diff --git a/wp-activate.php b/wp-activate.php
index a796cc5e48..7c59656045 100644
--- a/wp-activate.php
+++ b/wp-activate.php
@@ -18,6 +18,48 @@ if ( !is_multisite() ) {
 	die();
 }
 
+$valid_error_codes = array( 'already_active', 'blog_taken' );
+
+list( $activate_path ) = explode( '?', wp_unslash( $_SERVER['REQUEST_URI'] ) );
+$activate_cookie = 'wp-activate-' . COOKIEHASH;
+
+$key    = '';
+$result = null;
+
+if ( ! empty( $_GET['key'] ) ) {
+	$key = $_GET['key'];
+} elseif ( ! empty( $_POST['key'] ) ) {
+	$key = $_POST['key'];
+}
+
+if ( $key ) {
+	$redirect_url = remove_query_arg( 'key' );
+
+	if ( $redirect_url !== remove_query_arg( false ) ) {
+		setcookie( $activate_cookie, $key, 0, $activate_path, COOKIE_DOMAIN, is_ssl(), true );
+		wp_safe_redirect( $redirect_url );
+		exit;
+	} else {
+		$result = wpmu_activate_signup( $key );
+	}
+}
+
+if ( $result === null && isset( $_COOKIE[ $activate_cookie ] ) ) {
+	$key    = $_COOKIE[ $activate_cookie ];
+	$result = wpmu_activate_signup( $key );
+	setcookie( $activate_cookie, ' ', time() - YEAR_IN_SECONDS, $activate_path, COOKIE_DOMAIN, is_ssl(), true );
+}
+
+if ( $result === null || ( is_wp_error( $result ) && 'invalid_key' === $result->get_error_code() ) ) {
+	status_header( 404 );
+} elseif ( is_wp_error( $result ) ) {
+	$error_code = $result->get_error_code();
+
+	if ( ! in_array( $error_code, $valid_error_codes ) ) {
+		status_header( 400 );
+	}
+}
+
 if ( is_object( $wp_object_cache ) )
 	$wp_object_cache->cache_enabled = false;
 
@@ -63,12 +105,13 @@ function wpmu_activate_stylesheet() {
 	<?php
 }
 add_action( 'wp_head', 'wpmu_activate_stylesheet' );
+add_action( 'wp_head', 'wp_sensitive_page_meta' );
 
 get_header();
 ?>
 
 <div id="content" class="widecolumn">
-	<?php if ( empty($_GET['key']) && empty($_POST['key']) ) { ?>
+	<?php if ( ! $key ) { ?>
 
 		<h2><?php _e('Activation Key Required') ?></h2>
 		<form name="activateform" id="activateform" method="post" action="<?php echo network_site_url('wp-activate.php'); ?>">
@@ -82,28 +125,25 @@ get_header();
 		</form>
 
