Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, unauthenticated users can det…
Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, unauthenticated users can determine whether a specific user is a member of a private group by observing changes in directory results when using the `exclude_groups` parameter. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. As a workaround, disable public access to the user directory via Admin → Settings → hide user profiles from public.
The product behaves differently or sends different responses under different circumstances in a way that is observable to an unauthorized actor.
https://cwe.mitre.org/data/definitions/203.html →Open in CWE collection →An adversary discovers the structure, function, and composition of a type of computer software through black box analysis techniques. 'Black Box' methods involve interacting with the software indirectly, in the absence of direct access to the executable object. Such analysis typically involves interacting with the software at the boundaries of where the software interfaces with a larger execution environment, such as input-output vectors, libraries, or APIs. Black Box Reverse Engineering also refers to gathering physical side effects of a hardware device, such as electromagnetic radiation or sounds.
https://capec.mitre.org/data/definitions/189.html →Open in CAPEC collection →