What is CVE-2026-63115?

CVE-2026-63115 is a medium-severity vulnerability in Tryghost Activitypub, classified under Authentication Bypass by Spoofing. CVSS score: 5.3/10. Published 2026-10-30.

How severe is CVE-2026-63115?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Auth bypass in Tryghost Activitypub

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` 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.

Published 2026-10-30.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Tryghost Activitypub — versions >= 1.0.0, < 1.2.6

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-63115?: CVE-2026-63115 is a medium-severity vulnerability in Tryghost Activitypub, classified under Authentication Bypass by Spoofing. CVSS score: 5.3/10. Published 2026-10-30.
How severe is CVE-2026-63115?: Medium severity. CVSS v3 base score is 5.3 out of 10.