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[原创]第三题 影分身之术
2019-3-25 15:05 1294

[原创]第三题 影分身之术

2019-3-25 15:05
1294

第三题是一个dephi编写的程序,主要利用了WebBrowser控件,将密码藏在js代码中。拖入ida,观察到如下函数Tfrmcrackme_FormShow(int a1):
该函数是webbrowser主要内容,通过跟踪和调试,可以比较好的确定webbrowser的代码如下:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta charset="utf-8">
<title></title>
<script>
function sptWBCallback(spt_wb_id,spt_wb_name,optionstr){
    url='#sptWBCallback:id=';
    url=url+spt_wb_id+';eventName='+spt_wb_name;
    if(optionstr) 
    url=url+';params=optionstr';
    location=url;
}
function ckpswd() {    
    key="simpower91";    
    a = document.all.pswd.value;    
    if (a.indexOf(key) ==0) {        
    l=a.length;        
    i=key.length;        
    sptWBCallback(a.substring(i,l));    
    } 
    else {        
        alert("wrong!<" + a + "> is not my GUID ;-)");        
        return "1234";    
    }
}
function ok(){  
    alert("congratulations!");
}
</script>
</head>
<body>
<input value="" id="pswd" size=39></input>
<br><br><br>
<input type=button value="checkMyFlag" onclick="ckpswd();"></center> 
</body>
</html>

得出来key为simpower91,然后会触发sptWBCallback函数,函数会通过location=url复制进行url的变化,在delphi中,该操作是会触发onnavigator2回调函数的,在Tfrmcrackme_FormCreate(int a1)函数中的sub_491DCC函数中,有如下的函数,尝试对sub_492088()下断点,发现可以直接断下,判断该函数为js中location=url的回调函数。

int __fastcall sub_491DCC(int a1)
{
  int v1; // ebx
  int result; // eax

  v1 = a1;
  sub_491B78(a1);
  result = *(_DWORD *)(v1 + 64);
  *(_DWORD *)(result + 676) = v1;
  *(_DWORD *)(result + 672) = 0x00492088;
  return result;
}

跟踪该函数如下:

int __userpurge sptWBCallback@<eax>(int a1@<eax>, int a2@<edx>, int a3@<ecx>, int a4@<ebx>, int a5@<esi>, int edi0@<edi>, _WORD *a6, int a7, int a8, int a9, int a10, int a11)
{

  System::AnsiString = 0;
  v29 = 0;
  *(_DWORD *)input_url_str = 0;
  v27 = 0;
  v26 = 0;
  v25 = 0;
  v24 = a4;
  v23 = a5;
  v31 = a3;
  v32 = a2;
  v12 = a1;
  v22 = &savedregs;
  v21 = &loc_4921D1;
  v20 = __readfsdword(0);
  __writefsdword(0, (unsigned int)&v20);
  Variants::__linkproc__ VarToLStr(&v29, a11);
  v13 = sub_465C88((int)&str__sptWBCallback_[1], v29);
  if ( (signed int)v13 > 0 )
  {
    *a6 = -1;
    Variants::__linkproc__ VarToLStr(&System::AnsiString, a11);
    v14 = LStrLen(System::AnsiString);
    v15 = System::__linkproc__ LStrCopy(System::AnsiString, (int)(v13 + 15),v14 - (_DWORD)v13 - 14,(int)&System::AnsiString);
    LOBYTE(v15) = 1;
    LStrReplace(System::AnsiString, (int)&str___41[1], (int)&str____19[1], v12, edi0, (int)v13, (int)input_url_str, v15);
    System::__linkproc__ LStrLAsg(&System::AnsiString, *(_DWORD *)input_url_str);
    v16 = (Classes::TStrings *)TObject_Create((int)cls_Classes_TStringList, 1);
    (*(void (__fastcall **)(Classes::TStrings *, int))(*(_DWORD *)v16 + 44))(v16, System::AnsiString);// TStrings.SetTextStr
    if ( *(_WORD *)(v12 + 50) )
    {
      Classes::TStrings::GetValue(v16, (const int)&str_params[1]);
      v17 = v27;
      Classes::TStrings::GetValue(v16, (const int)&str_eventName[1]);
      v18 = v26;
      Classes::TStrings::GetValue(v16, (const int)&str_id[1]);
      (*(void (__fastcall **)(_DWORD, int, int, int))(v12 + 48))(*(_DWORD *)(v12 + 52), v25, v18, v17);
    }
  }
  if ( *(_WORD *)(v12 + 58) )
    (*(void (__fastcall **)(_DWORD, int, int, int, int, int, int, int, _WORD *))(v12 + 56))(
      *(_DWORD *)(v12 + 60),
      v32,
      v31,
      a11,
      a10,
      a9,
      a8,
      a7,
      a6);
  __writefsdword(0, v20);
  v22 = (int *)&loc_4921D8;
  return System::__linkproc__ LStrArrayClr(&v25, 6);
}

继续调试,进入到((void (__fastcall **)(_DWORD, int, int, int))(v12 + 48))((_DWORD *)(v12 + 52), v25, v18, v17)函数中,继续步进,发现如下函数:

