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[原创]KCTF2023 第六题 至暗时刻
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发表于: 2023-9-14 11:23
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代码中有很多syscall，win11调试进不去，需要布置win10虚拟机调试，才能看到函数名
创建的第一个线程，每次调用RtlFillMemory拷贝1字节，跟踪发现拷贝的就是 unk_140008050 中的数据，而且看着像jmp指令： 
用IDA加载能识别为代码，但是有很多错误。需要x64dbg调试shellcode。
先内存断，再执行断。shellcode运行后会将所有17替换成00，重新拿到shellcode，IDA F5就能完美识别
然后就是反复调试，发现字符串分为3块：
3201382652D139C0E22132DF1BC2212EA0991650A229B36436823D0B13D51E6 //前缀，3位一个16进制数
input //必须是3的倍数，后续分析长度必须是180
677116575313142309154604431859253431473963507533496829080645035455771774602058076430276921790210013736267644383505517280 //后缀 2位一个10进制数
核心函数是2063B，要求input每3位，是一个十六进制
比如 input[0]="112"，0x112=274，十位*9+个位=67，要跟后缀[0]相等
十位和个位就确定了。
同时十位和个位要作为下标，充当数独的坐标。百位就是数独的内容。
数独一共是9*9个格子，其中前缀是21个数，input是60个数。所以先转换已有的21个数，更新到棋盘
再求解出答案：
编程反算数独下标，
.text:0000000140001324 FF 15 2E 4D 00 00 call cs:IsDebuggerPresent
.text:000000014000132A 85 C0 test eax, eax
.text:000000014000132C 74 05 jz short loc_140001333
.text:0000000140001324 FF 15 2E 4D 00 00 call cs:IsDebuggerPresent
.text:000000014000132A 85 C0 test eax, eax
.text:000000014000132C 74 05 jz short loc_140001333
.text:0000000140001324 FF 15 2E 4D 00 00 call cs:IsDebuggerPresent
.text:000000014000132A | 31C0 | xor eax,eax |
.text:000000014000132C | EB 05 | jmp blackclient_.140001333 |
.text:000000014000132E | E8 65FFFFFF | call blackclient_.140001298 |
.text:0000000140001324 FF 15 2E 4D 00 00 call cs:IsDebuggerPresent
.text:000000014000132A | 31C0 | xor eax,eax |
.text:000000014000132C | EB 05 | jmp blackclient_.140001333 |
.text:000000014000132E | E8 65FFFFFF | call blackclient_.140001298 |
.text:0000000140001484 FF 15 DE 4B 00 00 call cs:CheckRemoteDebuggerPresent
.text:000000014000148A 83 7D 38 00 cmp [rbp+pbDebuggerPresent], 0
.text:000000014000148E 0F 84 95 00 00 00 jz loc_140001529
.text:0000000140001494 B9 08 00 00 00 mov ecx, 8 ; Size
.text:0000000140001484 FF 15 DE 4B 00 00 call cs:CheckRemoteDebuggerPresent
.text:000000014000148A 83 7D 38 00 cmp [rbp+pbDebuggerPresent], 0
.text:000000014000148E 0F 84 95 00 00 00 jz loc_140001529
.text:0000000140001494 B9 08 00 00 00 mov ecx, 8 ; Size
fun_scanf((__int64)"%s", input_1, v64);
fun_decode(v15, v52, (__int64)"*s>0?", 5); // kctf
sub_1400026AC(&Src, v16, v52, v17, qword_140009A80);// kctf拼接到字符串前面
sub_140002BBA((__int64)v19, (__int64)&Source, 0i64, (__int64)&v69, Size);// NtAllocateVirtualMemory
sub_140002DA9((__int64)v19); // NtWriteVirtualMemory
fun_decode(v20, v58, (__int64)"!?>d*", 5); // kernel32.dll
fun_decode(v22, v55, (__int64)"?x)da", v21); // RtlFillMemory(地址，大小，值)
( (unsigned int)sub_140003529((__int64)&hThread) )// NtCreateThreadEx
strncpy((char *)&Str1, Source + 67, 3ui64);
if ( !strcmp((const char *)&Str1, "110") ) // 此时Str1=="110"
{
v43 = &unk_140006590;
}
else
{
if ( strcmp((const char *)&Str1, "120") ) // 不等于120，就退出
ExitProcess(0);
v43 = &unk_140006598;
}
fun_decode(&Dest, 3, (__int64)v43, 3);
fun_printf((__int64)&unk_14000659C, &Dest); // 这里肯定就是打印成功了
fun_scanf((__int64)"%s", input_1, v64);
fun_decode(v15, v52, (__int64)"*s>0?", 5); // kctf
