diff --git a/src/wp-admin/admin-functions.php b/src/wp-admin/admin-functions.php
index a9ff3f44b99f7..6ce4e06c47007 100644
--- a/src/wp-admin/admin-functions.php
+++ b/src/wp-admin/admin-functions.php
@@ -9,6 +9,11 @@
  * @subpackage Administration
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 _deprecated_file( basename( __FILE__ ), '2.5.0', 'wp-admin/includes/admin.php' );
 
 /** WordPress Administration API: Includes all Administration functions. */
diff --git a/src/wp-admin/admin-header.php b/src/wp-admin/admin-header.php
index fc836c20a2c1d..f86a0fadde085 100644
--- a/src/wp-admin/admin-header.php
+++ b/src/wp-admin/admin-header.php
@@ -6,6 +6,11 @@
  * @subpackage Administration
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 header( 'Content-Type: ' . get_option( 'html_type' ) . '; charset=' . get_option( 'blog_charset' ) );
 if ( ! defined( 'WP_ADMIN' ) ) {
 	require_once __DIR__ . '/admin.php';
diff --git a/src/wp-admin/custom-background.php b/src/wp-admin/custom-background.php
index 37b8c3d8b8403..bbd56bdb6cee2 100644
--- a/src/wp-admin/custom-background.php
+++ b/src/wp-admin/custom-background.php
@@ -9,6 +9,11 @@
  * @subpackage Administration
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 _deprecated_file( basename( __FILE__ ), '5.3.0', 'wp-admin/includes/class-custom-background.php' );
 
 /** Custom_Background class */
diff --git a/src/wp-admin/custom-header.php b/src/wp-admin/custom-header.php
index d89f03bbaab2a..31c78dcb5b372 100644
--- a/src/wp-admin/custom-header.php
+++ b/src/wp-admin/custom-header.php
@@ -9,6 +9,11 @@
  * @subpackage Administration
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 _deprecated_file( basename( __FILE__ ), '5.3.0', 'wp-admin/includes/class-custom-image-header.php' );
 
 /** Custom_Image_Header class */
diff --git a/src/wp-admin/menu-header.php b/src/wp-admin/menu-header.php
index 9b38e6f77d9d0..caf7d8f4877f4 100644
--- a/src/wp-admin/menu-header.php
+++ b/src/wp-admin/menu-header.php
@@ -6,6 +6,11 @@
  * @subpackage Administration
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /**
  * The current page.
  *
diff --git a/src/wp-admin/menu.php b/src/wp-admin/menu.php
index 8076479220bec..18ec4f1dde599 100644
--- a/src/wp-admin/menu.php
+++ b/src/wp-admin/menu.php
@@ -6,6 +6,11 @@
  * @subpackage Administration
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /**
  * Constructs the admin menu.
  *
diff --git a/src/wp-admin/network/menu.php b/src/wp-admin/network/menu.php
index 73cc86b23484d..852c36004cbab 100644
--- a/src/wp-admin/network/menu.php
+++ b/src/wp-admin/network/menu.php
@@ -7,6 +7,11 @@
  * @since 3.1.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /* translators: Network menu item. */
 $menu[2] = array( __( 'Dashboard' ), 'manage_network', 'index.php', '', 'menu-top menu-top-first menu-icon-dashboard', 'menu-dashboard', 'dashicons-dashboard' );
 
diff --git a/src/wp-admin/options-head.php b/src/wp-admin/options-head.php
index 9dba3703c5ad7..ce5e1a26cb7c6 100644
--- a/src/wp-admin/options-head.php
+++ b/src/wp-admin/options-head.php
@@ -8,6 +8,11 @@
  * @subpackage Administration
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die();
+}
+
 $action = ! empty( $_REQUEST['action'] ) ? sanitize_text_field( $_REQUEST['action'] ) : '';
 
 if ( isset( $_GET['updated'] ) && isset( $_GET['page'] ) ) {
diff --git a/src/wp-admin/user/menu.php b/src/wp-admin/user/menu.php
index 23e81a892c273..587d0ec1762dc 100644
--- a/src/wp-admin/user/menu.php
+++ b/src/wp-admin/user/menu.php
@@ -7,6 +7,11 @@
  * @since 3.1.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 $menu[2] = array( __( 'Dashboard' ), 'exist', 'index.php', '', 'menu-top menu-top-first menu-icon-dashboard', 'menu-dashboard', 'dashicons-dashboard' );
 
