🛡️ CVE-2026-44453 — h2o

🟠 CVSS 7.5 — High ✅ No Known Exploit CWE-770 NVD
7.5
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 6b5370d, h2o is vulnerable to a Denial of Service attack when calling alloca under certain conditions. When serving static files, h2o builds the file path on stack, by calling alloca. The maximum size of the memory allocated using alloca can be as huge as ~600KB, which exceeds the default pthread stack size used by musl libc (128KB). If the amount of memory allocated by alloca exceeds the stack size, the h2o server crashes with a segmentation fault, while it tries to touch the guard page. This issue has been fixed by commit 6b5370d.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, 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-2026-44453 is classified as CWE-770: Allocation of Resources Without Limits. Resources are allocated on request with no cap, so a client can exhaust them.

Affected software

CVE-2026-44453 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 HIGH
CVSS Score 7.5
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-770
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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