CODE:0047394C sub_47394C      proc near               ; CODE XREF: _Tfrmcrackme_Button2Click+A1↓p
CODE:0047394C
CODE:0047394C var_2C          = dword ptr -2Ch
CODE:0047394C var_8           = dword ptr -8
CODE:0047394C var_4           = dword ptr -4
CODE:0047394C var_s0          = dword ptr  0
CODE:0047394C arg_4           = dword ptr  0Ch
CODE:0047394C
CODE:0047394C                 push    ebp
CODE:0047394D                 mov     ebp, esp
CODE:0047394F                 leave
CODE:00473950                 push    dword ptr [esp+0]
CODE:00473953                 push    [esp+var_s0]
CODE:00473956                 push    [esp+4+var_4]
CODE:00473959                 pusha
CODE:0047395A                 pushf
CODE:0047395B                 call    GetA400BaseAddr
CODE:00473960                 mov     ebx, eax
CODE:00473962                 xor     eax, eax
CODE:00473964                 mov     [ebx+1050h], eax
CODE:0047396A                 mov     eax, 0FFFFFFFFh
CODE:0047396F                 mov     [ebx+1054h], eax
CODE:00473975                 mov     [esp+2Ch+var_8], ebx
CODE:00473979                 add     [esp+2Ch+var_4], 5
CODE:0047397E                 mov     eax, [esp+2Ch+arg_4]
CODE:00473982                 mov     [esp+2Ch+var_s0], eax
CODE:00473986                 mov     eax, [ebx+1090h]
CODE:0047398C                 cmp     eax, 0
CODE:0047398F                 jnz     short loc_47399C
CODE:00473991                 mov     eax, offset sub_47378C
CODE:00473996                 mov     [ebx+1090h], eax
CODE:0047399C
CODE:0047399C loc_47399C:                             ; CODE XREF: sub_47394C+43↑j
CODE:0047399C                 popf
CODE:0047399D                 popa
CODE:0047399E                 call    sub_4734B0
CODE:004739A3                 pushf
CODE:004739A4                 pushf
CODE:004739A5                 pushf
CODE:004739A6                 pusha
CODE:004739A7                 pushf
CODE:004739A8                 jmp     short loc_4739CE
CODE:004739AA ; ---------------------------------------------------------------------------
CODE:004739AA
CODE:004739AA loc_4739AA:                             ; CODE XREF: sub_47394C+95↓j
CODE:004739AA                 mov     eax, [ebx+1058h]
CODE:004739B0                 mov     [esp+2Ch+var_s0], eax
CODE:004739B4                 mov     eax, [ebx+1050h]
CODE:004739BA                 mov     [esp+2Ch+var_4], eax
CODE:004739BE                 mov     [esp+2Ch+var_8], ebx
CODE:004739C2                 popf
CODE:004739C3                 popa
CODE:004739C4                 call    sub_4734B0
CODE:004739C9                 pushf
CODE:004739CA                 pushf
CODE:004739CB                 pushf
CODE:004739CC                 pusha
CODE:004739CD                 pushf
CODE:004739CE
CODE:004739CE loc_4739CE:                             ; CODE XREF: sub_47394C+5C↑j
CODE:004739CE                 call    GetA400BaseAddr
CODE:004739D3                 mov     ebx, eax
CODE:004739D5                 mov     eax, [ebx+1050h]
CODE:004739DB                 cmp     eax, [ebx+1054h]
CODE:004739E1                 jb      short loc_4739AA
CODE:004739E3                 mov     eax, [ebx+1050h]
CODE:004739E9                 mov     [esp+30h], eax
CODE:004739ED                 mov     eax, [esp+2Ch+var_2C]
CODE:004739F0                 mov     [esp+2Ch+var_s0], eax
CODE:004739F4                 popf
CODE:004739F5                 popa
CODE:004739F6                 add     esp, 8
CODE:004739F9                 popf
CODE:004739FA                 retn    8
CODE:004739FA sub_47394C      endp

这个还挺麻烦的,里面有很多的popa,pusha,popf等,所以慢慢跟踪到如下函数.

CODE:004734B0                 push    ebp
CODE:004734B1                 mov     ebp, esp
CODE:004734B3                 leave
CODE:004734B4                 pusha
CODE:004734B5                 pushf
CODE:004734B6                 push    ebp
CODE:004734B7                 mov     ebp, esp
CODE:004734B9                 sub     esp, 10h
CODE:004734BC                 lea     edx, [ebp+var_10]
CODE:004734BF                 push    edx
CODE:004734C0                 lea     edx, [ebp+var_C]
CODE:004734C3                 push    edx
CODE:004734C4                 lea     edx, [ebp+var_8]
CODE:004734C7                 push    edx
CODE:004734C8                 push    [ebp+arg_2C]
CODE:004734CB                 push    [ebp+arg_20]
CODE:004734CE                 push    [ebp+arg_28]
CODE:004734D1                 mov     edx, [ebp+arg_24]
CODE:004734D4                 mov     ecx, [ebp+4]
CODE:004734D7                 mov     [edx+105Ch], ecx
CODE:004734DD                 push    edx
CODE:004734DE                 call    sub_472EAC
CODE:004734E3                 leave
CODE:004734E4                 mov     eax, [esp+30h+var_30]
CODE:004734E7                 mov     [esp+30h+var_s0], eax
CODE:004734EB                 popf
CODE:004734EC                 popa
CODE:004734ED                 add     esp, 0Ch
CODE:004734F0                 popf
CODE:004734F1                 jmp     [esp-4+var_40]
CODE:004734F1 sub_4734B0      endp

函数利用了jmp [esp-4+var_40]该语句不停的跳转不同的指令进行对比,跟踪进去,发现这些指令就是用来比较flag的,单步跟踪和调试去满足它的比较条件,得出最后的flag为simpowera123。


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