Misskey: Lack of proper permission checks in Direct Messaging feature

Misskey is an open source, federated social media platform. Versions 2025.3.2 and later, but prior to 2026.5.4, contain a vulnerability where a lack of proper permission checks allows access to certain data points from the Direct Messages (formerly Chat) feature, regardless of account permissions. This vulnerability occurs whether or not federation is enabled. Notes created with "specified" visibility (formerly "direct" visibility) are not affected. This issue has been fixed in version 2026.5.4.