An unauthenticated attacker can capture the signed output from the first step - which includes the token, state, redirect, and domain parameters - and manipulate the input to the second step. By moving the domain value into the redirect field, the attacker creates a payload that satisfies the validation logic in the second AJAX action, which unexpectedly omits the domain field from its verification check. Successful exploitation grants the attacker an authenticated administrator session, posing a significant risk for complete site takeover. Organizations using the WPMU DEV Dashboard with Hub SSO enabled are at risk and should prioritize immediate remediation.

Impact

Successful exploitation of CVE-2026-76581 allows unauthenticated actors to gain full administrative control over the affected WordPress installation. This provides unrestricted access to site configurations, data, and themes, effectively bypassing all authentication controls. Given the widespread use of WPMU DEV plugins, the number of potentially affected WordPress environments is high, particularly among managed hosting services.

Recommendation

• Update the WPMU DEV Dashboard plugin to version 5.0.2 or later immediately to resolve the flawed HMAC construction logic.
• Disable the "Hub SSO" feature if it is not currently required for administrative access while the patch process is underway.
• Audit access logs for repetitive or unusual POST requests targeting admin-ajax.php involving the wdpsso_step1 and wdpsso_step2 actions, particularly those demonstrating atypical parameter concatenation or unexpected redirects.