Wagtail vulnerable to denial-of-service via memory exhaustion when uploading large files

Wagtail is an open source content management system built on Django. Prior to versions 4.1.4 and 4.2.2, a memory exhaustion bug exists in Wagtail's handling of uploaded images and documents. For both images and documents, files are loaded into memory during upload for additional processing. A user with access to upload images or documents through the Wagtail admin interface could upload a file so large that it results in a crash of denial of service.

The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin. It can only be exploited by admin users with permission to upload images or documents.

Image uploads are restricted to 10MB by default, however this validation only happens on the frontend and on the backend after the vulnerable code.

Patched versions have been released as Wagtail 4.1.4 and Wagtail 4.2.2). Site owners who are unable to upgrade to the new versions are encouraged to add extra protections outside of Wagtail to limit the size of uploaded files.