Bit Form < 3.1.2 - Authenticated (Subscriber+) Arbitrary File Deletion via '_old' Parameter

Description

The Bit Form – Contact Form, Payment Forms, Multi Step Forms, Calculator & Custom Form Builder plugin for WordPress is vulnerable to arbitrary file deletion due to insufficient file path validation in the deleteFiles function in all versions up to, and including, 3.1.1 This makes it possible for authenticated attackers, with subscriber-level access and above, to delete arbitrary files on the server, which can easily lead to remote code execution when the right file is deleted (such as wp-config).