cw9-5673-73gv	x-refsource-confirm, vendor-advisory
https://github.com/h2o/quicly/commit/937d0e9e7c669fc2bee4920632ab6aaac60e4d81	x-refsource-misc, patch

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.