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[原创]KCTF2022秋季赛 第八题 商贸往来 题解
发表于: 2022-12-3 20:16 13069

[原创]KCTF2022秋季赛 第八题 商贸往来 题解

mb_xxgcvcih 活跃值
2022-12-3 20:16
13069

开头包装的一层调用可以手动清理出来，他调用了sub_4026D2作为窗口回调，在WM_COMMAND里面

会再执行一次crackme，将入口点改为

0x401000通过调用Decompress函数，解压数据

类似格式是

在这里进行调用，v47用于加密，v45用于最后的验证

通过强制F5了几个函数发现，对应输入只进行了基于字节的异或加密、交换、查表，修改其中一个字节，只会对加密结果产生一个字节的影响。

这些代码花式调用了大量API，拖慢了计算速度，同时也有反调试。

其实根据附带的题目描述我感觉是叫你硬看，但我就偏要硬爆

将最后一个函数F5找到比对逻辑，将其导出。

将原始文件patch 入口点，push 0x402d4c call 0x401000 后 跟一个int3，然后nop掉0x04026C8的ExitProcess，到达int3后读取和重写flag的值，然后更改Eip为入口点进行下次爆破。

需要用到ScyllaHide，爆的时候执行一下InjectorCLIx86.exe sb.exe HookLibraryx86.dll nowait加载一下反反调试，配置文件选Themida x86/x64。

