CVE-2026-55213 | h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and … | CVSS 7.5 HIGH

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.

Metadata

CVE ID: CVE-2026-55213
State: PUBLISHED
Assigner: GitHub_M
Reserved: 2026-06-16 16:16 UTC
Published: 2026-07-10 20:49 UTC
Last updated: 2026-07-10 20:49 UTC
Primary CWE: CWE-789
CWE-789: Memory Allocation with Excessive Size Value
Vendor / Product: h2o / h2o
Sources: cve.org · NVD

Severity & Metrics

7.5 HIGH CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products (1)

Vendor	Product	Platform	Versions
h2o	h2o	—	< edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1

Weakness (CWE)

CWE	Source	Description
CWE-789	cna	CWE-789: Memory Allocation with Excessive Size Value

CVSS scores (1)

Score	Severity	Version	Source	Vector
7.5	HIGH	3.1	cna	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References (2)

https://github.com/h2o/h2o/security/advisories/GHSA-432c-8xmj-frmq https://github.com/h2o/h2o/security/advisories/GHSA-432c-8xmj-frmq
https://github.com/h2o/h2o/commit/edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1 https://github.com/h2o/h2o/commit/edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1