 	<?php } else {
-
-		$key = !empty($_GET['key']) ? $_GET['key'] : $_POST['key'];
-		$result = wpmu_activate_signup( $key );
-		if ( is_wp_error($result) ) {
-			if ( 'already_active' == $result->get_error_code() || 'blog_taken' == $result->get_error_code() ) {
-			    $signup = $result->get_error_data();
-				?>
-				<h2><?php _e('Your account is now active!'); ?></h2>
-				<?php
-				echo '<p class="lead-in">';
-				if ( $signup->domain . $signup->path == '' ) {
-					printf( __('Your account has been activated. You may now <a href="%1$s">log in</a> to the site using your chosen username of &#8220;%2$s&#8221;. Please check your email inbox at %3$s for your password and login instructions. If you do not receive an email, please check your junk or spam folder. If you still do not receive an email within an hour, you can <a href="%4$s">reset your password</a>.'), network_site_url( 'wp-login.php', 'login' ), $signup->user_login, $signup->user_email, wp_lostpassword_url() );
-				} else {
-					printf( __('Your site at <a href="%1$s">%2$s</a> is active. You may now log in to your site using your chosen username of &#8220;%3$s&#8221;. Please check your email inbox at %4$s for your password and login instructions. If you do not receive an email, please check your junk or spam folder. If you still do not receive an email within an hour, you can <a href="%5$s">reset your password</a>.'), 'http://' . $signup->domain, $signup->domain, $signup->user_login, $signup->user_email, wp_lostpassword_url() );
-				}
-				echo '</p>';
+		if ( is_wp_error( $result ) && in_array( $result->get_error_code(), $valid_error_codes ) ) {
+			$signup = $result->get_error_data();
+			?>
+			<h2><?php _e('Your account is now active!'); ?></h2>
+			<?php
+			echo '<p class="lead-in">';
+			if ( $signup->domain . $signup->path == '' ) {
+				printf( __('Your account has been activated. You may now <a href="%1$s">log in</a> to the site using your chosen username of &#8220;%2$s&#8221;. Please check your email inbox at %3$s for your password and login instructions. If you do not receive an email, please check your junk or spam folder. If you still do not receive an email within an hour, you can <a href="%4$s">reset your password</a>.'), network_site_url( 'wp-login.php', 'login' ), $signup->user_login, $signup->user_email, wp_lostpassword_url() );
 			} else {
-				?>
-				<h2><?php _e('An error occurred during the activation'); ?></h2>
-				<?php
-			    echo '<p>'.$result->get_error_message().'</p>';
+				printf( __('Your site at <a href="%1$s">%2$s</a> is active. You may now log in to your site using your chosen username of &#8220;%3$s&#8221;. Please check your email inbox at %4$s for your password and login instructions. If you do not receive an email, please check your junk or spam folder. If you still do not receive an email within an hour, you can <a href="%5$s">reset your password</a>.'), 'http://' . $signup->domain, $signup->domain, $signup->user_login, $signup->user_email, wp_lostpassword_url() );
 			}
+			echo '</p>';
+		} elseif ( $result === null || is_wp_error( $result ) ) {
+			?>
+			<h2><?php _e('An error occurred during the activation'); ?></h2>
+			<?php if ( is_wp_error( $result ) ) {
+				echo '<p>' . $result->get_error_message() . '</p>';
+			} ?>
+			<?php
 		} else {
 			$url = isset( $result['blog_id'] ) ? get_blogaddress_by_id( (int) $result['blog_id'] ) : '';
 			$user = get_userdata( (int) $result['user_id'] );
diff --git a/wp-includes/general-template.php b/wp-includes/general-template.php
index 0b28feb16e..d2ba269aad 100644
--- a/wp-includes/general-template.php
+++ b/wp-includes/general-template.php
@@ -2363,6 +2363,24 @@ function wp_no_robots() {
 	echo "<meta name='robots' content='noindex,follow' />\n";
 }
 
+/**
+ * Display a noindex,noarchive meta tag and referrer origin-when-cross-origin meta tag.
+ *
+ * Outputs a noindex,noarchive meta tag that tells web robots not to index or cache the page content.
+ * Outputs a referrer origin-when-cross-origin meta tag that tells the browser not to send the full
+ * url as a referrer to other sites when cross-origin assets are loaded.
+ *
+ * Typical usage is as a wp_head callback. add_action( 'wp_head', 'wp_sensitive_page_meta' );
+ *
+ * @since 5.0.0
+ */
+function wp_sensitive_page_meta() {
+	?>
+	<meta name='robots' content='noindex,noarchive' />
+	<meta name='referrer' content='strict-origin-when-cross-origin' />
+	<?php
+}
+
 /**
  * Whether the user should have a WYSIWIG editor.
  *
diff --git a/wp-login.php b/wp-login.php
index 36b41dba36..3c5ff8e74d 100644
--- a/wp-login.php
+++ b/wp-login.php
@@ -34,7 +34,7 @@ function login_header( $title = 'Log In', $message = '', $wp_error = '' ) {
 	global $error, $interim_login, $action;
 
 	// Don't index any of these forms
-	add_action( 'login_head', 'wp_no_robots' );
+	add_action( 'login_head', 'wp_sensitive_page_meta' );
 
 	if ( wp_is_mobile() )
 		add_action( 'login_head', 'wp_login_viewport_meta' );