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我和expression的日与被日经典分析

by jno
2007-11-29
http://www.ph4nt0m.org

当你第一次用expression方式来xss时，你肯定傻眼了，不停弹框，没法关闭浏览器，最终你只能祭出任务管理器将进程结束。也许你其他TAB页正有填到一半尚未提交的表单，你就这样被expression给日了，心里非常郁闷，于是就要想办法干它。

很多人第一反应就是cookie，没错这是个好办法：
div style="width: expression(if(document.cookie.indexOf('xxxx')0){alert(1);document.cookie='xxxx=1;'+document.cookie;})">/div>
不过这样写有个问题，就是被攻击者浏览器只能执行一次你的alert，cookie的作用域大于一次页面执行，适合用来做跨页面的标识，而不是仅仅用来控制一个页面里的某段代码的执行次数，而且你测试起来也挺麻烦，弄得不好就要清cookie。

循着这个思路很自然就会想到在页面里设置标识，于是就有了第二种方法：
div style="width: expression(if(!window.xxx){alert(1);window.xxx=1;})">/div>
使用全局变量来做标识，使我的代码在这个页面级别只执行一次，这样是一个比较完美的办法，也是目前被使用的最多的办法。

但是到这里总还觉得不爽，虽然我的alert只被执行了一次，但是判断代码还是在被不停的执行，我们还是在被它日，只不过感觉不出来而已了，我们的目标是日它，办法就是执行完我们的代码后删除这条expression，翻阅MSDN你很快能找到合适的方法：

object.style.removeExpression(sPropertyName)

看起来很美，可是你把这个语句放进expression内部用它来删除expression自身却怎么也不能成功，该死的alert还是会一遍遍的弹出来。使用setTimeout延迟执行？失败；使用execScript在全局执行？失败；结合setTimeout和execScript在延迟在全局执行？还是失败；在body尾部append一个外部script来执行？失败；在body尾部append一个外部script并且setTimeout 延迟并且execScript全局执行？草，终于tmd成功了：
!------1.htm------>
html>
style>
body {
width: expression(eval(String.fromCharCode(0x61,0x6C,0x65,0x72,0x74,0x28,0x31,0x29,0x3B,0x69,0x66,0x28,0x64,0x6F,0x63,0x75,0x6D,0x65,0x6E,0x74,0x2E,0x62,0x6F,0x64,0x79,0x29,0x7B,0x76,0x61,0x72,0x20,0x73,0x3D,0x64,0x6F,0x63,0x75,0x6D,0x65,0x6E,0x74,0x2E,0x63,0x72,0x65,0x61,0x74,0x65,0x45,0x6C,0x65,0x6D,0x65,0x6E,0x74,0x28,0x22,0x73,0x63,0x72,0x69,0x70,0x74,0x22,0x29,0x3B,0x64,0x6F,0x63,0x75,0x6D,0x65,0x6E,0x74,0x2E,0x62,0x6F,0x64,0x79,0x2E,0x61,0x70,0x70,0x65,0x6E,0x64,0x43,0x68,0x69,0x6C,0x64,0x28,0x73,0x29,0x3B,0x73,0x2E,0x73,0x72,0x63,0x3D,0x22,0x31,0x2E,0x6A,0x73,0x22,0x3B,0x7D)));
/*alert(1);if(document.body){var s=document.createElement("script");document.body.appendChild(s);s.src="1.js";}*/
}
/style>
body>
/body>
/html>
//--------1.js---------//
setTimeout(function(){execScript("document.body.style.removeExpression(\"width\")");}, 0);
可是还有那么一点不完美，就是无论怎么样，最少也要执行两次，不过我爽了，总算把这个expression给日了。当然如果你是个完美主义者，可以用这个方法结合if(!window.xxx)法。

