Use of Externally-Controlled Format String
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.
CWE-134 - Use of Externally-Controlled Format String
The software uses a function that accepts a format string as an argument, but the format string originates from an external source.