LemmyNet Lemmy up to 0.19.18/1.0.0-alpha.17 Moderator Rank Verification collection_remove.rs receive object privileges management

Summaryinfo

A vulnerability classified as problematic was found in LemmyNet Lemmy up to 0.19.18/1.0.0-alpha.17. Affected is the function CollectionRemove::receive of the file crates/apub/activities/src/community/collection_remove.rs of the component Moderator Rank Verification. The manipulation of the argument object results in privileges management. This vulnerability is cataloged as CVE-2026-54740. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in LemmyNet Lemmy up to 0.19.18/1.0.0-alpha.17. It has been classified as problematic. Affected is the function CollectionRemove::receive of the file crates/apub/activities/src/community/collection_remove.rs of the component Moderator Rank Verification. The manipulation of the argument object with an unknown input leads to a privileges management vulnerability. CWE is classifying the issue as CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. This is going to have an impact on integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-54740 since 06/16/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1068 by the MITRE ATT&CK project.

Upgrading to version 0.19.19 or 1.0.0-alpha.18 eliminates this vulnerability.

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Productinfo

Vendor

• LemmyNet

Name

• Lemmy

Version

• 0.19.0
• 0.19.1
• 0.19.2
• 0.19.3
• 0.19.4
• 0.19.5
• 0.19.6
• 0.19.7
• 0.19.8
• 0.19.9
• 0.19.10
• 0.19.11
• 0.19.12
• 0.19.13
• 0.19.14
• 0.19.15
• 0.19.16
• 0.19.17
• 0.19.18
• 1.0.0-alpha.0
• 1.0.0-alpha.1
• 1.0.0-alpha.2
• 1.0.0-alpha.3
• 1.0.0-alpha.4
• 1.0.0-alpha.5
• 1.0.0-alpha.6
• 1.0.0-alpha.7
• 1.0.0-alpha.8
• 1.0.0-alpha.9
• 1.0.0-alpha.10
• 1.0.0-alpha.11
• 1.0.0-alpha.12
• 1.0.0-alpha.13
• 1.0.0-alpha.14
• 1.0.0-alpha.15
• 1.0.0-alpha.16
• 1.0.0-alpha.17

Website

• Product: https://github.com/LemmyNet/lemmy/

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