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h2o: musl libc stack overflow (QPACK)

Type: advisorySources: OSV

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.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-55213
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 11:01 UTC · Revision 1

Source evidence

h2o: musl libc stack overflow (QPACK)

core-osv · Original source

Published 10 Jul 2026, 20:49 UTC

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.

osv:CVE-2026-55213
Complete source record
{
  "id": "4a295aecdebbc4294bed10f6b92750fdf28dc21600823df4366be3b8d1cd4aca",
  "url": "https://osv.dev/vulnerability/CVE-2026-55213",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "h2o: musl libc stack overflow (QPACK)",
    "summary": "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.",
    "evidence": "osv:CVE-2026-55213",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-55213",
      "aliases": [
        "CVE-2026-55213",
        "GHSA-432c-8xmj-frmq"
      ],
      "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": [
            {
              "repo": "https://github.com/h2o/h2o",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.7.0",
            "v1.7.0-beta5",
            "v1.7.0-beta4",
            "v1.7.0-beta3",
            "v1.7.0-beta2",
            "v1.7.0-beta1",
            "v1.6.0",
            "v1.6.0-beta2",
            "v1.6.0-beta1",
            "v1.5.3",
            "v1.5.2",
            "v1.5.1",
            "v1.5.0",
            "v1.5.0-beta4",
            "v1.5.0-beta3",
            "v1.5.0-beta2",
            "v1.5.0-beta1",
            "v1.4.2",
            "v1.4.1",
            "v1.4.0",
            "v1.3.1",
            "v1.3.0",
            "v1.3.0-beta1",
            "v1.2.0",
            "v1.1.1",
            "v1.1.0",
            "v1.0.1",
            "v0.9.2",
            "v0.9.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55213.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:28.211675043Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55213.json",
        "https://github.com/h2o/h2o/security/advisories/GHSA-432c-8xmj-frmq",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-55213",
        "https://github.com/h2o/h2o/commit/edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-789"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55213.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-55213",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 494797,
  "published_at": "2026-07-10T20:49:58.764+00:00"
}