Executive brief
WP OAuth Server is a WordPress plugin that enables single sign-on authentication via OpenID Connect, allowing external applications to trust user identity assertions issued by the site. The plugin fails to properly bind identity assertions to specific authorization requests, instead returning the assertion of whichever user authenticated most recently. An attacker with a Subscriber role or higher can exploit this to obtain a valid identity assertion for any user, including administrators, and gain unauthorized access to all applications using the site for single sign-on.
Technical details
The vulnerability is an authentication bypass in the OpenID Connect identity assertion generation mechanism (CWE-287: Improper Authentication). The vulnerable component fails to bind issued ID tokens to the specific authorization grant being exchanged, allowing privilege escalation via token substitution. Any authenticated user with Subscriber role or above can trigger the issuance of identity assertions for other users by manipulating the authentication flow; the fix is available in version 6.4.0.
Affected products
- MiniOrange WP OAuth Server before 6.4.0
Timeline
- 2026-09-21: disclosed
- 2026-09-21: patched: Fixed in version 6.4.0