HIGH broken access controlsinatramongodb

Broken Access Control in Sinatra with Mongodb

Broken Access Control in Sinatra with Mongodb — how this specific combination creates or exposes the vulnerability

Broken Access Control occurs when application logic fails to enforce proper authorization between different users or roles. In a Sinatra app using Mongodb, this often maps to the BOLA/IDOR checks in middleBrick’s 12 security checks. A typical pattern is trusting a client-supplied identifier (e.g., user_id from params) to build a query without verifying that the requesting user is allowed to access that resource.

For example, consider a route that fetches a user profile by ID:

get '/profiles/:user_id' do
  user = Mongoid.default_client[:users].find(_id: params[:user_id]).first
  # missing check that current_user can view this profile
  user.to_json
end

If the route does not compare params[:user_id] with the authenticated user’s ID or role, an attacker can iterate through valid ObjectIds and access other users’ profiles. This is an IDOR (Insecure Direct Object Reference) pattern and is one of the 12 parallel checks middleBrick runs, specifically under BOLA/IDOR and Property Authorization.

Sinatra does not provide an authorization layer by default, so developers must explicitly enforce ownership or role checks. With Mongodb, queries that do not scope by tenant or ownership (e.g., missing $match-style filters in aggregation or missing user_id in the filter) can unintentionally expose data. Additionally, if route parameters are not validated, an attacker may exploit type confusion or injection to bypass intended access restrictions, which feeds into Input Validation findings. middleBrick’s unauthenticated scan can detect such endpoints by analyzing the OpenAPI spec and runtime behavior, identifying missing authorization checks that would otherwise be missed.

Common root causes specific to Sinatra + Mongodb include:

Using path or query parameters directly in a filter without scoping to the requesting user or tenant.
Relying on UI-level hiding rather than server-side enforcement.
Overly broad read permissions in Mongodb roles or connection strings that allow unverified reads across collections.

These issues are surfaced in the middleBrick report as high-severity findings with remediation steps, because they can lead to mass data exposure in APIs that expose sensitive user or organizational data.

Mongodb-Specific Remediation in Sinatra — concrete code fixes

To fix Broken Access Control in Sinatra with Mongodb, enforce ownership or role-based checks in every query that accesses user-specific or tenant-specific data. Below are concrete, working examples.

1. Scope queries to the authenticated user

Always include the user identifier from the session or token in your filter. Do not rely on client-supplied IDs alone.

# Assume current_user has _id set by your auth logic (e.g., via sinatra-flash or a token verifier)
get '/profiles/:user_id' do
  halt 403, 'Forbidden' unless params[:user_id] == current_user[:_id].to_s
  user = Mongoid.default_client[:users].find(_id: params[:user_id]).first
  user ? user.to_json : halt(404, 'Not found')
end

2. Use parameterized aggregation with a $match on ownership

If using aggregation pipelines, include a match stage that restricts by user or tenant.

pipeline = [
  { '$match' => { 'user_id' => BSON::ObjectId.from_string(current_user[:_id]) } },
  { '$project' => { 'name' => 1, 'email' => 1 } }
]
results = Mongoid.default_client[:logs].aggregate(pipeline).to_a
# Only logs belonging to the current_user are returned

3. Enforce role-based access with RBAC checks before sensitive operations

allowed_roles = ['admin', 'manager']
user = Mongoid.default_client[:users].find(_id: current_user[:_id]).first
halt 403, 'Insufficient permissions' unless user && (allowed_roles & user['roles']).any?

# Proceed with privileged action

4. Validate and sanitize input before using in queries

Prevent injection and malformed IDs by validating parameter formats.

id_param = params[:user_id]
unless id_param =~ /^[0-9a-fA-F]{24}$/
  halt 400, 'Invalid ID format'
end
user = Mongoid.default_client[:users].find(_id: id_param).first

5. Apply tenant scoping for multi-tenant apps

If your data includes a tenant_id, ensure every query includes it.

tenant_id = current_user[:tenant_id]
records = Mongoid.default_client[:documents].find(tenant_id: tenant_id, visibility: 'public').to_a

6. Use least-privilege database roles

Configure your Mongodb connection string and user roles to grant only the permissions needed (e.g., readWrite on specific collections) rather than broad admin access. This limits the impact of any residual access control flaws.

After applying these fixes, re-run scans with middleBrick (CLI: middlebrick scan <url>, Dashboard, or GitHub Action) to confirm that the findings under BOLA/IDOR and Property Authorization are cleared. These changes align with OWASP API Top 10 A1:2023 broken access control and help prevent unauthorized data access without relying on automatic fixes.

Frequently Asked Questions

Why does middleBrick flag routes that use user_id from params without comparing to the authenticated user?

Because it matches the BOLA/IDOR pattern: an attacker can modify the parameter to access other users' data. MiddleBrick flags missing ownership or role checks as a high-severity finding and recommends scoping queries to the requesting user.

Can I rely on middleware that sets current_user to prevent these issues?

Middleware that sets current_user is helpful, but you must still enforce checks in each route or query. MiddleBrick’s scans verify that filters in Mongodb queries include user or tenant identifiers; simply having a current_user variable is not sufficient to pass authorization checks.

Broken Access Control in Sinatra with Mongodb