Fix BFLA (Broken Function Level Authorization) in AdonisJS

BFLA (Broken Function Level Authorization) occurs when an application relies on client-side UI visibility or predictable URL structures instead of server-side validation. In AdonisJS, this typically happens when developers expose administrative routes or sensitive actions without attaching proper middleware or Bouncer policies. If a low-privileged user can hit an endpoint like /api/admin/delete-user just by guessing the path, your app is compromised. We fix this by implementing granular access control using AdonisJS Bouncer.

The Vulnerable Pattern

// start/routes.ts
Route.delete('/users/:id', 'UsersController.destroy')
// app/Controllers/Http/UsersController.ts
export default class UsersController {
public async destroy({ params, response }: HttpContextContract) {
// VULNERABILITY: No check to see if the requester has permission to delete users.
// Any authenticated (or even unauthenticated) user can delete any ID.
const user = await User.findOrFail(params.id)
await user.delete()
return response.status(204)
}
}

The Secure Implementation

To kill BFLA in AdonisJS, you must enforce the Principle of Least Privilege. The secure implementation uses 'AdonisJS Bouncer' to decouple authorization logic from the controller. The 'authorize' call ensures that even if the route is discovered by a non-admin, the server will throw a 403 Forbidden because the user's role doesn't meet the policy criteria. Always validate the 'actor' (the user making the request) against the 'action' (the function being called) on every sensitive endpoint.

// 1. Define a Policy: app/Policies/UserPolicy.ts
export default class UserPolicy extends BasePolicy {
  public async delete(user: User) {
    return user.role === 'admin'
  }
}
// 2. Controller with Authorization: app/Controllers/Http/UsersController.ts
export default class UsersController {
public async destroy({ bouncer, params, response }: HttpContextContract) {
const userToDelete = await User.findOrFail(params.id)
// SECURE: Explicitly authorize the action against the UserPolicy
await bouncer.with('UserPolicy').authorize('delete')

await userToDelete.delete()
return response.status(204)
}
}
// 3. Route Protection: start/routes.ts
Route.delete(‘/users/:id’, ‘UsersController.destroy’).middleware(‘auth’)

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The Vulnerable Pattern

The Secure Implementation

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