sub_1400026AC(&Src, v16, v52, v17, qword_140009A80);// kctf拼接到字符串前面
sub_140002BBA((__int64)v19, (__int64)&Source, 0i64, (__int64)&v69, Size);// NtAllocateVirtualMemory
sub_140002DA9((__int64)v19); // NtWriteVirtualMemory
fun_decode(v20, v58, (__int64)"!?>d*", 5); // kernel32.dll
fun_decode(v22, v55, (__int64)"?x)da", v21); // RtlFillMemory(地址，大小，值)
( (unsigned int)sub_140003529((__int64)&hThread) )// NtCreateThreadEx
strncpy((char *)&Str1, Source + 67, 3ui64);
if ( !strcmp((const char *)&Str1, "110") ) // 此时Str1=="110"
{
v43 = &unk_140006590;
}
else
{
if ( strcmp((const char *)&Str1, "120") ) // 不等于120，就退出
ExitProcess(0);
v43 = &unk_140006598;
}
fun_decode(&Dest, 3, (__int64)v43, 3);
fun_printf((__int64)&unk_14000659C, &Dest); // 这里肯定就是打印成功了
__int64 sub_20217(){ __int64 (__fastcall *CreateToolhelp32Snapshot)(signed __int64, _QWORD); // rbx
__int64 (__fastcall *Process32First)(__int64, int *); // r13
void (__fastcall *CloseHandle)(__int64); // r15
__int64 (*GetCurrentProcessId)(void); // r12
__int64 process; // rdi
bool v5; // si
__int64 handle; // rax
__int64 v7; // r14
int v9; // eax
__int64 (__fastcall *Process32Next_1)(__int64, int *); // rbx
__int64 (__fastcall *OpenProcess_1)(signed __int64, _QWORD); // r13
__int64 address; // rbx
int v13; // eax
int *v14; // rdx
_BYTE *v15; // rbx
int *lpBuffer; // [rsp+48h] [rbp-2B0h]
int v17; // [rsp+58h] [rbp-2A0h]
__int64 v18; // [rsp+60h] [rbp-298h]
int v19; // [rsp+68h] [rbp-290h]
int v20; // [rsp+80h] [rbp-278h]
int v21; // [rsp+88h] [rbp-270h]
__int64 Process32Next; // [rsp+300h] [rbp+8h]
__int64 OpenProcess; // [rsp+308h] [rbp+10h]
__int64 (__fastcall *VirtualQueryEx)(__int64, __int64, int **, signed __int64); // [rsp+310h] [rbp+18h]
CreateToolhelp32Snapshot = (__int64 (__fastcall *)(signed __int64, _QWORD))sub_20563(0xF88DDF46);
OpenProcess = sub_20563(0xFD0B55A7);
VirtualQueryEx = (__int64 (__fastcall *)(__int64, __int64, int **, signed __int64))sub_20563(0x242E6FF);
Process32First = (__int64 (__fastcall *)(__int64, int *))sub_20563(0x3F347695);
Process32Next = sub_20563(-1813961927);
CloseHandle = (void (__fastcall *)(__int64))sub_20563(0x1CA655F1);
GetCurrentProcessId = (__int64 (*)(void))sub_20563(55981281);
process = 0i64;
v20 = 0x238;
v5 = 0;
handle = CreateToolhelp32Snapshot(2i64, 0i64);
v7 = handle;
if ( handle == -1 )
return 0xFFFFFFFFi64;
v9 = Process32First(handle, &v20);
Process32Next_1 = (__int64 (__fastcall *)(__int64, int *))Process32Next;
OpenProcess_1 = (__int64 (__fastcall *)(signed __int64, _QWORD))OpenProcess;
while ( v9 )
{
if ( v21 == (unsigned int)GetCurrentProcessId() )
{
process = OpenProcess_1(0x2000000i64, 0i64);
if ( process )
{
address = 0i64;
while ( 1 )
{
do
{
if ( !VirtualQueryEx(process, address, &lpBuffer, 48i64) )
{
Process32Next_1 = (__int64 (__fastcall *)(__int64, int *))Process32Next;
OpenProcess_1 = (__int64 (__fastcall *)(signed __int64, _QWORD))OpenProcess;
goto LABEL_20;
}
address = (__int64)lpBuffer + v18;
}
while ( v19 != 4096 || v17 != 64 );
v13 = GetCurrentProcessId();
v14 = lpBuffer;
if ( v21 == v13 )
v5 = sub_2062F(*lpBuffer);
if ( v5 )
break;
*(_BYTE *)v14 = 'm'; // 第一层判断，kctf头
*((_BYTE *)v14 + 1) = 'j';
