Vulnerability · Published Jul 16, 2026 · Assigned by GitHub_M
CVE-2026-44452h2o is vulnerable to heap overrun
Medium 5.9
In plain English
A medium-severity out-of-bounds read 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 0.4% (higher than 36% 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 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | h2o | no fix listed | DEBIAN-CVE-2026-44452 |
| Ubuntu:24.04:LTS | h2o | no fix listed | UBUNTU-CVE-2026-44452 |
Affected products (as reported)
Weakness: CWE-125, CWE-170 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq x_refsource_CONFIRM
- https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3 x_refsource_MISC