{"id":"CVE-2026-63115","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-63115","generatedAt":"2026-10-31T02:43:31.885Z","title":"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.","description":"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":"2026-10-30T22:16:58.000Z","lastModified":"2026-10-30T22:16:58.000Z","status":"Received","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"3.1","score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"},"cwe":["CWE-290","CWE-345","CWE-863"],"affected":[],"epss":null,"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and no EPSS score yet. Track it; it rarely justifies an emergency change on its own."},"changes":[{"kind":"new","label":"New CVE","at":"2026-10-30T22:16:58.000Z","detail":{"score":"5.3","severity":"MEDIUM","publishedAt":"2026-10-30T22:16:57.963Z"},"summary":"New CVE, medium severity (CVSS 5.3)."}],"references":[{"url":"https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e","source":"security-advisories@github.com"},{"url":"https://github.com/TryGhost/ActivityPub/pull/1929","source":"security-advisories@github.com"},{"url":"https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6","source":"security-advisories@github.com"},{"url":"https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc","source":"security-advisories@github.com"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-63115","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}