CVE Catalog

CVE-2026-63115

MediumCVSS 5.3
Published: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.14%

4th percentile - higher than 4% of all known CVEs

Summary

In ActivityPub for Ghost 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.

Risk Assessment

This can lead to unauthorized removal of social relationships, compromising data integrity and user trust, although no private data is exposed and content is not modified.

Recommendation

Update ActivityPub to version 1.2.6 or later; for self-hosted services, an updated image and redeployment are required.

Related vulnerabilities

Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS