CVE-2026-63115: TryGhost ActivityPub: ActivityPub is a multi-tenant ActivityPub server for Ghost, built with Fedify

ActivityPub is a multi-tenant ActivityPub server for Ghost, built with Fedify. From 1.0.0 until 1.2.6, the Undo handler allows a remote federated server to cause the service to act on a follow or repost as though the activity came from a different account. This permits removal of an existing foll...