CTF对抗-关于爆破迷宫路径的一系列思考_游戏逆向|游戏安全|yxfzedu.com

前几天学长给了一道maze的题，动态调试过程可谓非常艰难(对我现在的水平而言)，于是学长提供了一种用subprocess的方法

程序分析

首先通过字符串定位到主函数那里，我们发现cmp那里其实是一个长度校验，判断路径的长度是不是为140

这里为判断路径方向

中间过程太复杂，我们直接跳到后面，我们发现他判断所处位置是不是为0，还有判断最后到达位置对不对的

经过分析我们并不知道迷宫在哪，因此我们才要尝试爆破的方法。

爆破处理

首先第一步，我们要把长度校验给patch掉

重点的patch在后面，我们为了一步一步进行爆破，我们要对每一步进行爆破
但是有一个问题，后面不管走不走对都会输出
我们可以先写一个简单的试验一下

import subprocess
printable=['w','s','a','d']
for i in range(len(printable)):
    sh=subprocess.Popen("./mapmap", shell=True, stdout=subprocess.PIPE, stdin=subprocess.PIPE)
    sh.stdin.write((printable[i]+'\n').encode())
    sh.stdin.flush()
    output ,_ =sh.communicate()
    print(output)

我们发现根本无法判断是不是走对了，这个时候我们再patch一下

把下面那个指向wrong的地址改为指向' what()'的地址
我们这个时候可以再看一下

发现有不一样的回显了，我们根据这个可以写一个脚本，但是这里有一个问题，它在程序里面每走一步不会把走过的给标记，所以我们得自己标记一下，由于没有写这个标记，导致脚本跑了好久也没跑出来。

Exp

import subprocess
 
def dfs(path, n, x_location, y_location, count, try_direction, visited_paths, coordinates):
    if n < count:
        for direction in try_direction:
            process = subprocess.Popen("./mapmap", shell=True, stdout=subprocess.PIPE, stdin=subprocess.PIPE)
            next_path = path + direction
            process.stdin.write((next_path + '\n').encode())
            process.stdin.flush()
            output, _ = process.communicate()
             
            if b'wrong\n' not in output:
                new_x_location, new_y_location = x_location, y_location
                if direction == 'd':
                    new_x_location += 1
                elif direction == 'a':
                    new_x_location -= 1
                elif direction == 'w':
                    new_y_location -= 1
                elif direction == 's':
                    new_y_location += 1
                if (new_x_location, new_y_location) not in coordinates:
                    print(path)
                    coordinates[(new_x_location, new_y_location)] = next_path
                    dfs(next_path, len(next_path), new_x_location, new_y_location, count, try_direction, visited_paths, coordinates)
    elif n == count:
            visited_paths.append(path)
            coordinates[(x_location, y_location)] = path
 
# DFS start
if __name__ == '__main__':
    start_path = ''
    try_direction = ['w', 'd', 's', 'a']
    count = 140
    visited_paths = []
    coordinates = {}
 
    x_location = 0
    y_location = 0
    coordinates[(x_location, y_location)] = start_path
    print("\nVisit paths:")
    dfs(start_path, len(start_path), x_location, y_location, count, try_direction, visited_paths, coordinates)
     
    print("\nFinal paths:")
    for path in visited_paths:
        process = subprocess.Popen("./mapmap", shell=True, stdout=subprocess.PIPE, stdin=subprocess.PIPE)
        process.stdin.write((path + '\n').encode())
        process.stdin.flush()
        output, _ = process.communicate()
        if b'flag{md5(your input)}\n' in output:
            print(path)