Rocket.Chat is an open-source, secure, fully customizable communications platform. Prior to versions 7.10.8, 7.11.5, 7.12.5, 7.13.4, 8.0.2, 8.1.1, and 8.2.0, a NoSQL injection vulnerability exists in Rocket.Chat's account service used in the ddp-streamer micro service that allows unauthenticated attackers to manipulate MongoDB queries during authentication. The vulnerability is located in the username-based login flow where user-supplied input is directly embedded into a MongoDB query selector without validation. An attacker can inject MongoDB operator expressions (e.g., { $regex: '.*' }) in place of a username string, causing the database query to match unintended user records. This issue has been patched in versions 7.10.8, 7.11.5, 7.12.5, 7.13.4, 8.0.2, 8.1.1, and 8.2.0.