各位看官看到这里，可能已经严重怀疑我是被虐狂，这么多方法测试下来，我还不弹框框弹到崩溃？其实我并非浪得虚名，测之前早有准备，先厚者脸皮去幻影邮件列表跪求alert框框原理，没想到大家非常热情地给予帮助，最终zzzevazzz大侠最先找到实现API是MessageBoxIndirectW，从 win2k源代码中觅得。然后又花上半日工夫草成一个hook MessageBoxIndirectW的小工具，可惜又遇到个小问题至今没有解决，这个函数的参数是个MSGBOXPARAMS结构体：
typedef struct {
UINT cbSize;
HWND hwndOwner;
HINSTANCE hInstance;
LPCTSTR lpszText;
LPCTSTR lpszCaption;
DWORD dwStyle;
LPCTSTR lpszIcon;
DWORD_PTR dwContextHelpId;
MSGBOXCALLBACK lpfnMsgBoxCallback;
DWORD dwLanguageId;
} MSGBOXPARAMS, *PMSGBOXPARAMS;
我写了个小程序测试发现只要把hwndOwner和dwStyle都置为0，这个对跨框就不是模态的，父窗口点关闭也可以关闭程序，我hook的目的也在于此，可是在IE里具体测试的时候，发现即使对话框不是模态的，我点关闭IE按钮也没法关闭IE窗口，所以这个方法只针对有TAB页的IE7有意义，对话框非模态后，我可以切换到其他TAB页去并关闭弹框的TAB页，但是对于IE6来说不能点关闭就没有意义，于是我干脆也不修改什么参数了，直接把这个函数返回掉了，代码在最后附上。

至此，我和expression的恩怨总算可以告一段落，整个世界清静了。
/*
* FileName: IEAlertPatch.c
* Version: 1.0
* Contact: luoluonet@yahoo.cn
* P.S: Thanks zzzEVAzzz, he found out the API that alert uses.
*/
#include Windows.h>
#include Tlhelp32.h>
#include Imagehlp.h>

#pragma comment(lib, "advapi32.lib")

//
// function prototype
//
DWORD WINAPI GetProcessIdByName(LPCTSTR lpProcessName);
__inline HookProc();
BOOL WINAPI HookAlert(DWORD pId);
LPVOID GetSC(LPVOID lpProc, DWORD* dwLen, DWORD dwReserved);

//
// start of winmain
//
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPreInstance, LPSTR lpCmdLine, int nCmdShow)
{
DWORD pId;
OSVERSIONINFOEX osvi;
BOOL bRet;
TCHAR procName[] = TEXT("iexplore.exe");

ZeroMemory(osvi, sizeof(OSVERSIONINFOEX));
osvi.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX);

//
// Get system version
//
bRet = GetVersionEx((OSVERSIONINFO *)osvi);
if (! bRet)
{
osvi.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
bRet = GetVersionEx((OSVERSIONINFO *)osvi);
if (! bRet)
goto FreeAndExit;
}

// Verify if it is NT system
if (osvi.dwPlatformId == VER_PLATFORM_WIN32_NT)
{
pId = GetProcessIdByName(procName);
if (pId != 0)
HookAlert(pId);
}

FreeAndExit:
return 0;

}
//
// End of WinMain
//

//
// @Name: GetProcessIdByName
// @Author: luoluo
// @Time: 2005-04-17
// @Param: lpProcessName spacifies the ProcessName
// @Ret: if success, return the process id
// if failed, return 0
//
DWORD WINAPI GetProcessIdByName(LPCTSTR lpProcessName)
{
HANDLE hSnapshot;
DWORD dwRet = 0;
LPPROCESSENTRY32 pPe32;
BOOL bRet;

// Get all the processes in the snapshot
hSnapshot = CreateToolhelp32Snapshot(0x00000002, 0);
if (hSnapshot == INVALID_HANDLE_VALUE)
{
goto FreeAndExit;
}

pPe32 = (LPPROCESSENTRY32)malloc(sizeof(PROCESSENTRY32));
ZeroMemory(pPe32, sizeof(PROCESSENTRY32));
pPe32->dwSize = sizeof(PROCESSENTRY32);

// Get the first process
bRet = Process32First(hSnapshot, pPe32);
if (! bRet)
{
goto FreeAndExit;
}

if (stricmp(lpProcessName, pPe32->szExeFile) == 0)
{
dwRet = pPe32->th32ProcessID;
goto FreeAndExit;
}

