The Qode Membership plugin for WordPress is vulnerable to Authentication Bypass leading to Account Takeover in all versions up to, and including, 2.0.6.2 via the qode_membership_check_facebook_user AJAX action. This is due to a typographic error in the Facebook OAuth token verification guard within the qode_membership_login_user_from_social_network function — the guard condition tests an undefined variable ($check_social_useqoder instead of $check_social_user), causing empty() to always return true and rendering the Graph API token verification branch dead code, leaving wp_set_auth_cookie() reachable with no credential or token validation whatsoever. This makes it possible for unauthenticated attackers to log in as any existing WordPress account — including Administrator-level accounts — by supplying a known or enumerated administrator login name (rather than an email address) in the response[email] parameter, which the fallback path in get_user_by('login', $email) resolves to the matching account.
Exploitation does require harvesting a valid qode_validate_facebook_login nonce, but this nonce is rendered on any public front-end page containing the [qode_user_login] or [qode_user_register] shortcode and is therefore obtainable without any prior authentication.
Attack Parameters
Impact Assessment
CVSS Vector v3.1