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Insecure object reference - Files

Need​

Secure access control for files

Context​

  • Usage of PHP for server-side scripting and web development
  • Usage of the File module for file manipulation and operations

Description​

Non compliant code​

public function show($id)
{
    $file = File::find($id);
    return view('file.show', compact('file'));
}

In the above PHP code using Laravel framework, we have a method show() that is used to retrieve and display a file based on its identifier $id. The $id is directly used to find the file in the database without any authorization check.

This means any user who knows the $id of a file can access it, even if they are not the owner of the file or don't have the necessary permissions. This is an example of Insecure Direct Object Reference (IDOR) vulnerability, where the application exposes a reference to an internal implementation object.

In this case, the internal object is a file, and the reference is the file's $id. An attacker could potentially manipulate the $id to access or manipulate files of other users, leading to unauthorized information disclosure and potential data alteration.

Steps​

  • Implement an authorization check to verify if the user has the necessary permissions to access the file.
  • Use a secure reference map to replace direct object references. The map should associate the user's session with the IDs of the objects that the user is authorized to access.
  • Implement a mechanism to generate random identifiers for files, instead of using sequential or predictable identifiers. This will make it harder for an attacker to guess the identifiers of other files.
  • Log and monitor activities to detect and respond to unauthorized access attempts.

Compliant code​

public function show($id)
{
    $file = File::find($id);

    // Authorization check
    if (Auth::user()->cannot('view', $file)) {
        abort(403, 'Unauthorized action.');
    }

    return view('file.show', compact('file'));
}

The updated code includes an authorization check to ensure that the user has the necessary permissions to access the file. This is done using Laravel's built-in authorization system. The cannot method checks if the authenticated user does not have the 'view' ability for the given file. If the user does not have the necessary permissions, the application will abort with a 403 error.

In addition to this, you should also implement a secure reference map to replace direct object references. The map should associate the user's session with the IDs of the objects that the user is authorized to access. This will prevent unauthorized users from accessing or manipulating information of other users just by knowing the identifier that differentiates them.

Furthermore, consider implementing a mechanism to generate random identifiers for files, instead of using sequential or predictable identifiers. This will make it harder for an attacker to guess the identifiers of other files.

Finally, it's important to log and monitor activities to detect and respond to unauthorized access attempts. This will help you to identify potential security threats and take appropriate action to mitigate them.

References​

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