// Travesal the left processes
while (TRUE)
{
bRet = Process32Next(hSnapshot, pPe32);
if (! bRet)
{
goto FreeAndExit;
}

if (stricmp(lpProcessName, pPe32->szExeFile) == 0)
{
dwRet = pPe32->th32ProcessID;
goto FreeAndExit;
}
}

FreeAndExit:
if (pPe32 != NULL) free(pPe32);
if (hSnapshot != NULL) CloseHandle(hSnapshot);

return dwRet;
}

__inline __declspec(naked) HookProc()
{
__asm
{
leave
retn 4
/*
push esi
mov esi, [ebp+8h]
mov dword ptr [esi+4h], 0h // modify the hwnd
mov dword ptr [esi+14h], 0h // modify the type
pop esi
*/
_emit 90h
_emit 90h
_emit 90h
_emit 90h
}
}

LPVOID GetSC(LPVOID lpProc, DWORD* dwLen, DWORD dwReserved)
{
LPVOID lpProc1 = NULL;
LPVOID lpSC = NULL;

__asm
{
push ebx
mov ebx, lpProc
dec ebx
_loop:
inc ebx
cmp dword ptr [ebx], 90909090h
jne _loop
mov lpProc1, ebx
pop ebx
}

*dwLen = (DWORD)lpProc1 - (DWORD)lpProc;
lpSC = malloc(*dwLen + dwReserved);
memset(lpSC, 0, *dwLen + dwReserved);
memcpy(lpSC, lpProc, *dwLen);
*dwLen += dwReserved;

return lpSC;
}

BOOL WINAPI HookAlert(DWORD pId)
{
HMODULE hModule = NULL;
DWORD dwMessageBoxIndirectW = 0;
HANDLE hProcess;
HANDLE hToken;
TOKEN_PRIVILEGES tkp;
BOOL bRet = FALSE;
BOOL bRetVal;
LPVOID lpCodeMemory;
MEMORY_BASIC_INFORMATION mbi;
SIZE_T szRet;
DWORD dwOldProtect;
DWORD dwJmpOffset = 0;
unsigned char szJmpCode[5] = {0};
unsigned char szOldCode[5] = {0};
LPVOID lpHookCode = NULL;
DWORD dwHookCodeLen = 0;

hModule = LoadLibrary("user32.dll");
dwMessageBoxIndirectW = (DWORD)GetProcAddress(hModule, "MessageBoxIndirectW");

lpHookCode = GetSC(HookProc, dwHookCodeLen, 10);
if (lpHookCode == NULL)
{
goto FreeAndExit;
}

// Open process token to ajust privileges
bRetVal = OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, hToken);

if (! bRetVal)
{
goto FreeAndExit;
}

// Get the LUID for debug privilege
bRetVal = LookupPrivilegeValue(NULL, SE_DEBUG_NAME, tkp.Privileges[0].Luid);

if (! bRetVal)
{
goto FreeAndExit;
}

tkp.PrivilegeCount = 1;
tkp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;

// Adjust token privileges
bRetVal = AdjustTokenPrivileges(hToken, FALSE, tkp, sizeof(tkp), (PTOKEN_PRIVILEGES)NULL, 0);
if (! bRetVal)
{
goto FreeAndExit;
}

// Open remote process
hProcess = OpenProcess(PROCESS_VM_OPERATION | PROCESS_VM_READ | PROCESS_VM_WRITE | PROCESS_QUERY_INFORMATION, FALSE, pId);
if (hProcess == NULL)
{
goto FreeAndExit;
}

// Read 5 byte from function to be hooked
bRetVal = ReadProcessMemory(hProcess, (LPCVOID)dwMessageBoxIndirectW, szOldCode, sizeof(szOldCode), NULL);
if (! bRetVal)
{
goto FreeAndExit;
}

// Allocate memory from remote process
lpCodeMemory = VirtualAllocEx(hProcess, NULL, dwHookCodeLen, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
if (lpCodeMemory == NULL)
{
goto FreeAndExit;
}

