Fix BOLA (Broken Object Level Authorization) in Meteor

BOLA (Broken Object Level Authorization) is the primary attack vector in Meteor applications. It occurs when a Method or Publication trusts a client-supplied ID without verifying that the requesting user has the rights to access that specific object. In Meteor's reactive environment, failing to scope your MongoDB selectors to the 'this.userId' context allows any authenticated user to modify or view any document by simply guessing or iterating its UUID.

The Vulnerable Pattern

Meteor.methods({
  'profile.update'(profileId, updatedData) {
    // VULNERABLE: Trusting the client-provided profileId blindly
    // An attacker can pass any profileId and overwrite someone else's data
    Profiles.update(profileId, { $set: updatedData });
  }
});
Meteor.publish(‘secretNotes’, function(noteId) {
// VULNERABLE: No ownership check in the publication
return Notes.find({ _id: noteId });
});

The Secure Implementation

To kill BOLA in Meteor, you must implement 'Scope-Based Querying'. Never use a client-provided ID as the sole key in a database operation. Instead, always combine the document ID with 'this.userId' in your MongoDB selector. This ensures that even if an attacker provides a valid ID for an object they don't own, the query returns zero results. Additionally, use the 'check' package to prevent NoSQL injection and always verify the existence of 'this.userId' before executing logic to prevent anonymous escalation.

Meteor.methods({
  'profile.update'(profileId, updatedData) {
    check(profileId, String);
    check(updatedData, Object);
if (!this.userId) {
  throw new Meteor.Error('not-authorized');
}

// SECURE: Force the selector to include the current user's ID
const result = Profiles.update(
  { _id: profileId, ownerId: this.userId },
  { $set: { bio: updatedData.bio } }
);

if (result === 0) {
  throw new Meteor.Error('access-denied', 'Object not found or unauthorized');
}
}
});
Meteor.publish(‘secretNotes’, function(noteId) {
check(noteId, String);
if (!this.userId) return this.ready();
// SECURE: Scope the cursor to the authenticated user
return Notes.find({ _id: noteId, ownerId: this.userId });
});

About this page

Framework notes in /guides are generated sketches kept for URL stability. They are not human pentest reports and they are not GuardAPI scan output. The product is a GET-only BOLA merge gate. Maintained by GuardAPI. Questions: support@guard-api.com