n8n versions before 1.123.80, from 2.0.0 before 2.39.6, and from 2.40.0 before 2.40.1 contain a NoSQL injection vulnerability in the MongoDB Chat Memory node that fails to validate the sessionId parameter. Unauthenticated attackers can supply MongoDB query operators in the sessionId field to access conversation histories from other users and perform unauthorized write and delete operations.