CVE-2026-63115
Dashboard / Vulnerabilities / CVE-2026-63115
Summary: ActivityPub Undo handler can unfollow or remove reposts on behalf of other accounts
Details: 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.
References: https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63115.json, https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc, https://nvd.nist.gov/vuln/detail/CVE-2026-63115, https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e, https://github.com/TryGhost/ActivityPub/pull/1929
Affected packages
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