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Vulnerability · Published Aug 19, 2026 · Assigned by GitHub_M

CVE-2026-54742Lemmy: `CollectionAdd::Featured` does not check the post is in the community

Medium 5.1

In plain English

A medium-severity incorrect authorization in lemmy from LemmyNet. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 46% of all known vulnerabilities).

Severity (CVSS 4.0)5.1Medium
Exploit odds (30 days)0.5%top 53.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

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.

Affected products (as reported)

VendorProductVersions
LemmyNet lemmy < 0.19.19>= 1.0.0-alpha.0, < 1.0.0-alpha.20

Weakness: CWE-863 · 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

References