Bola Idor in Flask with Cockroachdb

Broken Object Level Authorization (BOLA) occurs when an API fails to enforce access controls at the object level, allowing one user to view or modify another user’s resources. In a Flask application using CockroachDB, this risk is shaped by how identifiers are handled, how queries are constructed, and how sessions or tokens are validated.

Consider a Flask route like /users/<user_id>/profile. If the route uses a raw user_id from the URL to build a CockroachDB SQL string without verifying that the authenticated user owns that ID, an attacker can change the ID to access another account. CockroachDB’s SQL engine will return data if the query is valid, even if the requester should not see it. A vulnerable pattern looks like this:

import sqlite3
from flask import request, jsonify

@app.route("/users/<int:user_id>/profile")
def get_profile(user_id):
    conn = sqlite3.connect("/tmp/cockroachdb/secure.db")
    cur = conn.cursor()
    cur.execute(f"SELECT id, display_name, email FROM profiles WHERE id = {user_id}")
    row = cur.fetchone()
    return jsonify(row)

Here, the lack of ownership check or proper scoping allows horizontal BOLA: any authenticated user can enumerate profiles by incrementing user_id. Introducing authentication tokens or session cookies without validating scope does not automatically prevent this; the query must enforce tenant boundaries.

In a CockroachDB-backed Flask service, BOLA is often exposed through insecure use of primary keys, lack of tenant ID scoping, or failure to validate relationships before returning data. For example, a “list your orders” endpoint might use a simple SELECT * FROM orders WHERE user_id = ? but if the caller can supply any user_id parameter, they can probe other users’ orders. CockroachDB does not inherently enforce row-level permissions; that responsibility sits with the application logic and query design.

Common root causes include:

• Using sequential or guessable IDs without access checks.
• Relying on frontend controls alone to hide data.
• Missing or inconsistent tenant/context checks in JOINs or subqueries.
• Overprivileged database roles that allow broad reads, making scoping a developer concern.

Because CockroachDB supports distributed SQL and secondary indexes, attackers can efficiently enumerate resources if BOLA exists. A compromised low-privilege account can leverage predictable IDs to build a complete dataset unless the API consistently applies authorization context at the query layer.

To mitigate BOLA in Flask with CockroachDB, enforce strict ownership checks and scope every query to the authenticated subject. Avoid constructing SQL via string interpolation; use parameterized queries and explicit tenant/context validation.

First, model your data with a tenant-aware schema. Include a user_id (or tenant_id) on each row that must be protected, and include it in every relevant query:

-- Example schema in CockroachDB
CREATE TABLE profiles (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    user_id UUID NOT NULL,
    display_name STRING,
    email STRING,
    INDEX idx_user_id (user_id)
);

In Flask, bind the current user’s ID from authentication (e.g., JWT subject or session) and use it to scope queries. With a CockroachDB Python driver such as psycopg2 or cockroachdb, prefer parameterized statements:

from flask import request, jsonify
import psycopg2
from psycopg2 import sql

def get_db_conn():
    return psycopg2.connect(
        host="localhost",
        port=26257,
        dbname="securebank",
        user="app_user",
        password="strongpass"
    )

@app.route("/users/<int:user_id>/profile")
def get_profile(user_id):
    auth_user_id = get_authenticated_user_id()  # e.g., from JWT/session
    if auth_user_id != user_id:
        return jsonify({"error": "forbidden"}), 403
    conn = get_db_conn()
    try:
        with conn.cursor() as cur:
            cur.execute(
                sql.SQL("SELECT id, display_name, email FROM profiles WHERE id = %s AND user_id = %s"),
                [user_id, auth_user_id]
            )
            row = cur.fetchone()
            if row is None:
                return jsonify({"error": "not found"}), 404
            return jsonify({"id": row[0], "display_name": row[1], "email": row[2]})
    finally:
        conn.close()

This approach ensures that even if an attacker changes user_id, the server compares it to the authenticated subject and rejects mismatches. It also uses CockroachDB-compatible parameterization, avoiding SQL injection while providing row-level scoping.

@app.route("/orders")
def list_orders():
    auth_user_id = get_authenticated_user_id()
    conn = get_db_conn()
    try:
        with conn.cursor() as cur:
            cur.execute(
                sql.SQL("SELECT id, total, status FROM orders WHERE user_id = %s ORDER BY created_at DESC"),
                [auth_user_id]
            )
            rows = cur.fetchall()
            return jsonify([{"id": r[0], "total": r[1], "status": r[2]} for r in rows])
    finally:
        conn.close()