[pyftpdlib] Improper input validation in pyftpdlib

The ftp_QUIT function in ftpserver.py in pyftpdlib before 0.5.0 allows remote authenticated users to cause a denial of service (file descriptor exhaustion and daemon outage) by sending a QUIT command during a disallowed data-transfer attempt.

References

• https://nvd.nist.gov/vuln/detail/CVE-2008-7264
• https://github.com/giampaolo/pyftpdlib/issues/71
• https://github.com/advisories/GHSA-8p2c-fghc-9hj4