CVE-2026-44452 | h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and … | CVSS 5.9 MEDIUM

Description

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 8dc37cb, when h2o receives a ClientHello message over TLS or QUIC and it contains a zero-length SNI extension, the h2o server runs over the zero-length hostname while trying to copy the hostname, assuming that it is NULL-terminated. This is a potential denial-of-service attack vector in sense that it might trigger segmentation violation. This issue has been fixed by commit 8dc37cb.

Metadata

CVE ID: CVE-2026-44452
State: PUBLISHED
Assigner: GitHub_M
Reserved: 2026-05-06 15:49 UTC
Published: 2026-07-16 22:54 UTC
Last updated: 2026-07-16 22:54 UTC
Primary CWE: CWE-125
CWE-125: Out-of-bounds Read
Vendor / Product: h2o / h2o
Sources: cve.org · NVD

Severity & Metrics

5.9 MEDIUM CVSS 3.1

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

Affected products (1)

Vendor	Product	Platform	Versions
h2o	h2o	—	< 8dc37cb

Weakness (CWE)

CWE	Source	Description
CWE-125	cna	CWE-125: Out-of-bounds Read
CWE-170	cna	CWE-170: Improper Null Termination

CVSS scores (1)

Score	Severity	Version	Source	Vector
5.9	MEDIUM	3.1	cna	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References (2)

https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq
https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3 https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3