What is CVE-2026-55213?

CVE-2026-55213 is a high-severity vulnerability in H2o, classified under CWE-789. CVSS score: 7.5/10. Published 2026-07-10.

How severe is CVE-2026-55213?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in H2o

CVE-2026-55213

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-sta…

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

H2o — versions < edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1

Weakness classification (CWE)

CWE-789

References

security-advisories@github.com (x_refsource_MISC)
security-advisories@github.com (x_refsource_CONFIRM)

Frequently asked questions

What is CVE-2026-55213?: CVE-2026-55213 is a high-severity vulnerability in H2o, classified under CWE-789. CVSS score: 7.5/10. Published 2026-07-10.
How severe is CVE-2026-55213?: High severity. CVSS v3 base score is 7.5 out of 10.