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[原创] 看雪 2025 KCTF 签到题 废材少年觉醒
发表于: 2025-8-15 13:20 87

[原创] 看雪 2025 KCTF 签到题 废材少年觉醒

2025-8-15 13:20
87

通过二进制里的字符串得知是rust程序

从入口点依次找到rust的主函数:
(sub_140001400 -> sub_140001010 -> sub_140001AF0 -> sub_140001620)

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__int64 __fastcall sub_140001620()
{
  __int64 v0; // rax
  char **v1; // rdx
  char *v2; // r9
  unsigned __int8 *v3; // rdx
  unsigned __int8 *v4; // r10
  char v5; // bl
  unsigned __int8 *v6; // rbx
  unsigned __int8 *v7; // rax
  unsigned int v8; // edi
  int v9; // edx
  int v10; // r14d
  int v11; // ebp
  unsigned int v12; // ebx
  char v13; // bl
  char *v14; // rdi
  unsigned int v15; // ebx
  char v16; // bp
  char v17; // r14
  int v18; // r14d
  int v19; // ebp
  unsigned int v20; // ebp
  __int64 result; // rax
  char **v22; // [rsp+28h] [rbp-B0h] BYREF
  __int64 v23; // [rsp+30h] [rbp-A8h]
  __int64 v24; // [rsp+38h] [rbp-A0h]
  __int128 v25; // [rsp+40h] [rbp-98h]
  __int64 v26; // [rsp+58h] [rbp-80h] BYREF
  LPVOID lpMem; // [rsp+60h] [rbp-78h]
  __int64 v28; // [rsp+68h] [rbp-70h]
  _QWORD v29[2]; // [rsp+70h] [rbp-68h] BYREF
  _QWORD v30[2]; // [rsp+80h] [rbp-58h] BYREF
 
