The most effective way to resolve these issues is to migrate away from version 2.0.8 to a supported, secure version. 1. Upgrade to vsftpd 3.0+

Many online references incorrectly attribute the "smiley face" backdoor—where entering :) as a username opens a root shell on port 6200—to version 2.0.8. This exploit actually affected a compromised distribution of vsftpd 2.3.4 .

Modern versions include critical security enhancements like per-process memory limits and improved sandboxing. VulnHub/Stapler1.md at master - GitHub

Legacy versions are vulnerable to memory leaks and CPU exhaustion. For example, a memory leak can occur if the deny_file option is enabled, allowing an attacker to exhaust system memory. Additionally, crafted "glob" expressions in STAT commands can trigger high CPU consumption.