🛡️ CVE-2026-44452 — h2o

🟡 CVSS 5.9 — Medium ✅ No Known Exploit CWE-125 NVD
5.9
CVSS Score
0 Low4 Medium7 High9 Critical10

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

Weakness class

CVE-2026-44452 is classified as CWE-125: Out-of-bounds Read. The code reads past the limits of a buffer, exposing adjacent memory contents or crashing the process.

Affected software

CVE-2026-44452 is recorded against 1 package.

  • h2o (fixed in 2026-05-29)

Timeline and source

Published on 16 July 2026 and last revised on 6 August 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com
github.com

Details

Severity MEDIUM
CVSS Score 5.9
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-125
Public Exploit ✅ No
Source NVD
Published 2026-07-16
Updated 2026-08-11
Modified 2026-08-06

Affected Packages

Software From version Fixed in
h2o — 2026-05-29

Similar Threats

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