Unrestricted file upload

A file upload filter bypass exists in Magento 2.1 prior to 2.1.18, Magento 2.2 prior to 2.2.9, Magento 2.3 prior to 2.3.2. This can be exploited by an authenticated user with admin privileges to edit configuration keys to remove file extension filters, potentially resulting in the malicious upload and execution of malicious files on the server.