diff --git a/wp-activate.php b/wp-activate.php
index 6aae1ca8a0..d24f26a266 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 );
+	}
+}
+
 nocache_headers();
 
 if ( is_object( $wp_object_cache ) )
@@ -69,13 +111,14 @@ function wpmu_activate_stylesheet() {
 	<?php
 }
 add_action( 'wp_head', 'wpmu_activate_stylesheet' );
+add_action( 'wp_head', 'wp_sensitive_page_meta' );
 
 get_header( 'wp-activate' );
 ?>
 
 <div id="signup-content" class="widecolumn">
 	<div class="wp-activate-container">
-	<?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'); ?>">
@@ -89,42 +132,39 @@ get_header( 'wp-activate' );
 		</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 . $signup->path == '' ) {
-					printf(
-						/* translators: 1: login URL, 2: username, 3: user email, 4: lost password URL */
-						__( 'Your account has been activated. You may now <a href="%1$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,
-						$signup->user_email,
-						wp_lostpassword_url()
-					);
-				} else {
-					printf(
-						/* translators: 1: site URL, 2: username, 3: user email, 4: lost password URL */
-						__( 'Your site at %1$s is active. You may now log in to your 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$s">reset your password</a>.' ),
-						sprintf( '<a href="http://%1$s">%1$s</a>', $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 . $signup->path == '' ) {
+				printf(
+				/* translators: 1: login URL, 2: username, 3: user email, 4: lost password URL */
+					__( 'Your account has been activated. You may now <a href="%1$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>
-				<p><?php echo $result->get_error_message(); ?></p>
-				<?php
+				printf(
+				/* translators: 1: site URL, 2: username, 3: user email, 4: lost password URL */
+					__( 'Your site at %1$s is active. You may now log in to your 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$s">reset your password</a>.' ),
+					sprintf( '<a href="http://%1$s">%1$s</a>', $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 ) ) : ?>
+				<p><?php echo $result->get_error_message(); ?></p>
+			<?php endif; ?>
+			<?php
 		} else {
 			$url = isset( $result['blog_id'] ) ? get_home_url( (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 33fcfbb675..30497648af 100644
--- a/wp-includes/general-template.php
+++ b/wp-includes/general-template.php
@@ -2812,6 +2812,24 @@ 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
+}
+
 /**
  * Display site icon meta tags.
  *
diff --git a/wp-includes/version.php b/wp-includes/version.php
index f841cdb024..c56fcee262 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9.9-alpha-44020';
+$wp_version = '4.9.9-alpha-44024';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-login.php b/wp-login.php
index ffd86c1e20..be715dfa9f 100644
--- a/wp-login.php
+++ b/wp-login.php
@@ -34,7 +34,7 @@ function login_header( $title = 'Log In', $message = '', $wp_error = null ) {
 	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' );
 
 	add_action( 'login_head', 'wp_login_viewport_meta' );