CVE-2026-54742 Lemmy: `CollectionAdd::Featured` does not check the post is in the community
Community moderators can feature or unfeature posts in other communities by bypassing ownership checks, allowing unauthorized modification of community content listings.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-54742?
CVE-2026-54742 is a medium-severity missing authorization vulnerability in LemmyNet lemmy, published on 19 Aug 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
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.
Weakness: CWE-863
Which versions are affected by CVE-2026-54742?
How do I fix CVE-2026-54742?
No fix has been published for CVE-2026-54742 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-54742 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54742 exists.
Sources
Also known as GHSA-gwfj-h8r7-792v.