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 verifymodaction authorizes the actor against self.community(), the receive handlers in crates/apub/activities/src/community/collectionadd.rs and crates/apub/activities/src/community/collectionremove.rs dereference self.object as an ApubPost and update featuredcommunity without verifying that post.communityid 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.
{
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54742.json",
"cwe_ids": [
"CWE-863"
]
}{
"extracted_events": [
{
"introduced": "0"
},
{
"fixed": "0.19.19"
},
{
"introduced": "1.0.0-alpha.0"
},
{
"fixed": "1.0.0-alpha.20"
}
],
"source": [
"AFFECTED_FIELD",
"REFERENCES"
]
}