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[原创]迷失丛林 Writeup by or4nge
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发表于: 2021-11-17 02:07
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很容易定位到程序的输入
输入长度为32，需要通过 sub_4014A0, sub_401580 的验证
4014A0 较为简单，是个经典的hexstr转成char存到 4041F0 这个地址，最后的16是计算转换后的长度，所以输入就是 [0-9A-F]{32}
随后将输入的前八字节存入 404000 中，剩下的部分传参进 sub_401580
要想让该函数返回1，需要先通过一组if验证
看一下使用的变量，应该是对前八字节的输入进行的验证
结合动调发现大概就是根据404000数组，构成一个 <value, index> 的结构，两两存放到404420当中
分析了一下404000数组的作用和特征，发现这个数组应该是构成一个环状的结构（以当前数值作为索引寻找下一个数），猜测不能有重复的数字，否则可能会构成小循环之类的，用脚本验证了一下发现后面248个数字果然没有重复，于是将前八字节的取值可能锁定到了 0x1e, 0x28, 0x4b, 0x6d, 0x8c, 0xa3, 0xd2, 0xfb 中，总共有 $8!=40320$ 种可能，完全可以爆破
把ida代码复制下来改一改
转换一下得到前八字节 B4D682C8BF2DE13A
确定前八字节后，只需要关注和参数（后八字节）有关的部分了，中间全部动调跳过
这一部分程序相较来说就简单了不少，主要是根据404000开头的八个字节作为初始值，每个字节单独与输入的八个字节进行运算，根据末尾bit决定是+1还是找索引，最终目的是凑成 GoodJob~ 这个字符串（sub_4024C0 是个字符串比较）
可以使用搜索算法求解，但考虑到每个字节是单独运算的，常规爆破也只需要 0x800 的运算量，所以还是直接爆破了
最后得到下半段验证码 D9B6AEF24A80CB22
if ( v21 == (char)169 && v22 == (char)0xAC && v23 == (char)0xA7 && v24 > 0xC8u)
if ( v21 == (char)169 && v22 == (char)0xAC && v23 == (char)0xA7 && v24 > 0xC8u)
#include <stdio.h>#include <stdint.h>#include <algorithm>#include <cstring>unsigned char byte_404000[] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xA2, 0x9B,
0xF4, 0xDF, 0xAC, 0x7C, 0xA1, 0xC6, 0x16, 0xD0, 0x0F, 0xDD,
0xDC, 0x73, 0xC5, 0x6B, 0xD1, 0x96, 0x47, 0xC2, 0x26, 0x67,
0x4E, 0x41, 0x82, 0x20, 0x56, 0x9A, 0x6E, 0x33, 0x92, 0x88,
0x29, 0xB5, 0xB4, 0x71, 0xA9, 0xCE, 0xC3, 0x34, 0x50, 0x59,
0xBF, 0x2D, 0x57, 0x22, 0xA6, 0x30, 0x04, 0xB2, 0xCD, 0x36,
0xD5, 0x68, 0x4D, 0x5B, 0x45, 0x9E, 0x85, 0xCF, 0x9D, 0xCC,
0x61, 0x78, 0x32, 0x76, 0x31, 0xE3, 0x80, 0xAD, 0x39, 0x4F,
0xFA, 0x72, 0x83, 0x4C, 0x86, 0x60, 0xB7, 0xD7, 0x63, 0x0C,
0x44, 0x35, 0xB3, 0x7B, 0x19, 0xD4, 0x69, 0x08, 0x0B, 0x1F,
0x3D, 0x11, 0x79, 0xD3, 0xEE, 0x93, 0x42, 0xDE, 0x23, 0x3B,
0x5D, 0x8D, 0xA5, 0x77, 0x5F, 0x58, 0xDB, 0x97, 0xF6, 0x7A,
0x18, 0x52, 0x15, 0x74, 0x25, 0x62, 0x2C, 0x05, 0xE8, 0x0D,
0x98, 0x2A, 0x43, 0xE2, 0xEF, 0x48, 0x87, 0x49, 0x1C, 0xCA,
0x2B, 0xA7, 0x8A, 0x09, 0x81, 0xE7, 0x53, 0xAA, 0xFF, 0x6F,
0x8E, 0x91, 0xF1, 0xF0, 0xA4, 0x46, 0x3A, 0x7D, 0x54, 0xEB,
0x2F, 0xC1, 0xC0, 0x0E, 0xBD, 0xE1, 0x6C, 0x64, 0xBE, 0xE4,
0x02, 0x3C, 0x5A, 0xA8, 0x9F, 0x37, 0xAF, 0xA0, 0x13, 0xED,
0x1B, 0xEC, 0x8B, 0x3E, 0x7E, 0x27, 0x99, 0x75, 0xAB, 0xFE,
0xD9, 0x3F, 0xF3, 0xEA, 0x70, 0xF7, 0x95, 0xBA, 0x1D, 0x40,
