The WPMU DEV Dashboard plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 5.0.1. This is due to inconsistent and ambiguous HMAC message construction between the unauthenticated `wdpsso_step1` and `wdpsso_step2` AJAX actions, where step 1 signs and discloses an unseparated concatenation of the token, state, redirect, and domain values, while step 2 verifies an unseparated concatenation that omits the domain field. This makes it possible for unauthenticated attackers, on sites connected to WPMU DEV with Hub SSO enabled and mapped to an administrator, to obtain a valid HMAC from step 1 and replay it to step 2 by moving the domain value into the redirect field, resulting in an authenticated administrator session.

The WPMU DEV Dashboard plugin for WordPress contains a critical authentication bypass vulnerability affecting all versions up to and including 5.0.1. The flaw stems from inconsistent HMAC message construction between two AJAX actions (wdpsso_step1 and wdpsso_step2) used in the Hub SSO flow. Step 1 signs a concatenation of token, state, redirect, and domain values, while step 2 verifies a concatenation that omits the domain field. An unauthenticated attacker can exploit this by obtaining a valid HMAC from step 1 and replaying it to step 2, shifting the domain value into the redirect field. This results in a fully authenticated administrator session without valid credentials. The attack is viable on sites connected to WPMU DEV with Hub SSO enabled and mapped to an administrator account. No authentication is required to exploit this vulnerability.