Arbitrary File Upload and Bypassing .htaccess Rules in Monospace Directus Headless CMS

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

12.15.2020

By

Oliver Boehlk (Atos Germany), Moritz Friedmann (Atos Germany) | SEC Consult Vulnerability Lab

Monospace Directus CMS Docker images using the Apache webserver with local storage suffer from a vulnerability allowing any authenticated user to upload arbitrary files and directories. This leaves Directus vulnerable to remote code execution and manipulation of webserver .htaccess rules in the default configuration.

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 the PHP API and hence is not affected.

According to the vendor, the identified security issue only applies to v8 installations 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 or other malicious PHP files which can be found in /uploads/_/originals/. If the server prevents the execution of PHP files in the upload directory the 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 hashes 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"

services:
  app:
    image: directus/directus:v8.8.1-apache
    ports:
      - 8080:80
    environment:
      DIRECTUS_INSTALL_TITLE: vulnerable directus server
      DIRECTUS_INSTALL_EMAIL: admin@ha.ck
      DIRECTUS_INSTALL_PASSWORD: admin1
      DIRECTUS_AUTH_SECRETKEY: directusprivtest
      DIRECTUS_AUTH_PUBLICKEY: directuspubtest
      DIRECTUS_DATABASE_HOST: db
      DIRECTUS_DATABASE_NAME: directus
      DIRECTUS_DATABASE_USERNAME: directus
      DIRECTUS_DATABASE_PASSWORD: directus

  db:
    image: mariadb
    environment:
      MYSQL_ROOT_PASSWORD: directusroot
      MYSQL_DATABASE: directus
      MYSQL_USER: directus
      MYSQL_PASSWORD: directus


Optionally, Directus data folders can be mounted for persistent storage:

volumes:
- ./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
</IfModule>

Initial installation requires "install" to be called:

docker-compose up -d && docker-compose run app install

Login defined in docker-compose:

admin@ha.ck:admin1

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
</IfModule>

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

Solution

The vendor provides an updated version v8.8.2 at dockerhub which fixes the security issue:
https://hub.docker.com/layers/directus/directus/v8.8.2-apache/images/sha256-d9898b6442b0150c3c377b50e706757f35d2d563bd82ddaf97f3ae4ba450a6e6?context=explore

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


Workaround

None


Advisory URL

https://sec-consult.com/vulnerability-lab/

 

EOF O. Boehlk, M. Friedmann / @2021