Vulnerability Details CVE-2026-44452
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 16.4%
CVSS Severity
CVSS v3 Score 5.9