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 `follow` relationship or `repost` belonging to another account without that account's involvement.
No private data is exposed and content is not modified; the affected relationships can be re-established. Services proxying to Ghost's hosted ActivityPub server have already been updated, while self-hosted services require an updated image and redeployment. This issue is fixed in version 1.2.6.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
None
No data leak
Integrity
Low
Partial data modification
Availability
None
No disruption
CVSS Vector v3.1
Weakness Type (CWE)
References 4
https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6…
security-advisories@github.com
https://github.com/TryGhost/ActivityPub/pull/1929
security-advisories@github.com
https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6
security-advisories@github.com
https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc
security-advisories@github.com