{"id":"CVE-2026-63115","published":"2026-10-30T22:16:57.963","lastModified":"2026-10-30T22:16:57.963","description":"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.","cvssScore":5.3,"cvssSeverity":"MEDIUM","cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","cwes":["CWE-290","CWE-345","CWE-863"],"vendors":[],"products":[],"references":[{"url":"https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e","tags":[]},{"url":"https://github.com/TryGhost/ActivityPub/pull/1929","tags":[]},{"url":"https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6","tags":[]},{"url":"https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc","tags":[]}],"exploitRefs":[{"url":"https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e","tags":[]},{"url":"https://github.com/TryGhost/ActivityPub/pull/1929","tags":[]},{"url":"https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6","tags":[]},{"url":"https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc","tags":[]}],"hasPoc":true,"ai":null}