From a20cb28d147b7090175c10a5f6ed6fdc49f347d2 Mon Sep 17 00:00:00 2001
From: Weston Ruter <weston@xwp.co>
Date: Fri, 29 Sep 2023 19:47:21 +0000
Subject: [PATCH] Script Loader: Harden removal of script tag wrappers.

* Add `wp_remove_surrounding_empty_script_tags()` to more precisely remove script tag wrappers and warn when doing it wrong.
* Add clarifying comments for XML escaping logic in `wp_get_inline_script_tag()`.
* Leverage `WP_HTML_Tag_Processor` in `test_remove_frameless_preview_messenger_channel`.
* Reuse `assertEqualMarkup` in `test_blocking_dependent_with_delayed_dependency`.
* Normalize whitespace in `parse_markup_fragment` for `assertEqualMarkup`.

Follow-up to [56687].
Props dmsnell, westonruter, flixos90.
See #58664.

Built from https://develop.svn.wordpress.org/trunk@56748


git-svn-id: http://core.svn.wordpress.org/trunk@56260 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/class-wp-customize-manager.php    |  8 +-
 wp-includes/functions.php                     |  2 +-
 wp-includes/script-loader.php                 | 86 ++++++++++++++++++-
 wp-includes/theme-templates.php               |  2 +-
 wp-includes/theme.php                         |  2 +-
 wp-includes/version.php                       |  2 +-
 .../widgets/class-wp-widget-archives.php      |  2 +-
 .../widgets/class-wp-widget-categories.php    |  2 +-
 wp-login.php                                  | 10 +--
 9 files changed, 99 insertions(+), 17 deletions(-)

diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index aebcfeb892..c1cf81f142 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -474,7 +474,7 @@ final class WP_Customize_Manager {
 			} )( wp.customize, <?php echo wp_json_encode( $settings ); ?> );
 			</script>
 			<?php
-			$message .= wp_get_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+			$message .= wp_get_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 		}
 
 		wp_die( $message );
@@ -2109,7 +2109,7 @@ final class WP_Customize_Manager {
 		} )();
 		</script>
 		<?php
-		wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+		wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 	}
 
 	/**
@@ -2230,7 +2230,7 @@ final class WP_Customize_Manager {
 			})( _wpCustomizeSettings.values );
 		</script>
 		<?php
-		wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+		wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 	}
 
 	/**
@@ -5019,7 +5019,7 @@ final class WP_Customize_Manager {
 			?>
 		</script>
 		<?php
-		wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+		wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 	}
 
 	/**
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index d7c0a9bbdf..d070c1695a 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -7619,7 +7619,7 @@ function wp_post_preview_js() {
 	}());
 	</script>
 	<?php
-	wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+	wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 }
 
 /**
diff --git a/wp-includes/script-loader.php b/wp-includes/script-loader.php
index 4f17461752..1527c69819 100644
--- a/wp-includes/script-loader.php
+++ b/wp-includes/script-loader.php
@@ -2853,9 +2853,43 @@ function wp_get_inline_script_tag( $javascript, $attributes = array() ) {
 		);
 	}
 
-	// Ensure markup is XHTML compatible if not HTML5.
+	/*
+	 * XHTML extracts the contents of the SCRIPT element and then the XML parser
+	 * decodes character references and other syntax elements. This can lead to
+	 * misinterpretation of the script contents or invalid XHTML documents.
+	 *
+	 * Wrapping the contents in a CDATA section instructs the XML parser not to
+	 * transform the contents of the SCRIPT element before passing them to the
+	 * JavaScript engine.
+	 *
+	 * Example:
+	 *
+	 *     <script>console.log('&hellip;');</script>
+	 *
+	 *     In an HTML document this would print "&hellip;" to the console,
+	 *     but in an XHTML document it would print "…" to the console.
+	 *
+	 *     <script>console.log('An image is <img> in HTML');</script>
+	 *
+	 *     In an HTML document this would print "An image is <img> in HTML",
+	 *     but it's an invalid XHTML document because it interprets the `<img>`
+	 *     as an empty tag missing its closing `/`.
+	 *
+	 * @see https://www.w3.org/TR/xhtml1/#h-4.8
+	 */
 	if ( ! $is_html5 ) {
-		$javascript = str_replace( ']]>', ']]]]><![CDATA[>', $javascript ); // Escape any existing CDATA section.
+		/*
+		 * If the string `]]>` exists within the JavaScript it would break
+		 * out of any wrapping CDATA section added here, so to start, it's
+		 * necessary to escape that sequence which requires splitting the
+		 * content into two CDATA sections wherever it's found.
+		 *
+		 * Note: it's only necessary to escape the closing `]]>` because
+		 * an additional `<![CDATA[` leaves the contents unchanged.
+		 */
+		$javascript = str_replace( ']]>', ']]]]><![CDATA[>', $javascript );
+
+		// Wrap the entire escaped script inside a CDATA section.
 		$javascript = sprintf( "/* <![CDATA[ */\n%s\n/* ]]> */", $javascript );
 	}
 
