Identification Failures in Mongodb

Identification Failures, commonly categorized as Broken Object Level Authorization (BOLA) or Insecure Direct Object References (IDOR), occur when an API exposes internal object identifiers (like MongoDB _id fields) without properly verifying if the authenticated user has permission to access that specific object. MongoDB's flexible document model and query operators create unique attack surfaces for this vulnerability.

MongoDB-Specific Attack Patterns:

• Query Operator Abuse: MongoDB's query syntax includes operators like $ne (not equal), $gt (greater than), and $regex. Attackers manipulate path or ID parameters to inject these operators and bypass authorization checks. For example, a vulnerable endpoint like /api/users/<id> might be accessed with /api/users/5f50c31e8c4b3a2d1c8b4567 by changing the ID to /api/users/{"$ne":null} to retrieve all user documents if the query is constructed as db.users.find({_id: req.params.id}) without validation.
• Type Confusion: MongoDB's BSON type system allows the same value in different types (e.g., string "123" vs. integer 123) to be treated as distinct. An API that expects a string ObjectId but doesn't enforce type may allow an attacker to use an integer to match documents where _id is stored as a number, accessing unauthorized records.
• Server-Side JavaScript Injection (SSJI): The $where operator executes JavaScript on the database server. If user input is passed to $where unsanitized, an attacker can run arbitrary code to enumerate or exfiltrate data. CVE-2021-27906 highlights this in MongoDB Node.js driver versions before 3.6.10, where improper input handling could lead to SSJI.
• Array Operator Exploitation: Parameters that map to array fields can be manipulated with operators like $elemMatch to match unintended documents. For instance, /api/orders?user_id=5f50c31e8c4b3a2d1c8b4567 might be altered to /api/orders?user_id={"$elemMatch":{"role":"admin"}} to find admin-associated orders.

Real-World Code Path Example (Vulnerable Node.js/Express):

app.get('/api/profile/:userId', async (req, res) => {
  const user = await db.collection('users').findOne({ _id: req.params.userId });
  res.json(user);
});

Here, req.params.userId is directly used in the query. An attacker can supply a MongoDB query operator object (via URL encoding) to change the query semantics entirely.

Detecting MongoDB-specific Identification Failures requires testing how the API handles manipulated object identifiers and query operators. middleBrick's BOLA/IDOR and Input Validation checks are designed to probe these weaknesses in unauthenticated contexts.

Detection Methodology:

• Parameter Fuzzing with MongoDB Operators: The scanner sends requests where ID parameters are replaced with operator objects (e.g., {"$ne":null}, {"$regex":"^a"}) to see if the query returns multiple documents or unauthorized data. Successful exploitation often yields HTTP 200 with a JSON array instead of a single object, or reveals sensitive fields in error messages.
• Type Confusion Testing: middleBrick attempts to submit IDs in alternate types (integer, float, string representations) to identify cases where the database driver performs implicit type coercion, leading to access of records with mismatched _id types.
• SSJI Probe: The scanner injects $where payloads like {"$where":"1==1"} or {"$where":"this.email != null"} into parameters that might be used in queries, looking for delayed responses (indicative of JavaScript execution) or data leakage.
• OpenAPI/Swagger Analysis: When an OpenAPI spec is provided, middleBrick resolves $ref and identifies parameters marked as path or query that likely reference object IDs (e.g., named userId, orderId). These are prioritized for IDOR testing.

Using middleBrick for Detection:

From the terminal, scan an API endpoint to receive a detailed report:

middlebrick scan https://api.example.com/v1/users/5f50c31e8c4b3a2d1c8b4567

The report will flag any BOLA/IDOR findings specific to MongoDB query manipulation, assign a severity (e.g., High), and include the exact request that demonstrated the vulnerability. The GitHub Action can be configured to fail a pull request if a new BOLA finding appears:

- name: API Security Scan
  uses: middlebrick/github-action@v1
  with:
    api_url: ${{ env.STAGING_API_URL }}
    fail_on_risk_score: 'B'

This integrates continuous detection into your CI/CD pipeline, preventing deployments with newly introduced MongoDB IDOR flaws.

Remediation focuses on enforcing strict authorization at the application layer and using MongoDB driver features safely. Never rely on client-side checks or obscurity of IDs.

1. Use Parameterized Queries with Type-Safe IDs:

Always convert incoming ID parameters to the correct BSON type (ObjectId) and use driver methods that separate query structure from data. In Node.js with the native MongoDB driver:

const { ObjectId } = require('mongodb');

app.get('/api/profile/:userId', async (req, res) => {
  // Validate and cast to ObjectId
  const userId = new ObjectId(req.params.userId);

  // Authorize: ensure req.user.id matches userId (or has admin role)
  if (!req.user || req.user.id.toString() !== userId.toString()) {
    return res.status(403).json({ error: 'Forbidden' });
  }

  const user = await db.collection('users').findOne({ _id: userId });
  res.json(user);
});

In Python with PyMongo:

from bson import ObjectId

@app.route('/api/profile/')
def get_profile(userId):
    try:
        user_oid = ObjectId(userId)
    except Exception:
        abort(400, 'Invalid user ID')

    # Authorize current_user.id == user_oid
    if current_user.id != user_oid and not current_user.is_admin:
        abort(403)

    user = db.users.find_one({'_id': user_oid})
    return jsonify(user)

2. Avoid Dynamic Query Construction: Never interpolate user input directly into query strings or objects. If you must build dynamic queries, use an allowlist of permitted fields and operators.

// UNSAFE - do not do
const query = { _id: req.params.userId, status: req.query.status }; // status could be {$ne: 'active'}

// SAFER - whitelist
const allowedStatuses = ['active', 'inactive'];
const status = allowedStatuses.includes(req.query.status) ? req.query.status : null;
const query = { _id: userId };
if (status) query.status = status;

3. Disable $where and JavaScript Execution: The $where operator should be disabled in production if possible. Modern MongoDB drivers do not support it by default in many contexts, but ensure your ODM (like Mongoose) does not inadvertently allow it.

4. Implement Schema-Level Authorization: For applications with complex permission models, consider using MongoDB Realm (now called MongoDB Atlas App Services) or implement middleware that checks document-level permissions before returning data. For example, store an ownerId field in each document and always query with { _id: id, ownerId: currentUser.id }.

5. Principle of Least Privilege for Database Users: The application's MongoDB user should have only find permission on necessary collections, and queries should be scoped by the application logic, not by database roles alone. However, application-level checks are still mandatory.