If you are running an affected version, to the latest stable release of vsftpd. The backdoored version was only available for a few days in July 2011, but many older "vulnerable by design" virtual machines still use it for educational purposes.
The exploit you are likely referring to is for vsftpd version 2.3.4 vsftpd 208 exploit github link
: The backdoor was triggered by sending a username that contained the characters :) during an FTP login. If you are running an affected version, to
Pick one, or I can choose and write a short story now. vsftpd 208 exploit github link