CVE-2026-26265
Published: 26 February 2026
Summary
CVE-2026-26265 is a high-severity Incorrect Authorization (CWE-863) vulnerability in Discourse Discourse. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 20.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and SI-10 (Information Input Validation).
Deeper analysis
CVE-2026-26265 is an insecure direct object reference (IDOR) vulnerability in Discourse, an open source discussion platform. It affects versions prior to 2025.12.2, 2026.1.1, and 2026.2.0, specifically in the `DirectoryItemsController#index` endpoint. The flaw arises because the `user_field_ids` parameter accepts arbitrary user field IDs without authorization checks, bypassing visibility restrictions like `show_on_profile` or `show_on_user_card` that are enforced elsewhere, such as in `UserCardSerializer` via `Guardian#allowed_user_field_ids`. The vulnerability carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N) and is linked to CWE-863 (Incorrect Authorization) and CWE-639 (Authorization Bypass Through User-Controlled Key).
Any user, including anonymous users, can exploit this vulnerability remotely over the network with low complexity and no privileges required. By sending a GET request to `/directory_items.json?period=all&user_field_ids=<id>` with any private field ID, an attacker can retrieve that field's value for every user in the directory response. This enables bulk exfiltration of sensitive private user data, such as phone numbers, addresses, or other custom fields configured by admins as non-public.
The GitHub Security Advisory (GHSA-crxf-p6jm-vpgw) details patches in Discourse versions 2025.12.2, 2026.1.1, and 2026.2.0, which filter `user_field_ids` against `UserField.public_fields` for non-staff users before building the custom field map. As workarounds, site administrators can remove sensitive data from private user fields or disable the user directory via the `enable_user_directory` site setting.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8859
Vulnerability details
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.…
more
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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The IDOR vulnerability in the public-facing Discourse DirectoryItemsController allows unauthenticated remote attackers to bypass authorization checks and exfiltrate private user data via a standard web API endpoint, directly matching the definition of exploiting an internet-facing application.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Enforces authorization checks on the DirectoryItemsController#index endpoint to prevent unauthorized access to private user fields via arbitrary user_field_ids.
Validates the user_field_ids parameter against user-permitted fields like public_fields, blocking IDOR exploitation and bulk exfiltration of sensitive data.
Applies least privilege to restrict non-staff users from accessing private user fields, mirroring the patch's filtering against UserField.public_fields.