 $menu[4] = array( '', 'exist', 'separator1', '', 'wp-menu-separator' );
diff --git a/src/wp-includes/class-IXR.php b/src/wp-includes/class-IXR.php
index 0cd72df20e895..35657c7c7378f 100644
--- a/src/wp-includes/class-IXR.php
+++ b/src/wp-includes/class-IXR.php
@@ -39,6 +39,11 @@
  * @license    http://www.opensource.org/licenses/bsd-license.php BSD
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 require_once ABSPATH . WPINC . '/IXR/class-IXR-server.php';
 
 require_once ABSPATH . WPINC . '/IXR/class-IXR-base64.php';
diff --git a/src/wp-includes/class-wp-customize-control.php b/src/wp-includes/class-wp-customize-control.php
index 596c6e3723c8e..1108c94106d6f 100644
--- a/src/wp-includes/class-wp-customize-control.php
+++ b/src/wp-includes/class-wp-customize-control.php
@@ -7,6 +7,11 @@
  * @since 3.4.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /**
  * Customize Control class.
  *
diff --git a/src/wp-includes/class-wp-customize-panel.php b/src/wp-includes/class-wp-customize-panel.php
index 95b7aed468814..d1dc386d31b98 100644
--- a/src/wp-includes/class-wp-customize-panel.php
+++ b/src/wp-includes/class-wp-customize-panel.php
@@ -7,6 +7,11 @@
  * @since 4.0.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /**
  * Customize Panel class.
  *
diff --git a/src/wp-includes/class-wp-customize-setting.php b/src/wp-includes/class-wp-customize-setting.php
index 99d0d2e51f199..95f6b26972682 100644
--- a/src/wp-includes/class-wp-customize-setting.php
+++ b/src/wp-includes/class-wp-customize-setting.php
@@ -7,6 +7,11 @@
  * @since 3.4.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /**
  * Customize Setting class.
  *
diff --git a/src/wp-includes/class-wp-http.php b/src/wp-includes/class-wp-http.php
index ea8adde0ba7c7..9e912858a0efc 100644
--- a/src/wp-includes/class-wp-http.php
+++ b/src/wp-includes/class-wp-http.php
@@ -7,6 +7,11 @@
  * @since 2.7.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 if ( ! class_exists( 'WpOrg\Requests\Autoload' ) ) {
 	require ABSPATH . WPINC . '/Requests/src/Autoload.php';
 
diff --git a/src/wp-includes/class-wp-simplepie-sanitize-kses.php b/src/wp-includes/class-wp-simplepie-sanitize-kses.php
index c300cf2280762..c644b1748fcb5 100644
--- a/src/wp-includes/class-wp-simplepie-sanitize-kses.php
+++ b/src/wp-includes/class-wp-simplepie-sanitize-kses.php
@@ -7,6 +7,11 @@
  * @since 4.7.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /**
  * Core class used to implement SimplePie feed sanitization.
  *
diff --git a/src/wp-includes/class-wp-text-diff-renderer-table.php b/src/wp-includes/class-wp-text-diff-renderer-table.php
index 4fa3d414d2401..25272265e261b 100644
--- a/src/wp-includes/class-wp-text-diff-renderer-table.php
+++ b/src/wp-includes/class-wp-text-diff-renderer-table.php
@@ -7,6 +7,11 @@
  * @since 4.7.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /**
  * Table renderer to display the diff lines.
  *
diff --git a/src/wp-includes/default-filters.php b/src/wp-includes/default-filters.php
index 1bcd85e79aaf5..cfe5a6bd5fc6f 100644
--- a/src/wp-includes/default-filters.php
+++ b/src/wp-includes/default-filters.php
@@ -17,6 +17,11 @@
  * @package WordPress
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 // Strip, trim, kses, special chars for string saves.
 foreach ( array( 'pre_term_name', 'pre_comment_author_name', 'pre_link_name', 'pre_link_target', 'pre_link_rel', 'pre_user_display_name', 'pre_user_first_name', 'pre_user_last_name', 'pre_user_nickname' ) as $filter ) {
 	add_filter( $filter, 'sanitize_text_field' );
diff --git a/src/wp-includes/default-widgets.php b/src/wp-includes/default-widgets.php
index f8f3c4d141535..cbb25de8f0a4e 100644
--- a/src/wp-includes/default-widgets.php
+++ b/src/wp-includes/default-widgets.php
@@ -7,6 +7,11 @@
  * @since 2.8.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /** WP_Widget_Pages class */
 require_once ABSPATH . WPINC . '/widgets/class-wp-widget-pages.php';
 