*((_BYTE *)v14 + 2) = ')';
*((_BYTE *)v14 + 3) = 0;
*((_BYTE *)v14 + 67) = '1';
*((_BYTE *)v14 + 68) = '2';
*((_BYTE *)v14 + 69) = '0';
}
v15 = v14 + 1;
if ( sub_20AA3((__int64)(v14 + 1)) ) // 所有判断，都在这里呗 传入kctf后面的字符串
{
*(v15 - 4) = 'i'; // 正确答案！！！！！！
*(v15 - 3) = 'o';
*(v15 - 2) = ' ';
*(v15 - 1) = 0;
v15[63] = '1';
v15[64] = '1';
}
else
{
*(v15 - 4) = 'm';
*(v15 - 3) = 'j';
*(v15 - 2) = ')';
*(v15 - 1) = 0;
v15[63] = '1';
v15[64] = '2';
}
v15[65] = '0';
break;
}
}
LABEL_20: v9 = Process32Next_1(v7, &v20);
}
CloseHandle(v7);
return ((__int64 (__fastcall *)(__int64))CloseHandle)(process);
}__int64 sub_20217(){ __int64 (__fastcall *CreateToolhelp32Snapshot)(signed __int64, _QWORD); // rbx
__int64 (__fastcall *Process32First)(__int64, int *); // r13
void (__fastcall *CloseHandle)(__int64); // r15
__int64 (*GetCurrentProcessId)(void); // r12
__int64 process; // rdi
bool v5; // si
__int64 handle; // rax
__int64 v7; // r14
int v9; // eax
__int64 (__fastcall *Process32Next_1)(__int64, int *); // rbx
__int64 (__fastcall *OpenProcess_1)(signed __int64, _QWORD); // r13
__int64 address; // rbx
int v13; // eax
int *v14; // rdx
_BYTE *v15; // rbx
int *lpBuffer; // [rsp+48h] [rbp-2B0h]
int v17; // [rsp+58h] [rbp-2A0h]
__int64 v18; // [rsp+60h] [rbp-298h]
int v19; // [rsp+68h] [rbp-290h]
int v20; // [rsp+80h] [rbp-278h]
int v21; // [rsp+88h] [rbp-270h]
__int64 Process32Next; // [rsp+300h] [rbp+8h]
__int64 OpenProcess; // [rsp+308h] [rbp+10h]
__int64 (__fastcall *VirtualQueryEx)(__int64, __int64, int **, signed __int64); // [rsp+310h] [rbp+18h]
CreateToolhelp32Snapshot = (__int64 (__fastcall *)(signed __int64, _QWORD))sub_20563(0xF88DDF46);
OpenProcess = sub_20563(0xFD0B55A7);
VirtualQueryEx = (__int64 (__fastcall *)(__int64, __int64, int **, signed __int64))sub_20563(0x242E6FF);
Process32First = (__int64 (__fastcall *)(__int64, int *))sub_20563(0x3F347695);
Process32Next = sub_20563(-1813961927);
CloseHandle = (void (__fastcall *)(__int64))sub_20563(0x1CA655F1);
GetCurrentProcessId = (__int64 (*)(void))sub_20563(55981281);
process = 0i64;
v20 = 0x238;
v5 = 0;
handle = CreateToolhelp32Snapshot(2i64, 0i64);
v7 = handle;
if ( handle == -1 )
return 0xFFFFFFFFi64;
v9 = Process32First(handle, &v20);
Process32Next_1 = (__int64 (__fastcall *)(__int64, int *))Process32Next;
OpenProcess_1 = (__int64 (__fastcall *)(signed __int64, _QWORD))OpenProcess;
while ( v9 )
{
if ( v21 == (unsigned int)GetCurrentProcessId() )
{
process = OpenProcess_1(0x2000000i64, 0i64);
if ( process )
{
address = 0i64;
while ( 1 )
{
do
{
if ( !VirtualQueryEx(process, address, &lpBuffer, 48i64) )
{
Process32Next_1 = (__int64 (__fastcall *)(__int64, int *))Process32Next;
OpenProcess_1 = (__int64 (__fastcall *)(signed __int64, _QWORD))OpenProcess;
goto LABEL_20;
}
address = (__int64)lpBuffer + v18;
}
while ( v19 != 4096 || v17 != 64 );
v13 = GetCurrentProcessId();
v14 = lpBuffer;
if ( v21 == v13 )
v5 = sub_2062F(*lpBuffer);
if ( v5 )
break;
*(_BYTE *)v14 = 'm'; // 第一层判断，kctf头
*((_BYTE *)v14 + 1) = 'j';
*((_BYTE *)v14 + 2) = ')';
*((_BYTE *)v14 + 3) = 0;
[招生]科锐逆向工程师培训(2024年11月15日实地，远程教学同时开班, 第51期)
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