CVE-2026-54742 PUBLISHED

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

Assigner: GitHub_M
Reserved: 15.06.2026 Published: 19.08.2026 Updated: 19.08.2026

Lemmy 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.

Metrics

CVSS Vector: 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
CVSS Score: 5.1

Product Status

Vendor LemmyNet
Product lemmy
Versions
  • Version < 0.19.19 is affected
  • Version >= 1.0.0-alpha.0, < 1.0.0-alpha.20 is affected

References

Problem Types

  • CWE-863: Incorrect Authorization CWE