CVE-2026-44453 Details
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.
A denial-of-service vulnerability has been identified in the h2o HTTP server, which supports HTTP/1.x, HTTP/2, and HTTP/3. The issue arises when the server allocates memory for file paths using the alloca function, potentially leading to stack overflow. This vulnerability affects h2o versions prior to the patch in commit 6b5370d. When the memory allocation exceeds the default pthread stack limit of 128KB in musl libc, the server crashes with a segmentation fault while accessing the guard page.
Users can update to h2o version 6b5370d or later to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Jul 17, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-770 | Allocation of Resources Without Limits or Throttling | [email protected] |
| CWE-789 | Memory Allocation with Excessive Size Value | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| h2o h2o | < 2026-05-29 |
CPE
Remediation
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Change History
3 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Aug 6, 2026 | Initial Analysis | [email protected] |
| Jul 17, 2026 | CVE Modified | CISA-ADP |
| Jul 16, 2026 | New CVE Received | [email protected] |