{"id":"CVE-2026-54740","state":"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.","publishedAt":"2026-08-19T20:14:29.391Z","updatedAt":"2026-08-20T19:57:12.849Z","severity":{"score":6.5,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["LemmyNet lemmy"],"affected":[{"vendor":"LemmyNet","product":"lemmy","versions":[{"version":"< 0.19.19","status":"affected"},{"version":">= 1.0.0-alpha.0, < 1.0.0-alpha.18","status":"affected"}]}],"references":["https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7","https://github.com/LemmyNet/lemmy/pull/6475","https://github.com/LemmyNet/lemmy/pull/6478","https://github.com/LemmyNet/lemmy/commit/d127e714a66f34f6b9c8ea15f20097ac907cdf28","https://github.com/LemmyNet/lemmy/commit/ede1d348344ca2027fd1bc6a0cab25575c0c3a4c","https://github.com/LemmyNet/lemmy/releases/tag/0.19.19","https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.18","https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19"],"weaknesses":["CWE-862"],"ingestedAt":"2026-10-29T20:12:24.861Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/54xxx/CVE-2026-54740.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-54740","state":"PUBLISHED","datePublished":"2026-08-19T20:14:29.391Z","dateUpdated":"2026-08-20T19:57:12.849Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-15T23:07:33.233Z"},"containers":{"cna":{"title":"Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"LemmyNet","product":"lemmy","versions":[{"version":"< 0.19.19","status":"affected"},{"version":">= 1.0.0-alpha.0, < 1.0.0-alpha.18","status":"affected"}]}],"references":[{"url":"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7","name":"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/LemmyNet/lemmy/pull/6475","name":"https://github.com/LemmyNet/lemmy/pull/6475","tags":["x_refsource_MISC"]},{"url":"https://github.com/LemmyNet/lemmy/pull/6478","name":"https://github.com/LemmyNet/lemmy/pull/6478","tags":["x_refsource_MISC"]},{"url":"https://github.com/LemmyNet/lemmy/commit/d127e714a66f34f6b9c8ea15f20097ac907cdf28","name":"https://github.com/LemmyNet/lemmy/commit/d127e714a66f34f6b9c8ea15f20097ac907cdf28","tags":["x_refsource_MISC"]},{"url":"https://github.com/LemmyNet/lemmy/commit/ede1d348344ca2027fd1bc6a0cab25575c0c3a4c","name":"https://github.com/LemmyNet/lemmy/commit/ede1d348344ca2027fd1bc6a0cab25575c0c3a4c","tags":["x_refsource_MISC"]},{"url":"https://github.com/LemmyNet/lemmy/releases/tag/0.19.19","name":"https://github.com/LemmyNet/lemmy/releases/tag/0.19.19","tags":["x_refsource_MISC"]},{"url":"https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.18","name":"https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.18","tags":["x_refsource_MISC"]},{"url":"https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19","name":"https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":6.5,"baseSeverity":"MEDIUM","confidentialityImpact":"NONE","integrityImpact":"HIGH","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-862","lang":"en","description":"CWE-862: Missing Authorization","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-19T20:14:29.391Z"},"source":{"advisory":"GHSA-xmpx-2j2f-c7g7","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-20T19:57:07.165095Z","id":"CVE-2026-54740","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-20T19:57:12.849Z"}}]}}}