The exploit you are likely referring to is for vsftpd version 2.3.4
The VSFTPD 2.3.4 backdoor is a landmark incident in the history of open-source security. It highlights the dangers of supply chain attacks and the importance of verifying the integrity of downloaded software. For defenders, it serves as a reminder to patch legacy systems immediately and monitor for unauthorized open ports. For ethical hackers, it remains one of the best examples of a logic-based backdoor. vsftpd 208 exploit github link
If you are running an affected version, upgrade immediately 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
The most common "exploit" searches for vsftpd on GitHub center around the following: PwnHouse/OSVDB-73573/README.md at master - GitHub Upgrade to a patched version : If you're running vsftpd 2
If the backdoor is present, the connection will hang, and a shell will open on port 6200. Remediation
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