Date: 
Wednesday, Nov 18th, 2020
Security risk: 
Critical
Advisory ID: 
BACKDROP-SA-CORE-2020-007
Vulnerability: 
Remote Code Execution
Versions affected: 
  • Backdrop Core 1.17.x versions prior to 1.17.3
  • Backdrop Core 1.16.x versions prior to 1.16.5

Backdrop versions 1.15 and prior do not receive security coverage.

Description: 

Backdrop core does not properly sanitize certain filenames on uploaded files. This can lead to files being interpreted as the incorrect extension and served as the wrong MIME type, or executed as PHP for certain hosting configurations.

Solution: 

Upgrade your site to the most recent version of Backdrop core. Download available on the Backdrop CMS 1.17.3 release page. See the update instructions, if needed.

Additionally, it's recommended that you audit all previously uploaded files to check for malicious extensions. Look specifically for files that include more than one extension, like .php.txt or .html.gif.

Reported By: 
Fixed By: 

Security email list

Backdrop maintains a security mailing list. Whenever a security release comes out, an email will be sent to everyone subscribed to that list, announcing the new release. Please follow the steps below to join the Security email list.

  • Log in to backdropcms.org
  • Edit your profile
  • Scroll down to the "Email notifications" section
  • Check the box labeled "Receive BackdropCMS.org security announcements for core and contrib projects"