CVE-2026-89324: Basel Post Types <= 1.18 - Unauthenticated Authentication Bypass via Forged Opauth Callback Signature with Hardcoded Fallback Salt

The Basel Post Types plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 1.18. The vulnerability exists because a missing-quotes coding error in the defined() call for SECUREAUTHSALT inside BASELAuth::getconfig() causes PHP to evaluate the constant's value rather than its name, making the check always fail and permanently falling back to the static hardcoded salt 2NlBUibcszrVtNmDnxqDbwCOpLWq91eatIz6O1O that is publicly visible in the theme source code; because this salt is static and known, an attacker can compute a valid Opauth signature entirely offline and submit a forged ?opauth callback to the unauthenticated init hook endpoint processed by registerorlogin. This makes it possible for unauthenticated attackers to authenticate as any existing WordPress user, including administrators, by forging a callback tied to a known target account email address — bypassing all password verification, multi-factor authentication, and ownership checks, and receiving a fully authenticated session cookie via wcsetcustomerauthcookie(). Exploitation requires WooCommerce to be active and at least one Basel social-login provider (Facebook, Google, or VKontakte) to be configured with a valid appid and appsecret in the theme settings.