// Query the page information
ZeroMemory(mbi, sizeof(MEMORY_BASIC_INFORMATION));
szRet = VirtualQueryEx(hProcess, lpCodeMemory, mbi, sizeof(MEMORY_BASIC_INFORMATION));
if (szRet == 0)
{
goto FreeAndExit;
}

// Modify the page protection for write
bRetVal = VirtualProtectEx(hProcess, mbi.BaseAddress, mbi.RegionSize, PAGE_EXECUTE_READWRITE, mbi.Protect);
if (! bRetVal)
{
goto FreeAndExit;
}

// the function has been hooked
if (szOldCode[0] == ((unsigned char)'\xE9'))
{
dwJmpOffset = (*((int*)(szOldCode + 1))) + dwMessageBoxIndirectW + 5 - ((DWORD)lpCodeMemory) - dwHookCodeLen + 5;
memcpy(szOldCode + 1, (LPVOID)(dwJmpOffset), 4);
}

// debugger present and breakpoint here
if (szOldCode[0] == '\xCC')
{
goto FreeAndExit;
}

// copy the start code of funciton hooked to the end of hook code
memcpy((LPVOID)(((DWORD)lpHookCode) + dwHookCodeLen - 10), szOldCode, sizeof(szOldCode));

// code jmp back to function hooked
memset((LPVOID)(((DWORD)lpHookCode) + dwHookCodeLen - 5), '\xE9', 1);
dwJmpOffset = dwMessageBoxIndirectW - ((DWORD)lpCodeMemory) - dwHookCodeLen + 5;
memcpy((LPVOID)(((DWORD)lpHookCode) + dwHookCodeLen - 4), (LPVOID)(dwJmpOffset), 4);

// Write my code to remote process memory
bRetVal = WriteProcessMemory(hProcess, lpCodeMemory, lpHookCode, dwHookCodeLen, 0);
if (! bRetVal)
{
VirtualFreeEx(hProcess, lpCodeMemory, dwHookCodeLen, MEM_RELEASE);
goto FreeAndExit;
}

// Modify the page protection to protect
bRetVal = VirtualProtectEx(hProcess, mbi.BaseAddress, mbi.RegionSize, mbi.Protect, dwOldProtect);
if (! bRetVal)
{
goto FreeAndExit;
}

// hook code
szJmpCode[0] = '\xE9'; // jmp
dwJmpOffset = ((DWORD)lpCodeMemory) - dwMessageBoxIndirectW - 5;
memcpy(szJmpCode + 1, (LPVOID)(dwJmpOffset), 4);

// Query the page information
ZeroMemory(mbi, sizeof(MEMORY_BASIC_INFORMATION));
szRet = VirtualQueryEx(hProcess, (LPVOID)dwMessageBoxIndirectW, mbi, sizeof(MEMORY_BASIC_INFORMATION));
if (szRet == 0)
{
goto FreeAndExit;
}

// Modify the page protection for write
bRetVal = VirtualProtectEx(hProcess, mbi.BaseAddress, mbi.RegionSize, PAGE_EXECUTE_READWRITE, mbi.Protect);
if (! bRetVal)
{
goto FreeAndExit;
}

// Write hook code to the functon to be hooked
bRetVal = WriteProcessMemory(hProcess, (LPVOID)dwMessageBoxIndirectW, szJmpCode, sizeof(szJmpCode), 0);
if (! bRetVal)
{
goto FreeAndExit;
}

// Modify the page protection to protect
bRetVal = VirtualProtectEx(hProcess, mbi.BaseAddress, mbi.RegionSize, mbi.Protect, dwOldProtect);
if (! bRetVal)
{
goto FreeAndExit;
}

FreeAndExit:
if (hProcess != NULL)
{
CloseHandle(hProcess);
}
if (hToken != NULL)
{
CloseHandle(hToken);
}
if (lpHookCode != NULL)
{
free(lpHookCode);
lpHookCode = NULL;
}

return bRet;
}

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