CVE-2026-44452

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.

CVSS Vector

References

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