What is CVE-2026-44453?
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.
The record classifies CVE-2026-44453 under weakness classes CWE-789, CWE-770. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 81 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 7.5 — HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 3.8/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-07-16
Is CVE-2026-44453 being exploited?
It currently carries a trending score of 30 in the Threadlinqs vulnerability feed.
Affected products and versions
- h2o: h2o
How to fix CVE-2026-44453
No vendor patch reference has been recorded for CVE-2026-44453 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.
Threat activity tracking CVE-2026-44453
No threat campaign in the Threadlinqs corpus currently references CVE-2026-44453, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.
Sources
Enriched from CVE.org, NVD. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.