CVE-2026-44453: high-severity vulnerability in h2o
h2o is vulnerable to musl libc stack overflow
Published · Updated
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 7.5epss 0.5%
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:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected products
h2o · h2oRelated CVEs — h2o
In the same product, most dangerous first.
CVE-2021-43848HIGHUnititialized memory access in h2oEPSS 2.7%CVE-2023-30847HIGHH2O vulnerable to read from uninitialized pointer in the reverse proxy handlerEPSS 0.9%CVE-2023-50247LOWh2o QUIC state exhaustion DoSEPSS 0.9%CVE-2024-45403LOWH2O assertion failure when HTTP/3 requests are cancelledEPSS 0.7%CVE-2026-54340HIGHh2o has HTTP/2 state amplificationEPSS 0.5%CVE-2026-55213HIGHh2o: musl libc stack overflow (QPACK)EPSS 0.5%