Misskey is an open source, decentralized microblogging platform. Misskey doesn't perform proper normalization on the JSON structures of incoming signed ActivityPub activity objects before processing them, allowing threat actors to spoof the contents of signed activities and impersonate the authors of the original activities. This vulnerability is fixed in 2024.5.0.
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.