The ao_ccss_import AJAX call in Autoptimize Wordpress Plugin 2.7.6 does not ensure that the file provided is a legitimate Zip file, allowing high privilege users to upload arbitrary files, such as PHP, leading to remote command execution.
https://wpvulndb.com/vulnerabilities/10372
http://packetstormsecurity.com/files/160850/WordPress-Autoptimize-Shell-Upload.html