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.

CVSS v3 5.3 MEDIUM

5.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e
https://github.com/TryGhost/ActivityPub/pull/1929
https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6
https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc

Configurations

No configuration.

History

30 Oct 2026, 22:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-30 22:16

Updated : 2026-10-30 22:16

NVD link : CVE-2026-63115

Mitre link : CVE-2026-63115

CVE.ORG link : CVE-2026-63115

JSON object : View

Products Affected

No product.

CWE

CWE-290

Authentication Bypass by Spoofing

CWE-345

Insufficient Verification of Data Authenticity

CWE-863

Incorrect Authorization

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