CVE-2026-54742
MediumCVSS 5.1Exploitation Probability (EPSS)
Low risk35th percentile - higher than 35% of all known CVEs
Summary
Lemmy, a link aggregator and forum for the fediverse, versions 0.19.18 to 0.19.19 and 1.0.0-alpha.20, allows a community moderator to feature or unfeature posts in other communities via federated CollectionAdd and CollectionRemove activities. Lack of verification that the post belongs to the community enables manipulation of other communities' content.
Risk Assessment
The risk includes content integrity violation in other communities, unauthorized featuring of posts, or removal of legitimate curation decisions. This could lead to misinformation and loss of trust.
Recommendation
Upgrade Lemmy to version 0.19.19 or 1.0.0-alpha.20 (or later). Also, monitor federated activities for anomalies.
Original NVD description (English source)
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.