Drupal core – Moderately critical – Improper validation – SA-CORE-2026-009

Project: Drupal coreDate: 2026-June-17Security risk: Moderately critical 11 ∕ 25 AC:Complex/A:User/CI:Some/II:Some/E:Theoretical/TD:UncommonVulnerability: Improper validationAffected versions: <10.5.12 || >=10.6.0 <10.6.11 || >=11.2.0 <11.2.14 || >=11.3.0 <11.3.12 || 11.0.* || 11.1.*CVE IDs: CVE-2026-55808Description: The JSON:API and REST modules allow you to upload image files to image fields.
The validation rules check the file extension of the uploaded file but not the file MIME type. This may allow a malicious user to upload a file that is not an image.
Certain web-server configurations may serve the uploaded file with its actual MIME type rather than an image type. This may lead to cross-site scripting (XSS) or other unexpected behavior.Solution: Install the latest version:
Drupal 11

If you use Drupal 11.3.x, update to Drupal 11.3.12.
If you use Drupal 11.2.x, update to Drupal 11.2.14.

Drupal 10

If you use Drupal 10.6.x, update to Drupal 10.6.11.
If you use Drupal 10.5.x, update to Drupal 10.5.12.

Drupal 11.1.x, Drupal 11.0.x, Drupal 10.4.x, and below are end-of-life and do not receive security coverage. (Drupal 8 and Drupal 9 have both reached end-of-life.)Reported By: 
cantina_security
Fixed By: 
Björn Brala (bbrala)
Kim Pepper (kim.pepper)
Lee Rowlands (larowlan) of the Drupal Security Team
Coordinated By: 
Damien McKenna (damienmckenna) of the Drupal Security Team
Greg Knaddison (greggles) of the Drupal Security Team
Lee Rowlands (larowlan) of the Drupal Security Team
Dave Long (longwave) of the Drupal Security Team
Juraj Nemec (poker10) of the Drupal Security Team
Jess (xjm) of the Drupal Security TeamSecurity advisoriesRead More