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Monospace Directus Headless CMS File Upload / Rule Bypass

Monospace Directus Headless CMS File Upload / Rule Bypass
Posted Apr 7, 2021
Authored by Moritz Friedmann, Oliver Boehlk | Site sec-consult.com

Monospace Directus Headless CMS versions prior to 8.8.2 suffers from .htaccess rule bypass and arbitrary file upload vulnerabilities.

tags | exploit, arbitrary, vulnerability, file upload
advisories | CVE-2021-29641
SHA-256 | 0a87fe85b52203eaf5e6bafacaf4a67e5b5538421123168457d798bfb86748dd

Monospace Directus Headless CMS File Upload / Rule Bypass

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SEC Consult Vulnerability Lab Security Advisory < 20210407-0 >
title: Arbitrary File Upload and Bypassing .htaccess Rules
product: Monospace Directus Headless CMS
vulnerable version: < v8.8.2
fixed version: v8.8.2, v9 is not affected because of different architecture
CVE number: CVE-2021-29641
impact: High
homepage: https://directus.io/
found: 2020-12-15
by: Oliver Boehlk (Atos Germany)
Moritz Friedmann (Atos Germany)
SEC Consult Vulnerability Lab

An integrated part of SEC Consult, an Atos company
Europe | Asia | North America



Vendor description:
"Directus Open-Source, Free & Unlimited. No Strings Attached.
Our premium software is available at no cost for commercial and personal use.
This self-hosted version is full-featured, with no artificial limitations."

Source: https://directus.io/open-source/

Business recommendation:
The vendor provides an updated version for v8 which fixes the security issue. It should
be installed immediately.

Note: Directus v8 has been deprecated/discontinued and is replaced by version 9,
which currently does not have a final release version yet. Updating to Directus v9
fixes this vulnerability as well because the NodeJS architecture replaces
and hence is not affected.

According to the vendor, the identified security issue only applies to v8
relying on the specific Apache-based config in the Docker image, using the local-storage
driver for uploads. The recommendation from the vendor is to use a connection to S3 for
such installations, install the patch v8.8.2 or upgrade to version 9.

Vulnerability overview/description:
1) Arbitrary File Upload and Bypassing .htaccess Rules (CVE-2021-29641)
Any low privileged user with file upload permissions can upload webshells
other malicious PHP files which can be found in /uploads/_/originals/.

If the server prevents the execution of PHP files in the upload directory
attacker can move the file into a subdirectory where he can upload a custom .htaccess
file to enable PHP execution again.

Server side command execution can be used to retrieve the Directus configuration
and database credentials to escalate in-app privileges, retrieve password
or move laterally in the network.

Proof of concept:
1) Arbitrary File Upload and Bypassing .htaccess Rules (CVE-2021-29641)
A PoC environment can be created using a docker-compose.yml file:

version: "3"

image: directus/directus:v8.8.1-apache
- 8080:80
DIRECTUS_INSTALL_TITLE: vulnerable directus server

image: mariadb
MYSQL_USER: directus

Optionally, Directus data folders can be mounted for persistent storage:
- ./data/config:/var/directus/config
- ./data/uploads:/var/directus/public/uploads

An .htaccess file can be placed in the uploads directory to prevent PHP execution:
<IfModule mod_php7.c>
php_flag engine off

Initial installation requires "install" to be called:
docker-compose up -d && docker-compose run app install

Login defined in docker-compose:

An attacker can upload a PHP file and open it at uploads/_/originals/[randomid].php.
If a .htaccess file is used, the code does not get executed and gets returned in plain text.

You can edit the item in Directus and change the Filename Disk to "test/file.php" (it doesn't
matter that there is no folder named test yet, Directus/Apache does you a
favor and creates it
for you).

Now you can access the file at /uploads/_/originals/test/file.php.
Even if you delete the file in Directus it remains on the server, and can
be accessed via the
above mentioned URL.

To get code execution the next step is to simply upload an own .htaccess file containing
<IfModule mod_php7.c>
php_flag engine on

And again change the Filename Disk to test/.htaccess.

Now calling /uploads/_/originals/test/file.php executes the PHP file.

Vulnerable / tested versions:
The following versions have been tested and found to be vulnerable. According to the vendor,
only the Apache-based docker image with the local-storage driver is affected and not the
Directus suite as a whole.

* v8.4.0
* v8.8.1 (latest version at the time of the test)

It is assumed that all previous v8 versions are affected as well.

Version 9 uses a different architecture and is not affected by this vulnerability.

Vendor contact timeline:
2020-12-16 | Contacting vendor through security@directus.io; no reply
2021-03-04 | Contacting vendor again through security@directus.io
2021-03-05 | Vendor reply, exchanged S/MIME certificates
2021-03-08 | Sending security advisory to vendor
2021-03-12 | Asking the vendor whether they received the advisory; no reply
2021-03-25 | Asking vendor again for status update
2021-03-25 | Vendor: v8 will be fixed in new version
2021-03-26 | Vendor: the issue has been fixed in v8.8.2 available at dockerhub
2021-04-07 | Coordinated release of security advisory

The vendor provides an updated version v8.8.2 at dockerhub which fixes the security

Alternatively, version 9 can be installed as well, which uses a different
and is not affected.


Advisory URL:


SEC Consult Vulnerability Lab

SEC Consult, an Atos company
Europe | Asia | North America

About SEC Consult Vulnerability Lab
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult, an
Atos company. It ensures the continued knowledge gain of SEC Consult in the
field of network and application security to stay ahead of the attacker. The
SEC Consult Vulnerability Lab supports high-quality penetration testing and
the evaluation of new offensive and defensive technologies for our customers.
Hence our customers obtain the most current information about vulnerabilities
and valid recommendation about the risk profile of new technologies.

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EOF O. Boehlk, M. Friedmann / @2021

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