CVE-2026-63115 - ActivityPub is a multi-tenant ActivityPub server for Ghost, built with Fedify. From 1.0.0 until 1.2.6, the `Undo` handle
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.
MEDIUM
Severity & confidence
Source severitymedium
Platform severitymedium
Confidencehigh
Exploitationunknown
CVSS5.3
Affected
Reporting sources (1)
NIST NVD - National Vulnerability Database
Timeline & provenance
Published2026-10-30T22:16:57
Last updated2026-11-02T22:16:35
Ingested2026-11-02T06:23:32
FreshnessNEAR-REAL-TIME
Threat typevulnerability
Recommended action
No recommended action published with this item - review the original source.
Next steps
- Identify affected systems in your environment.
- Apply the vendor patch or mitigation guidance.
- Review logs for indicators described in the advisory.
- Follow the affected vendor/product to track updates.
Confidence explanation
Reported by a government or cert-grade source (CISA, NCSC, NVD, ENISA, MSRC).
Source type: standards ยท Original: NIST NVD - National Vulnerability Database
