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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181
https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84

Configurations

No configuration.

History

16 Jul 2026, 23:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-07-16 23:16

Updated : 2026-07-17 18:37

NVD link : CVE-2026-44453

Mitre link : CVE-2026-44453

CVE.ORG link : CVE-2026-44453

JSON object : View

Products Affected

No product.

CWE

CWE-770

Allocation of Resources Without Limits or Throttling

CWE-789

Memory Allocation with Excessive Size Value

{"id": "CVE-2026-44453", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-44453", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-07-17T14:29:07.563010Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "security-advisories@github.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 7.5, "attackVector": "NETWORK", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 3.9}]}, "affected": [{"source": "security-advisories@github.com", "affectedData": [{"vendor": "h2o", "product": "h2o", "versions": [{"status": "affected", "version": "< 6b5370d"}]}]}], "published": "2026-07-16T23:16:17.423", "references": [{"url": "https://github.com/h2o/h2o/commit/6b5370d9d09fcf83aa7620ddf77de1954a192181", "source": "security-advisories@github.com"}, {"url": "https://github.com/h2o/h2o/security/advisories/GHSA-rf9v-m59p-mq84", "source": "security-advisories@github.com"}], "vulnStatus": "Awaiting Analysis", "weaknesses": [{"type": "Secondary", "source": "security-advisories@github.com", "description": [{"lang": "en", "value": "CWE-770"}, {"lang": "en", "value": "CWE-789"}]}], "descriptions": [{"lang": "en", "value": "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."}], "lastModified": "2026-07-17T18:37:25.590", "sourceIdentifier": "security-advisories@github.com"}