{"id":"CVE-2026-63115","aliases":["EUVD-2026-114518","GHSA-mm4q-93gr-5mwc"],"status":"published","title":"ActivityPub Undo handler can unfollow or remove reposts on behalf of other accounts","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.","severity":{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00143,"percentile":0.03636,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-290","CWE-345","CWE-863"],"published":"2026-10-30T21:33:55Z","modified":"2026-11-04T02:31:00Z","products":[{"vendor":"tryghost","product":"activitypub"},{"vendor":"unknown","product":"activitypub"}],"references":[{"url":"https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc","tags":["x_refsource_CONFIRM","advisory"]},{"url":"https://github.com/TryGhost/ActivityPub/pull/1929","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6","tags":["x_refsource_MISC","web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63115.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63115","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-63115","title":"ActivityPub Undo handler can unfollow or remove reposts on behalf of other accounts","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.","status":"published","published":"2026-10-30T21:33:55.894Z","modified":"2026-11-02T18:09:53.602Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-290","CWE-345","CWE-863"],"updated_at":"2026-11-02T19:47:07.544208Z"}],"euvd":[{"id":"EUVD-2026-114518","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.","status":"published","published":"2026-10-30T21:33:55Z","modified":"2026-11-02T18:09:53Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"updated_at":"2026-11-03T05:08:39.228431Z"}],"nvd":[{"id":"CVE-2026-63115","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.","status":"published","published":"2026-10-30T22:16:57.963Z","modified":"2026-11-02T19:18:09.753Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-290","CWE-345","CWE-863"],"updated_at":"2026-11-03T00:02:42.364722Z"}],"osv":[{"id":"CVE-2026-63115","title":"ActivityPub Undo handler can unfollow or remove reposts on behalf of other accounts","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.","status":"published","published":"2026-10-30T21:33:55.894Z","modified":"2026-11-04T02:31:00.032285389Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"cwes":["CWE-290","CWE-345","CWE-863"],"updated_at":"2026-11-04T02:54:44.889498Z"}]}}