Vulnerability Description
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1, when h2o processes a QPACK instruction sent from the peer over HTTP/3, lib/http3/qpack.c might allocate an on-stack buffer as large as approximately 800 KB by calling alloca, which exceeds the default pthread stack size used by musl libc and causes the h2o server to crash with a segmentation fault while touching the guard page. This issue is fixed in commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/h2o/h2o/commit/edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1
- https://github.com/h2o/h2o/security/advisories/GHSA-432c-8xmj-frmq
FAQ
What is CVE-2026-55213?
CVE-2026-55213 is a vulnerability with a CVSS score of 7.5 (HIGH). h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1, when h2o processes a QPACK instruction sent from the peer over HTTP/3, lib...
How severe is CVE-2026-55213?
CVE-2026-55213 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-55213?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.