Core FTP 2.0 build 653 contains a denial of service vulnerability in the PBSZ command that allows unauthenticated attackers to crash the FTP server. The vulnerability is triggered when attackers send a PBSZ command with a payload exceeding 211 bytes, causing an access violation and crashing the server process. This is a buffer overflow vulnerability that does not require authentication to exploit. The vulnerability affects Core FTP Server version 2.0 build 653 specifically. Exploitation results in service disruption through process crashes.