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

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Summary

CVECVE-2026-44435
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-16 23:16:17 UTC
Updated2026-07-17 18:34:36 UTC
DescriptionQuicly 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

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

EPSS: 0.002780000 probability, percentile 0.198350000 (date 2026-07-17)

Problem Types: CWE-400 | CWE-617 | CWE-617 CWE-617: Reachable Assertion | CWE-400 CWE-400: Uncontrolled Resource Consumption

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA H2o Quicly affected < 937d0e9 Not specified

References

ReferenceSourceLinkTags
github.com/h2o/quicly/security/advisories/GHSA-2cw9-5673-73gv [email protected] github.com
github.com/h2o/quicly/commit/937d0e9e7c669fc2bee4920632ab6aaac60e4d81 [email protected] github.com
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