diff --git a/wp-admin/about.php b/wp-admin/about.php
index 4a25394b3a..a58221a5c8 100644
--- a/wp-admin/about.php
+++ b/wp-admin/about.php
@@ -64,6 +64,26 @@ require_once ABSPATH . 'wp-admin/admin-header.php';
 		<div class="about__section has-subtle-background-color">
 			<div class="column">
 				<h2><?php _e( 'Maintenance and Security Releases' ); ?></h2>
+				<p>
+					<?php
+					printf(
+						/* translators: %s: WordPress version number */
+						__( '<strong>Version %s</strong> addressed one security issue.' ),
+						'5.5.9'
+					);
+					?>
+					<?php
+					printf(
+						/* translators: %s: HelpHub URL */
+						__( 'For more information, see <a href="%s">the release notes</a>.' ),
+						sprintf(
+							/* translators: %s: WordPress version */
+							esc_url( __( 'https://wordpress.org/support/wordpress-version/version-%s/' ) ),
+							sanitize_title( '5.5.9' )
+						)
+					);
+					?>
+				</p>
 				<p>
 					<?php
 					printf(
diff --git a/wp-includes/version.php b/wp-includes/version.php
index dde6098e93..8400766ed3 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5.8';
+$wp_version = '5.5.9';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.