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Insufficient data authenticity validation - Checksum verification

Need​

Ensure data authenticity through proper checksum verification

Context​

  • Usage of PHP for server-side scripting and web development
  • Usage of file_get_contents for reading the contents of a file

Description​

Non compliant code​

<?php

// Load the resource from an external server
$resource = file_get_contents('http://external-server.com/resource.txt');

// Use the resource directly without any validation
echo $resource;

?>

In the above PHP code, the application is loading a resource from an external server using the file_get_contents function. This function is used to read a file into a string.

The vulnerability here is that there is no validation of the integrity of the resource being loaded. The application reads the resource and uses it directly without checking if the resource has been tampered with during the transfer from the external server. This is a risk as an attacker could modify the resource on the external server or during the transfer, which could lead to various security issues such as data corruption, information disclosure, or code execution.

In the context of the Laravel framework, this could be a backend operation where the application is loading resources that are used for various functionalities of the application. The lack of integrity checks could lead to serious security issues as mentioned above. It's crucial to always validate the authenticity of data loaded from external sources to ensure the security and reliability of the application.

Steps​

  • Introduce a checksum verification process for the resource loaded from the external server.
  • Calculate the checksum of the resource immediately after it is loaded.
  • Store a known good checksum of the resource for comparison.
  • Compare the calculated checksum with the known good checksum.
  • If the checksums match, proceed with using the resource.
  • If the checksums do not match, handle the error appropriately, such as by not using the resource, logging the error, and/or alerting an administrator.

Compliant code​

<?php

// Load the resource from an external server
$resource = file_get_contents('http://external-server.com/resource.txt');

// Calculate the checksum of the resource
$resourceChecksum = md5($resource);

// Known good checksum of the resource
$knownGoodChecksum = 'known_good_checksum_here';

// Compare the calculated checksum with the known good checksum
if ($resourceChecksum === $knownGoodChecksum) {
    // If the checksums match, proceed with using the resource
    echo $resource;
} else {
    // If the checksums do not match, handle the error appropriately
    error_log('Resource checksum does not match the known good checksum');
    // Optionally, alert an administrator or take other action
}

?>

The updated code introduces a checksum verification process for the resource loaded from the external server. This is done to validate the integrity of the resource and ensure it has not been tampered with.

Immediately after the resource is loaded, its checksum is calculated using the md5() function. This calculated checksum is then compared with a known good checksum of the resource. If the checksums match, it means the resource has not been tampered with and it is safe to use. The resource is then echoed out as before.

If the checksums do not match, it means the resource may have been tampered with. In this case, an error is logged using the error_log() function. This is a basic way of handling the error. Depending on the requirements of your application, you may want to take additional action, such as alerting an administrator or stopping the execution of the script.

References​

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