预计时间是(128 + 94) * 10 / 60 = 37分钟，

v21 = (*(int (__stdcall **)(int, int))(dword_4ABE44 + 92))(a1, 1001);// GetDlgItem
    if ( v21 )
    {
      for ( i = 0; i < 0x100; ++i )
        v7[i] = 0;
      v42 = (*(int (__stdcall **)(int))(v35 + 96))(v21);// GetWindowTextLengthA
      if ( v42 <= 210 && v42 >= 1 )
      {
        (*(void (__stdcall **)(int, char *, int))(v35 + 100))(v21, v7, 255);// GetWindowTextA
        v42 = (*(int (__stdcall **)(char *))(v35 + 24))(v7);// lstrlenA
        if ( v42 >= 1 && v42 <= 128 )
        {
          for ( j = v42; j < 128; ++j )
          {
            if ( j % 2 )
              v7[j] = 0x20;
            else
              v7[j] = 0x7F;
          }
          v34 = 1;
        }
        else
        {
          v34 = 0;
        }
      }
      else
      {
        v34 = 0;
      }
    }
    else
    {
      v34 = 0;
    }
    if ( v34 )
    {
      v43 = dword_4ABE44;
      if ( (*(int (__stdcall **)(_DWORD, char *, int))(dword_4ABE44 + 56))(0, v5, 255) )
      {
        strcpy(v27, "h");
        v27[2] = 0;
        v27[3] = 0;
        v27[4] = 0;
        v27[5] = 0xB8;
        v27[6] = 0;
        v27[7] = 0;
        v27[8] = 0;
        v27[9] = 0;
        v27[10] = 0xFF;
        v27[11] = 0xD0;
        Eax = 0;
        v31 = 0;
        v8[17] = 0xFFFFFFFF;
        for ( k = 0; k < 0x44; ++k )
          *((_BYTE *)v8 + k) = 0;
        v8[0] = 68;
        for ( m = 0; m < 0x10; ++m )
          *((_BYTE *)&v37 + m) = 0;
        if ( (*(int (__stdcall **)(char *, _DWORD, _DWORD, _DWORD, _DWORD, int, _DWORD, _DWORD, int *, int *))(v43 + 28))(// CreateProcessW
               v5,
               0,
               0,
               0,
               0,
               4,
               0,
               0,
               v8,
               &v37) )
        {
          v6.ContextFlags = 0x10007;
          if ( !(*(int (__stdcall **)(int, CONTEXT *))(v43 + 32))(v38, &v6) )// GetThreadContext
            goto LABEL_69;
          Eax = v6.Eax;
          v31 = (*(int (__stdcall **)(int, _DWORD, int, int, int))(v43 + 44))(v37, 0, 128, 4096, 4);
          if ( !v31 )
            goto LABEL_69;
          for ( n = 0; n < 0x80; n += v17 )
          {
            v17 = 0;
            if ( !(*(int (__stdcall **)(int, unsigned int, char *, unsigned int, int *))(v43
                                                                                       + 0x30))(// WriteProcessMemory
                    v37,
                    n + v31,
                    &v7[n],
                    128 - n,
                    &v17) )
            {
              v16 = 0;
              goto LABEL_45;
            }
          }
          v16 = 1;
          if ( !v16 )
            goto LABEL_69;
LABEL_45:
          v20 = (PIMAGE_DOS_HEADER)(*(int (__stdcall **)(_DWORD))(v43 + 20))(0);// GetModuleHandleW
          v10 = (int)v20 + v20->e_lfanew;
          v9 = Eax - *(_DWORD *)(v10 + 40);
          v11 = (char *)sub_401000 - (char *)v20;
          *(_DWORD *)&v27[1] = v31;
          *(_DWORD *)&v27[6] = (char *)sub_401000 - (char *)v20 + v9;
          for ( ii = 0; ii < 0xC; ii += v15 )
          {
            v15 = 0;
            if ( !(*(int (__stdcall **)(int, unsigned int, char *, unsigned int, int *))(v43 + 48))(
                    v37,
                    ii + Eax,
                    &v27[ii],
                    12 - ii,
                    &v15) )
            {
              v14 = 0;
              goto LABEL_52;
            }
          }
          v14 = 1;
LABEL_52:
          if ( v14 )
          {
            (*(void (__stdcall **)(int))(v43 + 36))(v38);// ResumeThread
            v30 = 2;
            if ( (*(int (__stdcall **)(int, int))(v43 + 60))(v37, 30000) )// WaitForSingleObject
            {
              (*(void (__stdcall **)(int, int))(v43 + 64))(v37, 2);// TerminateProcess
            }
            else
            {
              v18 = 0;
              if ( (*(int (__stdcall **)(int, int *))(v43 + 52))(v37, &v18) && v18 != 2 )// GetExitCodeProcess
                v30 = v18;
            }
v21 = (*(int (__stdcall **)(int, int))(dword_4ABE44 + 92))(a1, 1001);// GetDlgItem
    if ( v21 )
    {
      for ( i = 0; i < 0x100; ++i )
        v7[i] = 0;
      v42 = (*(int (__stdcall **)(int))(v35 + 96))(v21);// GetWindowTextLengthA
      if ( v42 <= 210 && v42 >= 1 )
      {
        (*(void (__stdcall **)(int, char *, int))(v35 + 100))(v21, v7, 255);// GetWindowTextA
        v42 = (*(int (__stdcall **)(char *))(v35 + 24))(v7);// lstrlenA
        if ( v42 >= 1 && v42 <= 128 )
        {
          for ( j = v42; j < 128; ++j )
          {
            if ( j % 2 )
              v7[j] = 0x20;
            else
              v7[j] = 0x7F;
          }
          v34 = 1;
        }
        else
        {
          v34 = 0;
        }
      }
      else
      {
        v34 = 0;
      }
    }
    else
    {
      v34 = 0;
    }
    if ( v34 )
    {
      v43 = dword_4ABE44;
      if ( (*(int (__stdcall **)(_DWORD, char *, int))(dword_4ABE44 + 56))(0, v5, 255) )
      {
        strcpy(v27, "h");
        v27[2] = 0;
        v27[3] = 0;
        v27[4] = 0;
        v27[5] = 0xB8;
        v27[6] = 0;
        v27[7] = 0;
        v27[8] = 0;
        v27[9] = 0;
        v27[10] = 0xFF;
        v27[11] = 0xD0;
        Eax = 0;
        v31 = 0;
        v8[17] = 0xFFFFFFFF;
        for ( k = 0; k < 0x44; ++k )
          *((_BYTE *)v8 + k) = 0;
        v8[0] = 68;
        for ( m = 0; m < 0x10; ++m )
          *((_BYTE *)&v37 + m) = 0;
        if ( (*(int (__stdcall **)(char *, _DWORD, _DWORD, _DWORD, _DWORD, int, _DWORD, _DWORD, int *, int *))(v43 + 28))(// CreateProcessW
               v5,
               0,
               0,
               0,
               0,
               4,
               0,
               0,
               v8,
               &v37) )
        {
          v6.ContextFlags = 0x10007;
          if ( !(*(int (__stdcall **)(int, CONTEXT *))(v43 + 32))(v38, &v6) )// GetThreadContext
            goto LABEL_69;
          Eax = v6.Eax;
          v31 = (*(int (__stdcall **)(int, _DWORD, int, int, int))(v43 + 44))(v37, 0, 128, 4096, 4);
          if ( !v31 )
            goto LABEL_69;
          for ( n = 0; n < 0x80; n += v17 )
          {
            v17 = 0;
            if ( !(*(int (__stdcall **)(int, unsigned int, char *, unsigned int, int *))(v43
                                                                                       + 0x30))(// WriteProcessMemory
                    v37,
                    n + v31,
                    &v7[n],
                    128 - n,
                    &v17) )
            {
              v16 = 0;
              goto LABEL_45;
            }
          }
          v16 = 1;
          if ( !v16 )
            goto LABEL_69;
LABEL_45:
          v20 = (PIMAGE_DOS_HEADER)(*(int (__stdcall **)(_DWORD))(v43 + 20))(0);// GetModuleHandleW
          v10 = (int)v20 + v20->e_lfanew;
          v9 = Eax - *(_DWORD *)(v10 + 40);
          v11 = (char *)sub_401000 - (char *)v20;
          *(_DWORD *)&v27[1] = v31;
          *(_DWORD *)&v27[6] = (char *)sub_401000 - (char *)v20 + v9;
          for ( ii = 0; ii < 0xC; ii += v15 )
          {
            v15 = 0;
            if ( !(*(int (__stdcall **)(int, unsigned int, char *, unsigned int, int *))(v43 + 48))(
                    v37,
                    ii + Eax,
                    &v27[ii],
                    12 - ii,
                    &v15) )
            {
              v14 = 0;
              goto LABEL_52;
            }
          }
          v14 = 1;
LABEL_52:
          if ( v14 )
          {
            (*(void (__stdcall **)(int))(v43 + 36))(v38);// ResumeThread
            v30 = 2;
            if ( (*(int (__stdcall **)(int, int))(v43 + 60))(v37, 30000) )// WaitForSingleObject
            {
              (*(void (__stdcall **)(int, int))(v43 + 64))(v37, 2);// TerminateProcess
            }
            else
            {
              v18 = 0;
              if ( (*(int (__stdcall **)(int, int *))(v43 + 52))(v37, &v18) && v18 != 2 )// GetExitCodeProcess
                v30 = v18;
            }
push input
mov eax,0x401000
call eax
push input
mov eax,0x401000
call eax
 
