Need

Secure object reutilization

Context

• Usage of PHP for server-side scripting and web development
• Usage of Cache for efficient data storage and retrieval
• Usage of Controller for handling request and response logic in a web application
• Usage of the User dependency for managing user data and authentication

Description

Non compliant code

        class UserController extends Controller
{
    public function show($id)
    {
        $user = Cache::get('user_'.$id);

        if (!$user) {
            $user = User::find($id);
            Cache::put('user_'.$id, $user, 60);
        }

        return view('user.profile', ['user' => $user]);
    }
}
        
        

The above code is vulnerable due to insecure service configuration
- object reutilization.

In this Laravel code snippet, we have a UserController with a show method. This method is used to display a user's profile. The function first checks if a user object is available in the cache. If it is, it retrieves the user object from the cache. If it is not, it retrieves the user from the database and stores it in the cache.

The vulnerability lies in the fact that the user object is stored in the cache and can be reused. If a malicious user gains access to the cache, they can reuse the user object for their own purposes. This can lead to a variety of security issues, such as identity theft or unauthorized access to user data.

Furthermore, the system does not validate that the user object, which is valid for one use only (displaying a user's profile), can be reused. This lack of validation further increases the risk of unauthorized object reutilization.

The system should include measures to ensure that objects, data, or information valid for one use cannot be reused. This could involve invalidating the cache after the user object is used, or implementing stricter access controls on the cache.

Steps

• Introduce a mechanism to invalidate the cache when the user data changes. This can be done by using events or observers in Laravel.
• When the user data is updated, the corresponding cache should be cleared. This ensures that stale data is not served from the cache.
• Consider using a time-based invalidation strategy. This means the cache would automatically be invalidated after a certain period of time.
• Ensure that the cache key is unique for each user. This prevents one user's data from being served to another user.
• Consider using Laravel's 'remember' method which automatically handles the retrieval and storage of items in the cache. This can help prevent object reutilization.

Compliant code

        class UserController extends Controller
{
    public function show($id)
    {
        $user = Cache::remember('user_'.$id, 60, function () use ($id) {
            return User::find($id);
        });

        return view('user.profile', ['user' => $user]);
    }
}

class User extends Model
{
    protected static function boot()
    {
        parent::boot();

        static::updated(function ($user) {
            Cache::forget('user_'.$user->id);
        });
    }
}
        
        

The updated code introduces a mechanism to invalidate the cache when the user data changes. This is done by using Laravel's model events. In the User model, we have added a static boot method. This method is called when the model is booted and allows us to attach model event listeners. In this case, we are attaching a listener to the updated event. This event is fired when a user record is updated in the database. The listener receives the updated user instance and uses it to clear the corresponding cache.

In the show method of the UserController, we have replaced the manual cache handling with Laravel's remember method. This method retrieves an item from the cache if it exists. If it does not exist, it executes the given closure, stores the result in the cache, and returns the result. The closure is given the user id and uses it to find the user in the database. This ensures that the cache is always serving fresh data and prevents object reutilization.

This solution ensures that the cache key is unique for each user and that stale data is not served from the cache. It also introduces a time-based invalidation strategy, as the remember method stores items in the cache for a given number of minutes. After this time, the cache is automatically invalidated.

References

• 387. Insecure service configuration - Object Reutilization