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Vulnerability record · CVE-2026-44452 · published 16 July 2026

CVE-2026-44452: H2o out-of-bounds read vulnerability

H2o · H2o

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.

5.9 CVSS 3.1 Medium EPSS 0.41% · top 66.8% CWE-125 · Out-of-bounds readCWE-170 · CWE-170
5.9CVSS 3.1 base score
0.41%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
6 Aug 2026Last modified by NVD

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:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3 Patch
https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq Vendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-44452), CISA KEV, FIRST EPSS (scores of 2026-10-05). This page is refreshed as NVD updates the record.