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Inadequate file size control

Need​

Implementation of file size validation and restriction

Context​

  • Requirement of PHP 5.6 or later for running the application
  • Usage of Request for making HTTP requests
  • Usage of public_path for specifying the public directory path in a web application

Description​

Non compliant code​

public function uploadFile(Request $request)
{
    if($request->hasFile('file')) {
        $file = $request->file('file');
        $name = time().'.'.$file->getClientOriginalExtension();
        $destinationPath = public_path('/uploads');
        $file->move($destinationPath, $name);
    }
}

The above PHP code is a function in Laravel that handles file uploads. It checks if a file is present in the request using the $request->hasFile('file') method. If a file is present, it retrieves the file from the request, generates a new name for the file based on the current timestamp and the file's original extension, sets a destination path for the file to be stored, and then moves the file from the temporary path to the destination path.

The vulnerability in this code is that it does not perform any checks on the size of the file being uploaded. This means that a user could potentially upload a very large file, which could fill up the server's storage, slow down the server, or even crash the server. This is a type of Denial of Service (DoS) attack.

Steps​

  • First, you need to validate the file size before processing the upload. You can use the 'getSize' method on the file object to get the size of the file in bytes.
  • Next, define a maximum file size limit. This limit should be set according to your application's requirements and the server's capacity.
  • Then, compare the size of the uploaded file with the defined limit. If the file size exceeds the limit, reject the upload and return an error message to the user.
  • Finally, only proceed with the file upload if the file size is within the defined limit. This will ensure that your server is not overwhelmed by large files.

Compliant code​

public function uploadFile(Request $request)
{
    // Define maximum file size limit in bytes (e.g., 2MB)
    $maxFileSize = 2 * 1024 * 1024;

    if($request->hasFile('file')) {
        $file = $request->file('file');

        // Check file size
        if ($file->getSize() > $maxFileSize) {
            return response()->json(['error' => 'File size exceeds the maximum limit'], 400);
        }

        $name = time().'.'.$file->getClientOriginalExtension();
        $destinationPath = public_path('/uploads');
        $file->move($destinationPath, $name);
    }
}

The updated code now includes a check for the size of the uploaded file.

First, we define a maximum file size limit in bytes. In this example, the limit is set to 2MB, but you can adjust this according to your application's requirements and the server's capacity.

Next, we use the getSize method on the file object to get the size of the uploaded file in bytes.

We then compare the size of the uploaded file with the defined limit. If the file size exceeds the limit, we reject the upload and return an error message to the user. This is done using the response method to return a JSON response with a 400 status code (indicating a bad request) and an error message.

Finally, if the file size is within the defined limit, we proceed with the file upload as before. This ensures that the server is not overwhelmed by large files, thus fixing the vulnerability.

References​

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