struct CodeData{
    uint32_t CodeSize;
    uint8_t code[CodeSize];
};
struct CodeData{
    uint32_t CodeSize;
    uint8_t code[CodeSize];
};
if ( v38 )
  {
    v90 = 0;
    v29[0] = 5;
    v29[1] = 0;
    v29[2] = 4;
    v29[3] = 3;
    v29[4] = 2;
    v29[5] = 1;
    for ( ii = 0; ii < 6; ++ii )
    {
      v32 = v29[ii];
      v92 = 0;
      v47 = 0;
      for ( jj = 0; jj <= v32; ++jj )
      {
        v47 = (int (__stdcall *)(_DWORD, _DWORD, _DWORD, _DWORD))(v108[30] + v92 + 4);
        v46 = *(_DWORD *)(v108[30] + v92);
        v92 += v46 + 4;
      }
      v90 = v47;
      if ( !v47(*v108, v108[1], v108[2], a1) )
        goto LABEL_134;
    }
    v56 = 1;
    v91 = 0;
    v45 = 0;
    for ( kk = 0; kk <= 6; ++kk )
    {
      v45 = (int (__stdcall *)(_DWORD, _DWORD, _DWORD, _DWORD))(v108[30] + v91 + 4);
      v48 = *(_DWORD *)(v108[30] + v91);
      v91 += v48 + 4;
    }
    v90 = v45;
    if ( !v45(*v108, v108[1], v108[2], a1) )
      v56 = 0;
  }
if ( v38 )
  {
    v90 = 0;
    v29[0] = 5;
    v29[1] = 0;
    v29[2] = 4;
    v29[3] = 3;
    v29[4] = 2;
    v29[5] = 1;
    for ( ii = 0; ii < 6; ++ii )
    {
      v32 = v29[ii];
      v92 = 0;
      v47 = 0;
      for ( jj = 0; jj <= v32; ++jj )
      {
        v47 = (int (__stdcall *)(_DWORD, _DWORD, _DWORD, _DWORD))(v108[30] + v92 + 4);
        v46 = *(_DWORD *)(v108[30] + v92);
        v92 += v46 + 4;
      }
      v90 = v47;
      if ( !v47(*v108, v108[1], v108[2], a1) )
        goto LABEL_134;
    }
    v56 = 1;
    v91 = 0;
    v45 = 0;
    for ( kk = 0; kk <= 6; ++kk )
    {
      v45 = (int (__stdcall *)(_DWORD, _DWORD, _DWORD, _DWORD))(v108[30] + v91 + 4);

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最后于 2022-12-3 20:23 被mb_xxgcvcih编辑 ，原因：
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