  v22 = &off_1400A10A0;
  v23 = 1;
  v24 = 8;
  v25 = 0;
  sub_140031F30(&v22);
  v22 = &off_1400A10C8;
  v23 = 1;
  v24 = 8;
  v25 = 0;
  sub_140031F30(&v22);
  v26 = sub_14002FCF0();
  v0 = sub_14002FDA0((__int64)&v26);
  if ( v0 )
  {
    v22 = (char **)v0;
    sub_140087C50(
      (unsigned int)aCalledResultUn,
      43,
      (unsigned int)&v22,
      (unsigned int)&off_1400A1030,
      (__int64)&off_1400A10D8);
  }
  v26 = 0;
  lpMem = (LPVOID)1;
  v28 = 0;
  v29[0] = sub_14002E310();
  if ( (sub_14002E3A0(v29, &v26) & 1) != 0 )
  {
    v22 = v1;
    sub_140087C50(
      (unsigned int)aCalledResultUn,
      43,
      (unsigned int)&v22,
      (unsigned int)&off_1400A1030,
      (__int64)&off_1400A10F0);
  }
  v2 = (char *)lpMem + v28;
  if ( v28 )
  {
    v3 = 0;
    v4 = (unsigned __int8 *)lpMem;
    while ( 1 )
    {
      v6 = v4;
      v7 = v3;
      v8 = *v4;
      if ( (v8 & 0x80u) != 0 )
      {
        v9 = v8 & 0x1F;
        v10 = v4[1] & 0x3F;
        if ( (unsigned __int8)v8 <= 0xDFu )
        {
          v4 += 2;
          v8 = v10 | (v9 << 6);
        }
        else
        {
          v11 = (v10 << 6) | v4[2] & 0x3F;
          if ( (unsigned __int8)v8 < 0xF0u )
          {
            v4 += 3;
            v8 = (v9 << 12) | v11;
          }
          else
          {
            v4 += 4;
            v8 = ((v8 & 7) << 18) | (v11 << 6) | v6[3] & 0x3F;
          }
        }
      }
      else
      {
        ++v4;
      }
      v3 = &v7[v4 - v6];
      if ( v8 - 9 >= 5 && v8 != 32 )
      {
        if ( v8 < 0x80 )
          goto LABEL_27;
        v12 = v8 >> 8;
        if ( v8 >> 8 > 0x1F )
        {
          if ( v12 == 32 )
          {
            v5 = *((_BYTE *)off_1400A0AC0 + (unsigned __int8)v8) >> 1;
          }
          else
          {
            if ( v12 != 48 )
              goto LABEL_27;
            v5 = v8 == 12288;
          }
        }
        else if ( v12 )
        {
          if ( v12 != 22 )
            goto LABEL_27;
          v5 = v8 == 5760;
        }
        else
        {
          v5 = *((_BYTE *)off_1400A0AC0 + (unsigned __int8)v8);
        }
        if ( (v5 & 1) == 0 )
          goto LABEL_27;
      }
      if ( v4 == (unsigned __int8 *)v2 )
        goto LABEL_53;
    }
  }
  v7 = 0;
  v3 = 0;
  v4 = (unsigned __int8 *)lpMem;
LABEL_27:
  if ( v4 == (unsigned __int8 *)v2 )
  {
LABEL_52:
    if ( v28 )
      goto LABEL_54;
LABEL_53:
    v7 = 0;
    v3 = 0;
    goto LABEL_54;
  }
  while ( 1 )
  {
    v14 = v2;
    v15 = *(v2 - 1);
    if ( (v15 & 0x80000000) != 0 )
    {
      v16 = *(v2 - 2);
      if ( v16 >= -64 )
      {
        v2 -= 2;
        v19 = v16 & 0x1F;
      }
      else
      {
        v17 = *(v2 - 3);
        if ( v17 >= -64 )
        {
          v2 -= 3;
          v18 = v17 & 0xF;
        }
        else
        {
          v2 -= 4;
          v18 = ((*(v14 - 4) & 7) << 6) | v17 & 0x3F;
        }
        v19 = (v18 << 6) | v16 & 0x3F;
      }
      v15 = (v19 << 6) | v15 & 0x3F;
      if ( v15 - 9 < 5 )
        goto LABEL_31;
    }
    else
    {
      --v2;
      if ( v15 - 9 < 5 )
        goto LABEL_31;
    }
    if ( v15 == 32 )
      goto LABEL_31;
    if ( v15 < 0x80 )
      break;
    v20 = v15 >> 8;
    if ( v15 >> 8 <= 0x1F )
    {
      if ( v20 )
      {
        if ( v20 != 22 )
          break;
        v13 = v15 == 0x1680;
      }
      else
      {
        v13 = *((_BYTE *)off_1400A0AC0 + (unsigned __int8)v15);
      }
      goto LABEL_30;
    }
    if ( v20 == 32 )
    {
      v13 = *((_BYTE *)off_1400A0AC0 + (unsigned __int8)v15) >> 1;
      goto LABEL_30;
    }
    if ( v20 != 48 )
      break;
    v13 = v15 == 12288;
LABEL_30:
    if ( (v13 & 1) == 0 )
      break;
LABEL_31:
    if ( v4 == (unsigned __int8 *)v2 )
      goto LABEL_52;
  }
  v3 = (unsigned __int8 *)&v14[v3 - v4];
LABEL_54:
  v30[0] = (char *)lpMem + (_QWORD)v7;
  v30[1] = v3 - v7;
  if ( sub_140001560((_BYTE *)lpMem + (_QWORD)v7, v3 - v7) )
  {
    v29[0] = v30;
    v29[1] = sub_140001480;
    v22 = &off_1400A1140;
    v23 = 2;
    v24 = (__int64)v29;
    v25 = 1u;
  }
  else
  {
    v22 = &off_1400A1118;
    v23 = 1;
    v24 = 8;
    v25 = 0;
  }
  result = sub_140031F30(&v22);
  if ( v26 )
    return sub_140001B50(lpMem);
  return result;
}

末尾的 sub_140001560 的返回结果经过 if 判断,两个分支的 off_1400A1140 和 off_1400A1118 分别指向成功和失败

打开 sub_140001560 ,把 ascii 数字转换为字符,直接是flag的明文

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bool __fastcall sub_140001560(_BYTE *a1, __int64 a2)
{
  return a2 == 25
      && *a1 == 'f'
      && a1[1] == 'l'
      && a1[2] == 'a'
      && a1[3] == 'g'
      && a1[4] == '{'
      && a1[5] == 'k'
      && a1[6] == 'c'
      && a1[7] == 't'
      && a1[8] == 'f'
      && a1[9] == '_'
      && a1[10] == 't'
      && a1[11] == 'i'
      && a1[12] == 'm'
      && a1[13] == 'e'
      && a1[14] == '_'
      && a1[15] == 'l'
      && a1[16] == 'e'
      && a1[17] == 'a'
      && a1[18] == 'p'
      && a1[19] == '_'
      && a1[20] == '2'
      && a1[21] == '0'
      && a1[22] == '2'
      && a1[23] == '5'
      && a1[24] == '}';
}

最终flag:flag{kctf_time_leap_2025}


至于主函数的逻辑,AI直接识别出来是UTF-8字符处理,并给出结论其作用为去除输入前后的空白字符,对应到rust则是标准库str::trim的内联


[培训]Windows内核深度攻防:从Hook技术到Rootkit实战!

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