The WPMU DEV Dashboard plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 5.0.0. On sites not yet connected to the WPMU DEV Hub — the default state after installation — the site API key that keys the WDP-AUTH request signature is empty, making the signature verified by validate_hash() trivially forgeable; version 5.0.0 additionally removed the replay check in validate_nonce(), and the remote handler is bound to the public init hook with no capability check. This makes it possible for unauthenticated attackers to invoke privileged Hub actions — including installing and activating a plugin from an attacker-supplied URL (resulting in remote code execution), deleting plugins and themes, upgrading WordPress core, or logging in as an administrator via SSO. Sites connected to a WPMU DEV account, which have a non-empty 64-character API key, are not affected.
