# CVE-2026-44452

## Summary

- **CVE ID:** CVE-2026-44452
- **Severity:** MEDIUM
- **CVSS Score:** 5.9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** CWE-125, CWE-170
- **Published:** Jul 16, 2026
- **Last Modified:** Jul 17, 2026

## 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 Products

- h2o — h2o (< 8dc37cb)

## References

- [CNA](https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq)
- [CNA](https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.41%
- **EPSS Percentile:** 34.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._