{"id":"CVE-2026-54740","aliases":["EUVD-2026-62844","GHSA-xmpx-2j2f-c7g7"],"status":"published","title":"Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators","description":"Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-alpha.18, a lower-ranked remote moderator can remove a higher-ranked moderator by sending a signed ActivityPub Remove activity to the target instance. The local API uses LocalUser::is_higher_mod_or_admin_check to enforce moderator rank, but CollectionRemove::verify in crates/apub/activities/src/community/collection_remove.rs only calls verify_mod_action. CollectionRemove::receive dereferences self.object as an ApubPerson, creates a CommunityModeratorForm, and calls CommunityActions::leave without checking that the actor outranks the moderator identified by the object field. In communities with federated moderators, a junior moderator can therefore strip senior moderators from the community moderator list even though the local API rejects the same action. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.","severity":{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00427,"percentile":0.37426,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-862"],"published":"2026-08-19T20:14:29Z","modified":"2026-11-11T02:49:02Z","products":[{"vendor":"lemmynet","product":"lemmy"}],"references":[{"url":"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7","tags":["x_refsource_CONFIRM","exploit","advisory"]},{"url":"https://github.com/LemmyNet/lemmy/pull/6475","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/LemmyNet/lemmy/pull/6478","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/LemmyNet/lemmy/commit/d127e714a66f34f6b9c8ea15f20097ac907cdf28","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/LemmyNet/lemmy/commit/ede1d348344ca2027fd1bc6a0cab25575c0c3a4c","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/LemmyNet/lemmy/releases/tag/0.19.19","tags":["x_refsource_MISC","web"]},{"url":"https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.18","tags":["x_refsource_MISC","web"]},{"url":"https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19","tags":["x_refsource_MISC","web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54740.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54740","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-54740","title":"Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators","description":"Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-alpha.18, a lower-ranked remote moderator can remove a higher-ranked moderator by sending a signed ActivityPub Remove activity to the target instance. The local API uses LocalUser::is_higher_mod_or_admin_check to enforce moderator rank, but CollectionRemove::verify in crates/apub/activities/src/community/collection_remove.rs only calls verify_mod_action. CollectionRemove::receive dereferences self.object as an ApubPerson, creates a CommunityModeratorForm, and calls CommunityActions::leave without checking that the actor outranks the moderator identified by the object field. In communities with federated moderators, a junior moderator can therefore strip senior moderators from the community moderator list even though the local API rejects the same action. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.","status":"published","published":"2026-08-19T20:14:29.391Z","modified":"2026-08-20T19:57:12.849Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-862"],"updated_at":"2026-11-02T13:38:09.774038Z"}],"euvd":[{"id":"EUVD-2026-62844","description":"Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-alpha.18, a lower-ranked remote moderator can remove a higher-ranked moderator by sending a signed ActivityPub Remove activity to the target instance. The local API uses LocalUser::is_higher_mod_or_admin_check to enforce moderator rank, but CollectionRemove::verify in crates/apub/activities/src/community/collection_remove.rs only calls verify_mod_action. CollectionRemove::receive dereferences self.object as an ApubPerson, creates a CommunityModeratorForm, and calls CommunityActions::leave without checking that the actor outranks the moderator identified by the object field. In communities with federated moderators, a junior moderator can therefore strip senior moderators from the community moderator list even though the local API rejects the same action. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.","status":"published","published":"2026-08-19T20:14:29Z","modified":"2026-08-20T19:57:12Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"updated_at":"2026-11-02T18:01:38.32409Z"}],"nvd":[{"id":"CVE-2026-54740","description":"Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-alpha.18, a lower-ranked remote moderator can remove a higher-ranked moderator by sending a signed ActivityPub Remove activity to the target instance. The local API uses LocalUser::is_higher_mod_or_admin_check to enforce moderator rank, but CollectionRemove::verify in crates/apub/activities/src/community/collection_remove.rs only calls verify_mod_action. CollectionRemove::receive dereferences self.object as an ApubPerson, creates a CommunityModeratorForm, and calls CommunityActions::leave without checking that the actor outranks the moderator identified by the object field. In communities with federated moderators, a junior moderator can therefore strip senior moderators from the community moderator list even though the local API rejects the same action. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.","status":"published","published":"2026-08-19T21:16:58.363Z","modified":"2026-09-09T21:15:59.613Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-862"],"updated_at":"2026-11-02T14:12:39.962615Z"}],"osv":[{"id":"CVE-2026-54740","title":"Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators","description":"Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-alpha.18, a lower-ranked remote moderator can remove a higher-ranked moderator by sending a signed ActivityPub Remove activity to the target instance. The local API uses LocalUser::is_higher_mod_or_admin_check to enforce moderator rank, but CollectionRemove::verify in crates/apub/activities/src/community/collection_remove.rs only calls verify_mod_action. CollectionRemove::receive dereferences self.object as an ApubPerson, creates a CommunityModeratorForm, and calls CommunityActions::leave without checking that the actor outranks the moderator identified by the object field. In communities with federated moderators, a junior moderator can therefore strip senior moderators from the community moderator list even though the local API rejects the same action. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.","status":"published","published":"2026-08-19T20:14:29.391Z","modified":"2026-11-11T10:47:34.682946544Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"cwes":["CWE-862"],"updated_at":"2026-11-11T03:21:28.618498Z"}]}}