Case-sensitive excludedSubtrees name constraints cause Auth Bypass in crypto/x509

{
  "id": "e5931f5b697d5e0bb783eb9356ae806dc41650a275e6611407b5837ec437e891",
  "url": "https://osv.dev/vulnerability/GO-2026-4866",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Case-sensitive excludedSubtrees name constraints cause Auth Bypass in crypto/x509",
    "summary": "When verifying a certificate chain containing excluded DNS constraints, these constraints are not correctly applied to wildcard DNS SANs which use a different case than the constraint. This only affects validation of otherwise trusted certificate chains, issued by a root CA in the VerifyOptions.Roots CertPool, or in the system certificate pool.",
    "evidence": "osv:GO-2026-4866",
    "products": [
      {
        "name": {
          "value": "stdlib",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.26.2",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "GO-2026-4866",
      "aliases": [
        "BIT-golang-2026-33810",
        "CVE-2026-33810",
        "GO-2026-4866"
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "1.26.0-0"
                },
                {
                  "fixed": "1.26.2"
                }
              ]
            }
          ],
          "package": {
            "name": "stdlib",
            "purl": "pkg:golang/stdlib",
            "ecosystem": "Go"
          },
          "database_specific": {
            "source": "https://vuln.go.dev/ID/GO-2026-4866.json"
          },
          "ecosystem_specific": {
            "imports": [
              {
                "path": "crypto/x509",
                "symbols": [
                  "Certificate.Verify",
                  "dnsConstraints.query",
                  "newDNSConstraints"
                ]
              }
            ]
          }
        }
      ],
      "modified": "2026-10-14T10:56:59.645388910Z",
      "provider": "osv",
      "references": [
        "https://go.dev/cl/763763",
        "https://go.dev/issue/78332",
        "https://groups.google.com/g/golang-announce/c/0uYbvbPZRWU"
      ],
      "provider_metadata": {
        "url": "https://pkg.go.dev/vuln/GO-2026-4866",
        "review_status": "REVIEWED"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-33810",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 316141,
  "published_at": "2026-04-07T22:53:49+00:00"
}