diff --git a/src/wp-includes/feed-atom.php b/src/wp-includes/feed-atom.php
index e9e3f49528065..9ee70f895a4c9 100644
--- a/src/wp-includes/feed-atom.php
+++ b/src/wp-includes/feed-atom.php
@@ -5,6 +5,11 @@
  * @package WordPress
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 header( 'Content-Type: ' . feed_content_type( 'atom' ) . '; charset=' . get_option( 'blog_charset' ), true );
 $more = 1;
 
diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 6e6f085d3454f..b2661962cefc0 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -5,6 +5,11 @@
  * @package WordPress
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 require ABSPATH . WPINC . '/option.php';
 
 /**
diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 0a8621d209815..e3474bbeb4ccf 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -6,6 +6,10 @@
  * @subpackage Media
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
 /**
  * Retrieves additional image sizes.
  *
diff --git a/src/wp-includes/ms-blogs.php b/src/wp-includes/ms-blogs.php
index 2cf6d2390aab7..ae642282d097c 100644
--- a/src/wp-includes/ms-blogs.php
+++ b/src/wp-includes/ms-blogs.php
@@ -8,6 +8,11 @@
  * @since MU (3.0.0)
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 require_once ABSPATH . WPINC . '/ms-site.php';
 require_once ABSPATH . WPINC . '/ms-network.php';
 
diff --git a/src/wp-includes/ms-settings.php b/src/wp-includes/ms-settings.php
index 27dc1337f5fd0..c665da17e3aeb 100644
--- a/src/wp-includes/ms-settings.php
+++ b/src/wp-includes/ms-settings.php
@@ -10,6 +10,11 @@
  * @since 3.0.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /**
  * Objects representing the current network and current site.
  *
diff --git a/src/wp-includes/nav-menu-template.php b/src/wp-includes/nav-menu-template.php
index 860efa92d3377..d90fdfa8061ab 100644
--- a/src/wp-includes/nav-menu-template.php
+++ b/src/wp-includes/nav-menu-template.php
@@ -7,6 +7,11 @@
  * @since 3.0.0
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 /** Walker_Nav_Menu class */
 require_once ABSPATH . WPINC . '/class-walker-nav-menu.php';
 
diff --git a/src/wp-includes/update.php b/src/wp-includes/update.php
index e2ac6b8b54dbc..2b748404a4652 100644
--- a/src/wp-includes/update.php
+++ b/src/wp-includes/update.php
@@ -24,6 +24,12 @@
  * @param bool  $force_check Whether to bypass the transient cache and force a fresh update check.
  *                           Defaults to false, true if $extra_stats is set.
  */
+
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 function wp_version_check( $extra_stats = array(), $force_check = false ) {
 	global $wpdb, $wp_local_package;
 
diff --git a/src/wp-includes/vars.php b/src/wp-includes/vars.php
index b719b48d2e87f..22496330c33ff 100644
--- a/src/wp-includes/vars.php
+++ b/src/wp-includes/vars.php
@@ -15,6 +15,11 @@
  * @package WordPress
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 global $pagenow,
 	$is_lynx, $is_gecko, $is_winIE, $is_macIE, $is_opera, $is_NS4, $is_safari, $is_chrome, $is_iphone, $is_IE, $is_edge,
 	$is_apache, $is_IIS, $is_iis7, $is_nginx, $is_caddy;
diff --git a/src/wp-includes/wp-diff.php b/src/wp-includes/wp-diff.php
index 235b04b4bed08..24b0bb41a44a5 100644
--- a/src/wp-includes/wp-diff.php
+++ b/src/wp-includes/wp-diff.php
@@ -8,6 +8,11 @@
  * @subpackage Diff
  */
 
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
 if ( ! class_exists( 'Text_Diff', false ) ) {
 	/** Text_Diff class */
 	require ABSPATH . WPINC . '/Text/Diff.php';