CVE-2026-44453
highpriority · track · 0EPSS 0.005 · 42 %ileEUUSEPSS · scored 2026-10-28
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.
cvss
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 6.9–7.5
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
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affected products (2)
Products and version ranges known to be affected.
also known as (2)
Other names and identifiers for this entity.
sources
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references (6)
External citations — patches, advisories, analysis.
- https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181cnnvd
- https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84cnnvd
- https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181enisa_euvd
- https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84enisa_euvd
- https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181Patchnvd
- https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84Vendor Advisorynvd
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