0xB0, 0xF9, 0xE5, 0xF8, 0x06, 0xBC, 0xB6, 0x03, 0xC9, 0x10,
0x9C, 0x2E, 0x89, 0x5C, 0x7F, 0xB1, 0x1A, 0xD6, 0x90, 0xAE,
0xDA, 0xE6, 0x5E, 0xB9, 0x84, 0xE9, 0x55, 0xBB, 0xC7, 0x0A,
0xE0, 0x66, 0xF2, 0xD8, 0xCB, 0x00, 0x12, 0xB8, 0x17, 0x94,
0x6A, 0x4A, 0x01, 0x24, 0x14, 0x51, 0x07, 0x65, 0x21, 0xC8,
0x38, 0xFD, 0x8F, 0xC4, 0xF5, 0xFC
};unsigned char byte_404220[520];
unsigned char byte_404420[65537];
int dword_404100[] = {2, 4, 8, 0x10, 0x20, 0x40, 0x80, 0};
using namespace std;int sub_401580(unsigned char *a2) {
int v2; // ebp
unsigned char *v3; // eax
int *v4; // esi
unsigned char *v5; // ecx
int v6; // edi
unsigned char *v7; // ecx
int v8; // edx
unsigned char *v9; // eax
int v10; // ecx
int v11; // esi
int v12; // eax
unsigned char v13; // dl
int v14; // edi
int v15; // eax
int v16; // ecx
int v17; // esi
int i; // eax
char v19; // dl
unsigned char v21; // [esp+10h] [ebp-Ch]
unsigned char v22; // [esp+11h] [ebp-Bh]
unsigned char v23; // [esp+12h] [ebp-Ah]
unsigned char v24; // [esp+13h] [ebp-9h]
unsigned char *v25; // [esp+14h] [ebp-8h]
v21 = 0;
v22 = 0;
v23 = 0;
v24 = 0;
v2 = 1;
v25 = byte_404420;
for (i = 0; i < 8; i++)
byte_404000[i] = a2[i];
do
{
byte_404220[0] = byte_404000[v2 - 1];
byte_404220[1] = v2;
v3 = byte_404220;
v4 = dword_404100;
v5 = &byte_404220[dword_404100[0]];
do
{
v6 = *v4; // 2, 4, 8, 10h, 20h, 40h, 80h
if ( *v4 > 0 )
{
do
{
v7 = v5 + 1;
*(v7 - 1) = byte_404000[*v3];
*v7 = *v3 + 1;
v5 = v7 + 1;
++v3;
--v6;
}
while ( v6 );
}
++v4;
}
while ( v4 < &(dword_404100[7]) );
v8 = 256;
do
{
++v25[*v3++];
--v8;
}
while ( v8 );
++v2;
v25 += 256;
}
while ( v2 - 1 < 256 );
v9 = &byte_404420[0x28];
v10 = 256;
do
{
if ( *(v9 - 40) )
++v21;
if ( *(v9 - 26) )
++v22;
if ( *v9 )
++v23;
if ( v9[39] )
++v24;
v9 += 256;
--v10;
}
while ( v10 );
if ( v21 == 0xA9 && v22 == 0xAC && v23 == 0xA7 && v24 > 0xC8u ){
for (i = 0; i < 8; i++){
printf("%hhX", a2[i]);
}
}
return 0;
}int main(){
unsigned char flag[] = {0x1e, 0x28, 0x4b, 0x6d, 0x8c, 0xa3, 0xd2, 0xfb};
do{
memset(byte_404420, 0, 65536);
sub_401580(flag);
}while (next_permutation(flag, flag + 8));
return 0;
}#include <stdio.h>#include <stdint.h>#include <algorithm>#include <cstring>unsigned char byte_404000[] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xA2, 0x9B,
0xF4, 0xDF, 0xAC, 0x7C, 0xA1, 0xC6, 0x16, 0xD0, 0x0F, 0xDD,
0xDC, 0x73, 0xC5, 0x6B, 0xD1, 0x96, 0x47, 0xC2, 0x26, 0x67,
0x4E, 0x41, 0x82, 0x20, 0x56, 0x9A, 0x6E, 0x33, 0x92, 0x88,
0x29, 0xB5, 0xB4, 0x71, 0xA9, 0xCE, 0xC3, 0x34, 0x50, 0x59,
