Vulnerability · Published Jul 16, 2026 · Assigned by GitHub_M
CVE-2026-44453h2o is vulnerable to musl libc stack overflow
High 7.5
In plain English
A high-severity resource allocation without limits in h2o from h2o. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 42% of all known vulnerabilities).
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | h2o | no fix listed | DEBIAN-CVE-2026-44453 |
| Ubuntu:24.04:LTS | h2o | no fix listed | UBUNTU-CVE-2026-44453 |
Affected products (as reported)
Weakness: CWE-789, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84 x_refsource_CONFIRM
- https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181 x_refsource_MISC