CVE-2026-44452: medium-severity vulnerability in h2o
h2o is vulnerable to heap overrun
Published · Updated
E-mail alert when it lands in KEV, gets a public PoC or its score goes up.
13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 5.9epss 0.4%
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:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected products
h2o · h2oRelated CVEs — h2o
In the same product, most dangerous first.
CVE-2021-43848HIGHUnititialized memory access in h2oEPSS 2.7%CVE-2023-30847HIGHH2O vulnerable to read from uninitialized pointer in the reverse proxy handlerEPSS 0.9%CVE-2023-50247LOWh2o QUIC state exhaustion DoSEPSS 0.9%CVE-2024-45403LOWH2O assertion failure when HTTP/3 requests are cancelledEPSS 0.7%CVE-2026-54340HIGHh2o has HTTP/2 state amplificationEPSS 0.5%CVE-2026-44453HIGHh2o is vulnerable to musl libc stack overflowEPSS 0.5%