Description
NodeBB does not bind the claimed author of an inbound ActivityPub object to the authenticated remote actor. The inbound middleware verifies the HTTP-signature actor and checks the origin of object.id, but never validates that attributedTo corresponds to the sender. In the object mock, attributedTo is used directly as a uid, and actors.assert silently ignores numeric identifiers (filtering them out without re-deriving the uid), so a federated remote actor can set attributedTo to a bare numeric value such as 1 and have the resulting post or private message created with that local uid as author, including the administrator account. This lets a remote attacker forge posts and direct messages attributed to arbitrary local users. Requires the ActivityPub/federation feature to be enabled.
Problem types
Insufficient Verification of Data Authenticity
Authentication Bypass by Spoofing
Product status
4.13.2 (semver)
References
github.com/...b-activitypub-attributedto-local-uid-spoof-poc (Proof of Concept)
github.com/...B/NodeBB/blob/v4.13.2/src/activitypub/mocks.js (Affected source)
www.vulncheck.com/...dated-attributedto-mapped-to-local-user (VulnCheck Advisory: NodeBB - ActivityPub Author Spoofing via Unvalidated attributedTo Mapped to Local User)