h2o is vulnerable to musl libc stack overflow
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-44453
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 4 Nov 2026, 02:35 UTC · Revision 1
Source evidence
h2o is vulnerable to musl libc stack overflow
core-osv · Original sourcePublished 16 Jul 2026, 23:04 UTC
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.
osv:CVE-2026-44453
Complete source record
{
"id": "921b8ee00a2d16f0223a990cc35d117bfa107bf419c58790d035757bd4f59f1b",
"url": "https://osv.dev/vulnerability/CVE-2026-44453",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "h2o is vulnerable to musl libc stack overflow",
"summary": "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.",
"evidence": "osv:CVE-2026-44453",
"products": [],
"severity": "high",
"structured": {
"id": "CVE-2026-44453",
"aliases": [
"CVE-2026-44453",
"GHSA-rf9v-m59p-mq84"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
}
],
"affected": [
{
"ranges": [
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"repo": "https://github.com/h2o/h2o",
"type": "GIT",
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{
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{
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"source": "REFERENCES_COMMIT"
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"versions": [
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"v1.7.0-beta5",
"v1.7.0-beta4",
"v1.7.0-beta3",
"v1.7.0-beta2",
"v1.7.0-beta1",
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"v1.5.0-beta2",
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"v1.4.2",
"v1.4.1",
"v1.4.0",
"v1.3.1",
"v1.3.0",
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"v1.2.0",
"v1.1.1",
"v1.1.0",
"v1.0.1",
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],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-44453.json"
}
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],
"modified": "2026-10-28T02:30:32.611735710Z",
"provider": "osv",
"references": [
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44453.json",
"https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84",
"https://nvd.nist.gov/vuln/detail/CVE-2026-44453",
"https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181"
],
"provider_metadata": {
"cwe_ids": [
"CWE-770",
"CWE-789"
],
"cna_assigner": "GitHub_M",
"unresolved_ranges": [
{
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{
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}
],
"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
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],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44453.json"
}
},
"related_cves": [
{
"value": "CVE-2026-44453",
"evidence": "/id"
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],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 499714,
"published_at": "2026-07-16T23:04:41.756+00:00"
}