Lemmy: `CollectionAdd::Featured` does not check the post is in the community

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-54742
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-19 20:17:17 UTC
Updated2026-08-19 20:17:17 UTC
DescriptionLemmy is a link aggregator and forum for the fediverse. From 0.19.18 until 0.19.19 and 1.0.0-alpha.20, a community moderator can feature or unfeature posts in other communities through federated CollectionAdd and CollectionRemove activities using CollectionType::Featured. After verify_mod_action authorizes the actor against self.community(), the receive handlers in crates/apub/activities/src/community/collection_add.rs and crates/apub/activities/src/community/collection_remove.rs dereference self.object as an ApubPost and update featured_community without verifying that post.community_id equals community.id. A moderator can therefore target an unrelated post owned by another community, push it into featured feeds and listings, or undo another community's legitimate curation decision. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.20.

Risk And Classification

Primary CVSS: v4.0 5.1 MEDIUM from [email protected]

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-863 | CWE-863 CWE-863: Incorrect Authorization

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary5.1MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED5.1MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
High
User Interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA LemmyNet Lemmy affected < 0.19.19 Not specified
CNA LemmyNet Lemmy affected >= 1.0.0-alpha.0, < 1.0.0-alpha.20 Not specified

References

ReferenceSourceLinkTags
github.com/LemmyNet/lemmy/commit/108d78c592cc88bac2b0bf52ca6631be54f6fb23 [email protected] github.com
github.com/LemmyNet/lemmy/commit/abe256243822526dcd4bca857f7c0adeb49944f5 [email protected] github.com
join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19 [email protected] join-lemmy.org
github.com/LemmyNet/lemmy/pull/6500 [email protected] github.com
github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.20 [email protected] github.com
github.com/LemmyNet/lemmy/pull/6501 [email protected] github.com
github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v [email protected] github.com
github.com/LemmyNet/lemmy/releases/tag/0.19.19 [email protected] github.com
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