Member account takeover

Summary

### Impact An error in the implementation of the member email change functionality allows unauthenticated users to change the email address of arbitrary member accounts to one they control by crafting a request to the relevant API endpoint, and validating the new address via magic link sent to the new email address. Ghost(Pro) has already been patched. Self-hosters are impacted if running Ghost a version between 3.18.0 and 4.15.0 with members functionality enabled. ### Patches Fixed in 4.15.1, all 4.x sites should upgrade as soon as possible. Fixed in 3.42.6, all 3.x sites should upgrade as soon as possible. ### Workarounds The patch in 4.15.1 and 3.42.6 adds a new authenticated endpoint for updating member email addresses. 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 /members/api/send-magic-link/` endpoint, which will also disable member login and signup for your site. ### For more information If you have any questions or comments about this advisory: * Email us at [[email protected]](mailto:[email protected])