This indicates a possible exploit of a buffer-overflow vulnerability in the Serv-U FTP software.
The vulnerability is due to the application's failure to sanitize timezone arguments of the MDTM FTP command. An attacker may exploit this and execute arbitrary code on the vulnerable system by sending MDTM FTP command with an overly long string.
RhinoSoft Serv-U 4.2
RhinoSoft Serv-U 4.1 .0.11
RhinoSoft Serv-U 4.1
RhinoSoft Serv-U 4.0 .0.4
RhinoSoft Serv-U 3.1
RhinoSoft Serv-U 3.0
Allows remote authenticated users to execute arbitrary code.
Upgrade to Serv-U FTP server 5.0 and later versions at http://www.serv-u.com/.