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CVE-2026-76581 – Authentication Bypass to Administrator – WPMU DEV Dashboard WordPress Plugin ≤ 5.0.

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Summary

CVE-2026-76581 is a critical authentication bypass vulnerability in the WPMU DEV Dashboard plugin for WordPress, affecting all versions up to and including 5.0.1. The flaw resides in the plugin’s Hub Single Sign-On (SSO) implementation and allows an unauthenticated attacker to obtain a valid HMAC signature from one SSO step and replay it against a second, differently-canonicalized SSO step to forge an authenticated administrator session. The issue carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: The plugin exposes two unauthenticated AJAX actions, wdpsso_step1 and wdpsso_step2, that are supposed to jointly validate an HMAC over a set of SSO parameters (token, state, redirect, and domain). Step 1 signs and discloses an unseparated concatenation of token + state + redirect + domain, while step 2 verifies an unseparated concatenation that omits the domain field.
  • Trigger conditions: Because the two steps canonicalize the signed message differently, an attacker can take a valid HMAC returned by step 1 and replay it against step 2 by moving the value that was previously in the domain field into the redirect field — the signature still validates due to the inconsistent message construction (CWE-347: Improper Verification of Cryptographic Signature).
  • Prerequisites: Exploitation requires that the target site is connected to the WPMU DEV Hub with Hub SSO enabled and mapped to an administrator account.
  • Attack vector: Network-based, requiring no authentication and no user interaction — both AJAX actions involved are reachable by unauthenticated requests.
  • Impact: Successful exploitation results in the attacker obtaining a fully authenticated administrator session on the affected WordPress site, leading to complete compromise of confidentiality, integrity, and availability of the site.

Affected software

  • WPMU DEV Dashboard plugin for WordPress, all versions from 0 up to and including 5.0.1

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: At the time of publication, no patched release beyond 5.0.1 has been confirmed. Security teams should monitor the WPMU DEV Dashboard plugin page for an update that fixes the HMAC canonicalization inconsistency between wdpsso_step1 and wdpsso_step2, and apply it as soon as it becomes available.
  • If no patch is available:
    • Where feasible, temporarily disable Hub SSO / disconnect the site from the WPMU DEV Hub until a fix is released, particularly on sites where SSO is mapped to an administrator account.
    • Restrict or monitor access to the plugin’s wdpsso_step1 and wdpsso_step2 AJAX endpoints (admin-ajax.php with these actions) at the WAF or reverse-proxy layer.
    • Review WordPress administrator account activity and audit logs for unexpected new sessions or logins correlating with these AJAX actions.
    • Ensure the WPMU DEV Dashboard plugin is kept on the latest available version and subscribe to vendor/plugin update notifications.

References

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