Crob FTP Server 3.6.1 b.263 allows remote attackers to cause a denial of service via a long series of "?A" sequences in the (1) LIST and possibly (2) NLST command.
https://www.exploit-db.com/exploits/2926
https://exchange.xforce.ibmcloud.com/vulnerabilities/30867
https://euvd.enisa.europa.eu/vulnerability/EUVD-2006-6541
http://www.vupen.com/english/advisories/2006/4994