Format string vulnerability in XM Easy Personal FTP Server 5.2.1 allows remote attackers to cause a denial of service (application crash) via format string specifiers in the USER command or certain other available or nonexistent commands. NOTE: It was later reported that 5.3.0 is also vulnerable.
https://exchange.xforce.ibmcloud.com/vulnerabilities/31140
http://www.vupen.com/english/advisories/2007/0786
http://www.securityfocus.com/bid/22747
http://downloads.securityfocus.com/vulnerabilities/exploits/22747.pl