Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, an IDOR vulnerability in the directory items endpoint allows any user, including anonymous users, to retrieve private user field values for all users in the directory. The user_field_ids parameter in DirectoryItemsController#index accepts arbitrary user field IDs without authorization checks, bypassing the visibility restrictions (show_on_profile / show_on_user_card) that are enforced elsewhere (e.g., UserCardSerializer via Guardian#allowed_user_field_ids).

An attacker can request GET /directory_items.json?period=all&user_field_ids=<id> with any private field ID and receive that field's value for every user in the directory response. This enables bulk exfiltration of private user data such as phone numbers, addresses, or other sensitive custom fields that admins have explicitly configured as non-public. The issue is patched in versions 2025.12.2, 2026.1.1, and 2026.2.0 by filtering user_field_ids against UserField.public_fields for non-staff users before building the custom field map.

As a workaround, site administrators can remove sensitive data from private user fields, or disable the user directory via the enable_user_directory site setting.