Insecure Direct Object References

WSTG - Latest | OWASP Foundation
What makes this attack very common is essentially the lack of a solid access control system on the back-end
As web applications store users' files and information
they may use sequential numbers or user IDs to identify each item
Suppose the web application lacks a robust access control mechanism and exposes direct references to files and resources
We may access other users' files and information by simply guessing or calculating their file IDs.

IDOR Mitigation

match /api/profile/{userId} {
    allow read, write: if user.isAuth == true
    && (user.uid == userId || user.roles == 'admin');
}