* added security condition to check that one logged-in user cannot activate another one user via email activation link;

* fixed double handler of email activation link (wp_die doesn't stop the script for some reason);
* added redirects to login page with error notices instead of wp_die text;

includes/common/class-users.php

@@ -279,6 +279,8 @@ class Users {
 		 * @param {int}    $expiration Expiration timestamp. Since 2.8.7.
 		 */
 		do_action( 'um_after_user_hash_is_changed', $user_id, $hash, $expiration );
+
+		$this->remove_cache( $user_id ); // Don't remove this line. It's required removing cache duplicate for the force case when re-send activation email.
 	}
 
 	/**

includes/core/class-permalinks.php

@@ -113,16 +113,24 @@ if ( ! class_exists( 'um\core\Permalinks' ) ) {
 				 isset( $_REQUEST['user_id'] ) && is_numeric( $_REQUEST['user_id'] ) ) { // valid token
 
 				$user_id = absint( $_REQUEST['user_id'] );
+				if ( is_user_logged_in() && get_current_user_id() !== $user_id ) {
+					// Cannot activate another user account. Please log out and try again.
+					wp_safe_redirect( um_user_profile_url( get_current_user_id() ) );
+					exit;
+				}
+
 				delete_option( "um_cache_userdata_{$user_id}" );
 
 				$account_secret_hash = get_user_meta( $user_id, 'account_secret_hash', true );
 				if ( empty( $account_secret_hash ) || strtolower( sanitize_text_field( $_REQUEST['hash'] ) ) !== strtolower( $account_secret_hash ) ) {
-					wp_die( esc_html__( 'This activation link is expired or have already been used.', 'ultimate-member' ) );
+					wp_safe_redirect( add_query_arg( 'err', 'activation_link_used', um_get_core_page( 'login' ) ) );
+					exit;
 				}
 
 				$account_secret_hash_expiry = get_user_meta( $user_id, 'account_secret_hash_expiry', true );
 				if ( ! empty( $account_secret_hash_expiry ) && time() > $account_secret_hash_expiry ) {
-					wp_die( esc_html__( 'This activation link is expired.', 'ultimate-member' ) );
+					wp_safe_redirect( add_query_arg( 'err', 'activation_link_expired', um_get_core_page( 'login' ) ) );
+					exit;
 				}
 
 				$redirect              = um_get_core_page( 'login', 'account_active' );
@@ -141,15 +149,7 @@ if ( ! class_exists( 'um\core\Permalinks' ) ) {
 				// log in automatically
 				$login = ! empty( $user_role_data['login_email_activate'] ); // Role setting "Login user after validating the activation link?"
 				if ( ! is_user_logged_in() && $login ) {
-					$user = get_userdata( $user_id );
-
-					// update wp user
-					wp_set_current_user( $user_id, $user->user_login );
-					wp_set_auth_cookie( $user_id );
-
-					ob_start();
-					do_action( 'wp_login', $user->user_login, $user );
-					ob_end_clean();
+					UM()->user()->auto_login( $user_id );
 				}
 
 				/**

includes/core/class-user.php

@@ -1362,7 +1362,7 @@ if ( ! class_exists( 'um\core\User' ) ) {
 		<?php UM()->user()->auto_login( 10, true ); ?>
 		 *
 		 */
-		function auto_login( $user_id, $rememberme = 0 ) {
+		public function auto_login( $user_id, $rememberme = 0 ) {
 
 			wp_set_current_user( $user_id );
 

includes/core/um-actions-misc.php

@@ -176,6 +176,12 @@ function um_add_update_notice( $args ) {
 			case 'invalid_nonce':
 				$err = __( 'An error has been encountered. Probably page was cached. Please try again.', 'ultimate-member' );
 				break;
+			case 'activation_link_used':
+				$err = __( 'This activation link is expired or have already been used.', 'ultimate-member' );
+				break;
+			case 'activation_link_expired':
+				$err = __( 'This activation link is expired.', 'ultimate-member' );
+				break;
 		}
 	}
 	// phpcs:enable WordPress.Security.NonceVerification -- used for echo and already verified here.