This vulnerability is currently awaiting analysis.
In WordPress 4.9.7, plugins uploaded via the admin area are not verified as being ZIP files. This allows for PHP files to be uploaded. Once a PHP file is uploaded, the plugin extraction fails, but the PHP file remains in a predictable wp-content/uploads location, allowing for an attacker to then execute the file. This represents a security risk in limited scenarios where an attacker (who does have the required capabilities for plugin uploads) cannot simply place arbitrary PHP code into a valid plugin ZIP file and upload that plugin, because a machine's wp-content/plugins directory permissions were set up to block all new plugins.