CVE-2026-44452
h2o is vulnerable to heap overrun
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.
INFO
Published Date :
July 16, 2026, 11:16 p.m.
Last Modified :
Aug. 6, 2026, 1:56 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update h2o to commit 8dc37cb or later.
- Ensure SNI extension is handled correctly.
- Apply security patches promptly.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-44452.
| URL | Resource |
|---|---|
| https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3 | Patch |
| https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-44452 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-44452
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-44452 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-44452 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Reanalysis by [email protected]
Aug. 06, 2026
Action Type Old Value New Value Changed Reference Type GitHub, Inc.: https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq Types: Third Party Advisory GitHub, Inc.: https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq Types: Vendor Advisory -
Initial Analysis by [email protected]
Aug. 06, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:h2o:h2o:*:*:*:*:*:*:*:* versions up to (excluding) 2026-05-29 Added Reference Type GitHub, Inc.: https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq Types: Third Party Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-44452', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-17T14:03:32.725590Z'} -
New CVE Received by [email protected]
Jul. 16, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'h2o', 'product': 'h2o', 'versions': [{'status': 'affected', 'version': '< 8dc37cb'}]}] Added 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-125 Added CWE CWE-170 Added Reference https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3 Added Reference https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq