CVE-2026-54740: CWE-862: Missing Authorization in LemmyNet lemmy
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.
AI Analysis
Technical Summary
CVE-2026-54740 is a missing authorization vulnerability (CWE-862) in LemmyNet lemmy, a federated link aggregator and forum software. In affected versions prior to 0.19.19 and 1.0.0-alpha.18, the federated moderation mechanism improperly allows a lower-ranked remote moderator to remove a higher-ranked moderator by sending a signed ActivityPub Remove activity. The local API enforces moderator rank checks, but the federated CollectionRemove handler does not verify that the actor outranks the target moderator before processing the removal. This discrepancy enables privilege escalation within federated communities. The vulnerability is resolved in versions 0.19.19 and 1.0.0-alpha.18.
Potential Impact
An attacker with lower-ranked remote moderator privileges can remove higher-ranked moderators from a community, effectively escalating their privileges and disrupting community moderation controls. This can lead to unauthorized moderator removals and potential abuse of moderation functions. The vulnerability does not impact confidentiality or availability but has a high impact on integrity of moderation roles.
Mitigation Recommendations
Upgrade LemmyNet lemmy to version 0.19.19 or 1.0.0-alpha.18 or later, where this authorization flaw is fixed. No other mitigations are indicated in the vendor advisory. Patch status is not explicitly stated but the fix is included in these versions.
CVE-2026-54740: CWE-862: Missing Authorization in LemmyNet lemmy
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.
CVSS v3.1
Score 6.5medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-54740 is a missing authorization vulnerability (CWE-862) in LemmyNet lemmy, a federated link aggregator and forum software. In affected versions prior to 0.19.19 and 1.0.0-alpha.18, the federated moderation mechanism improperly allows a lower-ranked remote moderator to remove a higher-ranked moderator by sending a signed ActivityPub Remove activity. The local API enforces moderator rank checks, but the federated CollectionRemove handler does not verify that the actor outranks the target moderator before processing the removal. This discrepancy enables privilege escalation within federated communities. The vulnerability is resolved in versions 0.19.19 and 1.0.0-alpha.18.
Potential Impact
An attacker with lower-ranked remote moderator privileges can remove higher-ranked moderators from a community, effectively escalating their privileges and disrupting community moderation controls. This can lead to unauthorized moderator removals and potential abuse of moderation functions. The vulnerability does not impact confidentiality or availability but has a high impact on integrity of moderation roles.
Mitigation Recommendations
Upgrade LemmyNet lemmy to version 0.19.19 or 1.0.0-alpha.18 or later, where this authorization flaw is fixed. No other mitigations are indicated in the vendor advisory. Patch status is not explicitly stated but the fix is included in these versions.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-15T23:07:33.233Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a86e0f3acd9273b49838518
Added to database: 08/20/2026, 11:11:47 UTC
Last enriched: 08/20/2026, 11:22:54 UTC
Last updated: 08/20/2026, 20:07:44 UTC
Views: 3
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