This exploit requires Metasploit to have a FQDN and the ability to run a payload web server on port 80, 443, or 8080. The FQDN must also not resolve to a reserved address (192/172/127/10). The server must also respond to a HEAD request for the payload, prior to getting a GET request. This exploit leverages an authenticated improper input validation in WordPress plugin Popular Posts versions 5.3.2 and below. The exploit chain is rather complicated. Authentication is required and gd for PHP is required on the server. Then the Popular Post plugin is reconfigured to allow for an arbitrary URL for the post image in the widget. A post is made, then requests are sent to the post to make it more popular than the previous #1 by 5. Once the post hits the top 5, and after a 60 second server cache refresh (the exploit waits 90 seconds), the homepage widget is loaded which triggers the plugin to download the payload from the server. The payload has a GIF header, and a double extension (.gif.php) allowing for arbitrary PHP code to be executed.

CVE-2021-42362