Fix BFLA (Broken Function Level Authorization) in Grape

BFLA (Broken Function Level Authorization) in Grape APIs occurs when sensitive endpoints rely on 'security by obscurity' or assume that being logged in (authentication) is the same as having permission (authorization). Attackers exploit this by hitting administrative routes using low-privileged tokens. In Grape, this usually happens because developers forget to implement role-based access control (RBAC) helpers on specific resource blocks.

The Vulnerable Pattern

class UsersAPI < Grape::API
  resource :users do
    # VULNERABLE: Any authenticated user can delete any other user
    # because there is no role check.
    delete ':id' do
      authenticate!
      User.find(params[:id]).destroy
    end
  end
end

The Secure Implementation

To kill BFLA, stop trusting the token alone. The fix involves implementing an authorization layer—either via custom helpers or integrating gems like Pundit/CanCanCan. In the secure example, we define an `authorize_admin!` helper that explicitly checks the user's role before the logic executes. For complex APIs, use Grape's `before` blocks to apply authorization checks across entire namespaces, ensuring that administrative functions are physically unreachable by non-privileged actors.

class UsersAPI < Grape::API
  helpers do
    def authorize_admin!
      error!('403 Forbidden', 403) unless current_user.admin?
    end
  end
resource :users do
desc ‘Delete a user (Admin only)’
delete ‘:id’ do
authenticate!
authorize_admin!
User.find(params[:id]).destroy
end
end
end