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WordPress wp-trackback.php漏洞分析
文/Superhei 2007/1/9
1.Stefan Esser大牛2007/01/05发布的WordPress Trackback Charset Decoding SQL Injection Vulnerability [1]

Code:wp-trackback.php

$tb_url = $_POST['url'];
$title = $_POST['title'];
$excerpt = $_POST['excerpt'];
$blog_name = $_POST['blog_name'];
$charset = $_POST['charset'];
…….
if ( function_exists('mb_convert_encoding') ) { // For international trackbacks
$title = mb_convert_encoding($title, get_settings('blog_charset'), $charset);
$excerpt = mb_convert_encoding($excerpt, get_settings('blog_charset'), $charset);
$blog_name = mb_convert_encoding($blog_name, get_settings('blog_charset'), $charset);
}
…….
$dupe = $wpdb->get_results("SELECT * FROM $wpdb->comments WHERE comment_post_ID = '$comment_post_ID' AND comment_author_url = '$comment_author_url'");

变量$charset编码post—>mb_convert_encoding()转换为get_settings('blog_charset') [utf-8]—->select

se大牛的exp[2] 是用的uf7编码：'==>+-ACc- 饶过gpc，然后通过mb_convert_encoding转化为utf-8 '<==+-ACc-

其实这个就是编码引起的2次攻击[3]饶过gpc引起的SqlInj。

官方发布的补丁：2.0.6 wp-trackback.php

// These three are stripslashed here so that they can be properly escaped after mb_convert_encoding()
$title = stripslashes($_POST['title']);
$excerpt = stripslashes($_POST['excerpt']);
$blog_name = stripslashes($_POST['blog_name']);
………
// Now that mb_convert_encoding() has been given a swing, we need to escape these three
$title = $wpdb->escape($title);
$excerpt = $wpdb->escape($excerpt);
$blog_name = $wpdb->escape($blog_name);

变量经过stripslashes()—>mb_convert_encoding()—>escape()—>select

我们看看escape() ：wp-includes\wp-db.php

function escape($string) {
return addslashes( $string ); // Disable rest for now, causing problems
if( !$this->dbh || version_compare( phpversion(), '4.3.0' ) == '-1' )
return mysql_escape_string( $string );
else
return mysql_real_escape_string( $string, $this->dbh );
}

mysql_real_escape_string()在一定的条件下是可以绕过的：
The addslashes() Versus mysql_real_escape_string() Debate http://shiflett.org/archive/184
村雨牛牛在xcon也说过，但是mysql支持gbk的情况还是比较少的。有兴趣的可以自己测试下 :)

2.rgod于2007/01/08发布的WordPress <= 2.0.6 wp-trackback.php Zend_Hash_Del_Key_Or_Index / sql injection exploit [4]

Code:wp-settings.php

function unregister_GLOBALS() {
if ( !ini_get('register_globals') )
return;

if ( isset($_REQUEST['GLOBALS']) )
die('GLOBALS overwrite attempt detected');

// Variables that shouldn't be unset
$noUnset = array('GLOBALS', '_GET', '_POST', '_COOKIE', '_REQUEST', '_SERVER', '_ENV', '_FILES', 'table_prefix');

$input = array_merge($_GET, $_POST, $_COOKIE, $_SERVER, $_ENV, $_FILES, isset($_SESSION) && is_array($_SESSION) ? $_SESSION : array());
foreach ( $input as $k => $v )
if ( !in_array($k, $noUnset) && isset($GLOBALS[$k]) )
unset($GLOBALS[$k]);
}

unregister_GLOBALS();

这里unset了$_GET, $_POST, $_COOKIE, $_SERVER, $_ENV, $_FILES, $_SESSION 等提交的变量。

Code:wp-trackback.php

if ( !intval( $tb_id ) ) //注意这个
trackback_response(1, 'I really need an ID for this to work.');

……………..

if ( !empty($tb_url) && !empty($title) && !empty($tb_url) ) {
header('Content-Type: text/xml; charset=' . get_option('blog_charset') );

$pingstatus = $wpdb->get_var("SELECT ping_status FROM $wpdb->posts WHERE ID = $tb_id");
……

$tb_id没有’ 通过unset后存在end_Hash_Del_Key_Or_Index漏洞，导致注射。在分析时候提交：tb_id='&1740009377=1&496546471=1
返回：I really need an ID for this to work 原来是在 ：
if ( !intval( $tb_id ) ) //这里拦住了。
trackback_response(1, 'I really need an ID for this to work.');

提交tb_id=1'&1740009377=1&496546471=1 成功触发，这里引发了一比较有意思的问题 ：
<?
//test.php
print intval($_REQUEST["id"]);
?>
提交test.php?id=a1 得到 0，提交test.php?id=12a 得到 12。
可以看出 intval是根据第1个字符来判断的，这样如果是像wp这样的判断：if ( !intval( $_ ) ) 还是有安全隐患的。

参考：
[1]：http://www.hardened-php.net/advisory_022007.141.html
[2]：http://www.milw0rm.com/exploits/3095
[3]：http://superhei.blogbus.com/files/1157120596.ppt
[4]：http://retrogod.altervista.org/wordpress_206_zhdkoi_sql.html