PowerPress < 8.3.8 - Authenticated Arbitrary File Upload leading to RCE

The plugin did not verify some of the uploaded feed images (such as the ones from Podcast Artwork section), allowing high privilege accounts (admin+) being able to upload arbitrary files, such as php, leading to RCE.

PoC

https://drive.google.com/file/d/1fyf6blzeG3VX22BQX7hc1QJ20rCY5p43/view?usp=sharing - Save the below HTML code in an HTML file - Replace the to the correct one - Logon to the blog as admin, go to the Blubrry PowerPress Settings > Feeds and get the nonce from the source of the page (Look for "_wpnonce) and replace by it’s value in the saved code - Open the saved HTML file with the same browser used to login to the blog, and click on ‘Submit request’ - Then open /wp-content/uploads/powerpress/up.php in the browser