MCP Registry: Unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-local IPv6 addresses, bypassing private-address allowlist

{
  "id": "c5c31153933e90c7e0d04c5a231068c6d05cae95b45c60e6650c085f67bd8d17",
  "url": "https://osv.dev/vulnerability/CVE-2026-44430",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "MCP Registry: Unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-local IPv6 addresses, bypassing private-address allowlist",
    "summary": "The MCP Registry provides MCP clients with a list of MCP servers, like an app store for MCP servers. Prior to 1.7.7, the Registry's HTTP-based namespace verification (POST /v0/auth/http, POST /v0.1/auth/http) uses safeDialContext (internal/api/handlers/v0/auth/http.go:67-110) to refuse dialling private/internal addresses when fetching the well-known public-key file from a publisher-supplied domain. The blocklist (isBlockedIP, lines 125-133) relies entirely on Go stdlib's IsLoopback / IsPrivate / IsLinkLocalUnicast / IsMulticast / IsUnspecified plus a manual CGNAT range. None of these cover IPv6 6to4 (2002::/16), NAT64 (64:ff9b::/96 and 64:ff9b:1::/48 per RFC 8215), or deprecated site-local (fec0::/10) — all of which encode arbitrary IPv4 in the address bits and tunnel to RFC1918 / cloud-metadata services on dual-stack / NAT64-enabled hosts. This vulnerability is fixed in 1.7.7.",
    "evidence": "osv:CVE-2026-44430",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-44430",
      "aliases": [
        "CVE-2026-44430",
        "GHSA-r48c-v28r-pf6v",
        "GO-2026-5607"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/modelcontextprotocol/registry",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "f5f40bd98084466eaf18fe48ea62a0d534caa774"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.7.7"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "cpe": "cpe:2.3:a:lfprojects:mcp_registry:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.7.7"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.7.6",
            "v1.7.5",
            "v1.7.4",
            "v1.7.3",
            "v1.7.2",
            "v1.7.1",
            "v1.7.0",
            "v1.6.0",
            "v1.5.0",
            "v1.4.1",
            "v1.4.0",
            "v1.3.10",
            "v1.3.9",
            "v1.3.8",
            "v1.3.7",
            "v1.3.6",
            "v1.3.5",
            "v1.3.4",
            "v1.3.3",
            "v1.3.2",
            "v1.3.1",
            "v1.3.0",
            "v1.2.3",
            "v1.2.2",
            "v1.2.1",
            "v1.2.0",
            "v1.1.0",
            "v1.0.0",
            "v0.0.3",
            "v0.0.2",
            "v0.0.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-44430.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:38.892755871Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44430.json",
        "https://github.com/modelcontextprotocol/registry/security/advisories/GHSA-r48c-v28r-pf6v",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-44430"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-918"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44430.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-44430",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 506179,
  "published_at": "2026-05-14T21:02:40.738+00:00"
}