CVE-2026-44453
h2o is vulnerable to musl libc stack overflow
Description
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 6b5370d, h2o is vulnerable to a Denial of Service attack when calling alloca under certain conditions. When serving static files, h2o builds the file path on stack, by calling alloca. The maximum size of the memory allocated using alloca can be as huge as ~600KB, which exceeds the default pthread stack size used by musl libc (128KB). If the amount of memory allocated by alloca exceeds the stack size, the h2o server crashes with a segmentation fault, while it tries to touch the guard page. This issue has been fixed by commit 6b5370d.
INFO
Published Date :
July 16, 2026, 11:16 p.m.
Last Modified :
Aug. 6, 2026, 1:25 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 | HIGH | [email protected] |
Solution
- Update h2o to version with commit 6b5370d applied.
- Monitor server stability after update.
- Review system stack size limits.
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-2026-44453.
| URL | Resource |
|---|---|
| https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181 | Patch |
| https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84 | 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-2026-44453 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-2026-44453
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-2026-44453 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-44453 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.
-
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/6b5370d9d09fcf83aa7620ddf77de1954a192181 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84 Types: Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-44453', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-17T14:29:07.563010Z'} -
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': '< 6b5370d'}]}] Added Description h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 6b5370d, h2o is vulnerable to a Denial of Service attack when calling alloca under certain conditions. When serving static files, h2o builds the file path on stack, by calling alloca. The maximum size of the memory allocated using alloca can be as huge as ~600KB, which exceeds the default pthread stack size used by musl libc (128KB). If the amount of memory allocated by alloca exceeds the stack size, the h2o server crashes with a segmentation fault, while it tries to touch the guard page. This issue has been fixed by commit 6b5370d. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-770 Added CWE CWE-789 Added Reference https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181 Added Reference https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84