This indicates a possible attempt to exploit a Buffer Overflow in Serv-U FTP.
The vulnerability is due to the application's failure to sanitize the arguments of the "SITE CHMOD" command. An attacker can exploit this to execute arbitrary code on vulnerable systems by sending a "SITE CHMOD" command with an overly long filename.
RhinoSoft Serv-U 188.8.131.52
RhinoSoft Serv-U 4.1
RhinoSoft Serv-U 184.108.40.206
RhinoSoft Serv-U 3.1
RhinoSoft Serv-U 3.0
System Compromise: Allows remote attackers to execute arbitrary code.
Upgrade to Serv-U FTP server 5.0 and later versions at: