Autoptimize < 2.7.8 - Arbitrary File Upload via "Import Settings"

Regularly, zip which contained a PHP file was extracted, but the PHP extension was not on a white list so it was removed from the disk afterwards. It turned out that it is possible to upload a zip which contained a directory with PHP file in it and then it was not removed from the disk. 

Upload can be done using Import Settings functionality available in the following directory: http://localhost:8000/wp-content/uploads/ao_ccss/dir/wp-admin/options-general.php?page=ao_critcss 

Example content of an archive:
$ zip -sf rce.zip
Archive contains:
  dir/
  dir/index.php
  settings.json
Total 3 entries (20 bytes)

Example content of dir/index.php file:
<?php phpinfo() ?>

settings.json is an empty file.

As you can see, there is a "dir" directory inside a zip which contains index.php file. Both will not be removed from the disk after being extracted. After the upload, file can be accessed by visiting such address: http://localhost:8000/wp-content/uploads/ao_ccss/dir/ 

Due to the fact that file is named index.php, there was no need to include file name in the address.