0xBF, 0x2D, 0x57, 0x22, 0xA6, 0x30, 0x04, 0xB2, 0xCD, 0x36,
0xD5, 0x68, 0x4D, 0x5B, 0x45, 0x9E, 0x85, 0xCF, 0x9D, 0xCC,
0x61, 0x78, 0x32, 0x76, 0x31, 0xE3, 0x80, 0xAD, 0x39, 0x4F,
0xFA, 0x72, 0x83, 0x4C, 0x86, 0x60, 0xB7, 0xD7, 0x63, 0x0C,
0x44, 0x35, 0xB3, 0x7B, 0x19, 0xD4, 0x69, 0x08, 0x0B, 0x1F,
0x3D, 0x11, 0x79, 0xD3, 0xEE, 0x93, 0x42, 0xDE, 0x23, 0x3B,
0x5D, 0x8D, 0xA5, 0x77, 0x5F, 0x58, 0xDB, 0x97, 0xF6, 0x7A,
0x18, 0x52, 0x15, 0x74, 0x25, 0x62, 0x2C, 0x05, 0xE8, 0x0D,
0x98, 0x2A, 0x43, 0xE2, 0xEF, 0x48, 0x87, 0x49, 0x1C, 0xCA,
0x2B, 0xA7, 0x8A, 0x09, 0x81, 0xE7, 0x53, 0xAA, 0xFF, 0x6F,
0x8E, 0x91, 0xF1, 0xF0, 0xA4, 0x46, 0x3A, 0x7D, 0x54, 0xEB,
0x2F, 0xC1, 0xC0, 0x0E, 0xBD, 0xE1, 0x6C, 0x64, 0xBE, 0xE4,
0x02, 0x3C, 0x5A, 0xA8, 0x9F, 0x37, 0xAF, 0xA0, 0x13, 0xED,
0x1B, 0xEC, 0x8B, 0x3E, 0x7E, 0x27, 0x99, 0x75, 0xAB, 0xFE,
0xD9, 0x3F, 0xF3, 0xEA, 0x70, 0xF7, 0x95, 0xBA, 0x1D, 0x40,
0xB0, 0xF9, 0xE5, 0xF8, 0x06, 0xBC, 0xB6, 0x03, 0xC9, 0x10,
0x9C, 0x2E, 0x89, 0x5C, 0x7F, 0xB1, 0x1A, 0xD6, 0x90, 0xAE,
0xDA, 0xE6, 0x5E, 0xB9, 0x84, 0xE9, 0x55, 0xBB, 0xC7, 0x0A,
0xE0, 0x66, 0xF2, 0xD8, 0xCB, 0x00, 0x12, 0xB8, 0x17, 0x94,
0x6A, 0x4A, 0x01, 0x24, 0x14, 0x51, 0x07, 0x65, 0x21, 0xC8,
0x38, 0xFD, 0x8F, 0xC4, 0xF5, 0xFC
};unsigned char byte_404220[520];
unsigned char byte_404420[65537];
int dword_404100[] = {2, 4, 8, 0x10, 0x20, 0x40, 0x80, 0};
using namespace std;int sub_401580(unsigned char *a2) {
int v2; // ebp
unsigned char *v3; // eax
int *v4; // esi
unsigned char *v5; // ecx
int v6; // edi
unsigned char *v7; // ecx
int v8; // edx
unsigned char *v9; // eax
int v10; // ecx
int v11; // esi
int v12; // eax
unsigned char v13; // dl
int v14; // edi
int v15; // eax
int v16; // ecx
int v17; // esi
int i; // eax
char v19; // dl
unsigned char v21; // [esp+10h] [ebp-Ch]
unsigned char v22; // [esp+11h] [ebp-Bh]
unsigned char v23; // [esp+12h] [ebp-Ah]
unsigned char v24; // [esp+13h] [ebp-9h]
unsigned char *v25; // [esp+14h] [ebp-8h]
v21 = 0;
v22 = 0;
v23 = 0;
v24 = 0;
v2 = 1;
v25 = byte_404420;
for (i = 0; i < 8; i++)
byte_404000[i] = a2[i];
do
{
byte_404220[0] = byte_404000[v2 - 1];
byte_404220[1] = v2;
v3 = byte_404220;
v4 = dword_404100;
v5 = &byte_404220[dword_404100[0]];
do
{
v6 = *v4; // 2, 4, 8, 10h, 20h, 40h, 80h
if ( *v4 > 0 )
{
do
{
v7 = v5 + 1;
*(v7 - 1) = byte_404000[*v3];
*v7 = *v3 + 1;
v5 = v7 + 1;
++v3;
--v6;
}
while ( v6 );
}
++v4;
}
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