A vulnerability in an upstream library means an authenticated attacker can abuse locale input to execute arbitrary commands from a file that has previously been uploaded using the file upload functionality in the post editor.
Fixed in 5.2.3, all 5.x sites should update as soon as possible.
Fixed in 4.48.2, all 4.x sites should update as soon as possible.
Patched versions of Ghost add validation to the locale input to prevent execution of arbitrary files. Updating Ghost is the quickest complete solution.
As a workaround, if for any reason you cannot update your Ghost instance, you can block the POST /ghost/api/admin/settings/
endpoint, which will also disable updating settings for your site.
If you have any questions or comments about this advisory: