CVE-2026-44435 | BDVDB-2026-348921 Detail

h2oquicly

Description#

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.

Impact#

Per CVSS v3.1: confidentiality impact none, integrity impact none, availability impact high. Attack vector: network.

Weaknesses#

CWE-617 Reachable Assertion
CWE-400 Uncontrolled Resource Consumption

References#

Exploit#

No public exploit known

History#

Version 12026-07-16Record published in the CVE List.
Version 22026-07-17Most recent update recorded in the CVE List.

Published

Published: 2026-07-16
Last modified: 2026-07-17

Vendor information

Vendor: h2o
Product: quicly

All h2o vulnerabilities

Score

7.5 High

EPSS

less than 1%, Very Low

Estimated chance of exploitation in the next 30 days. EPSS percentile: 42.3.

KEV

Not listed in the CISA Known Exploited Vulnerabilities catalog.

Impact

Denial of Service

Action

No specific action is recorded in the source data. Check the references for vendor guidance.

Affected Systems

Vulnerable
< 937d0e9
Fixed
Not stated

Scoring System

CVSS v4.0

Not available

CVSS v3.1

7.5 High

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

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

CVSS v3.0

Not available

CVSS v2

Not available

Source: CVE List v5 (record); CISA KEV (kev, action); FIRST EPSS (epss).