Discourse is an open source discussion platform. Prior to versions 3.5.3, 2025.11.1, and 2025.12.0, an attacker who knows part of a username can find the user and their full name via UI or API, even when enable_names is disabled. Versions 3.5.3, 2025.11.1, and 2025.12.0 contain a fix.
When trying to keep information confidential, an attacker can often infer some of the information by using statistics.