Ticket #44347: 44347.wp-includes.user.php.diff

user.php

@@ -2439 +2439 @@
         }
 
         /**
+         * Additional checks for cross-referenced email and username among existing accounts.
+         * Prevent using existing email address as username and vice versa.
+         * Do not allow an existing email address to be used as a username of the new account.
+         * Do not allow an existing username to be used as the email address of the new account.
+         */
+        
+        // Check if username is being used as the email address of another account.
+        if ( email_exists( $sanitized_user_login ) ) {
+                $errors->add( 'email_exists', __( '<strong>ERROR</strong>: This username is invalid because it is already the email address of another account.' ) );
+        }
+
+        // Check if email address is being used as the username of another account.
+        if ( '' !== $user_email && username_exists( $user_email ) ) {
+                $errors->add( 'username_exists', __( '<strong>ERROR</strong>: This email address cannot be used because it is already the username of another account.' ) );
+        }
+
+        /**
          * Fires when submitting registration form data, before the user is created.
          *
          * @since 2.1.0