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  
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."  
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   
the PHP API  
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  
DIRECTUS_AUTH_SECRETKEY: directusprivtest  
DIRECTUS_AUTH_PUBLICKEY: directuspubtest  
image: mariadb  
MYSQL_ROOT_PASSWORD: directusroot  
MYSQL_DATABASE: directus  
MYSQL_USER: directus  
MYSQL_PASSWORD: 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; no reply  
2021-03-04 | Contacting vendor again through  
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.  
Interested to work with the experts of SEC Consult?  
Send us your application  
Interested in improving your cyber security with the experts of SEC Consult?  
Contact our local offices  
Mail: research at sec-consult dot com  
EOF O. Boehlk, M. Friedmann / @2021