@@ -3299,3 +3333,51 @@ function wp_add_editor_classic_theme_styles( $editor_settings ) {
 
 	return $editor_settings;
 }
+
+/**
+ * Removes leading and trailing _empty_ script tags.
+ *
+ * This is a helper meant to be used for literal script tag construction
+ * within `wp_get_inline_script_tag()` or `wp_print_inline_script_tag()`.
+ * It removes the literal values of "<script>" and "</script>" from
+ * around an inline script after trimming whitespace. Typlically this
+ * is used in conjunction with output buffering, where `ob_get_clean()`
+ * is passed as the `$contents` argument.
+ *
+ * Example:
+ *
+ *     // Strips exact literal empty SCRIPT tags.
+ *     $js = '<script>sayHello();</script>;
+ *     'sayHello();' === wp_remove_surrounding_empty_script_tags( $js );
+ *
+ *     // Otherwise if anything is different it warns in the JS console.
+ *     $js = '<script type="text/javascript">console.log( "hi" );</script>';
+ *     'console.error( ... )' === wp_remove_surrounding_empty_script_tags( $js );
+ *
+ * @private
+ * @since 6.4.0
+ *
+ * @see wp_print_inline_script_tag()
+ * @see wp_get_inline_script_tag()
+ *
+ * @param string $contents Script body with manually created SCRIPT tag literals.
+ * @return string Script body without surrounding script tag literals, or
+ *                original contents if both exact literals aren't present.
+ */
+function wp_remove_surrounding_empty_script_tags( $contents ) {
+	$contents = trim( $contents );
+	$opener   = '<SCRIPT>';
+	$closer   = '</SCRIPT>';
+
+	if (
+		strlen( $contents ) > strlen( $opener ) + strlen( $closer ) &&
+		strtoupper( substr( $contents, 0, strlen( $opener ) ) ) === $opener &&
+		strtoupper( substr( $contents, -strlen( $closer ) ) ) === $closer
+	) {
+		return substr( $contents, strlen( $opener ), -strlen( $closer ) );
+	} else {
+		$error_message = __( 'Expected string to start with script tag (without attributes) and end with script tag, with optional whitespace.' );
+		_doing_it_wrong( __FUNCTION__, $error_message, '6.4' );
+		return sprintf( 'console.error(%s)', wp_json_encode( __( 'Function wp_remove_surrounding_empty_script_tags() used incorrectly in PHP.' ) . ' ' . $error_message ) );
+	}
+}
diff --git a/wp-includes/theme-templates.php b/wp-includes/theme-templates.php
index 8f0ee9a69f..cc4b19ecce 100644
--- a/wp-includes/theme-templates.php
+++ b/wp-includes/theme-templates.php
@@ -205,7 +205,7 @@ function the_block_template_skip_link() {
 	}() );
 	</script>
 	<?php
-	$skip_link_script = str_replace( array( '<script>', '</script>' ), '', ob_get_clean() );
+	$skip_link_script = wp_remove_surrounding_empty_script_tags( ob_get_clean() );
 	$script_handle    = 'wp-block-template-skip-link';
 	wp_register_script( $script_handle, false );
 	wp_add_inline_script( $script_handle, $skip_link_script );
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 087d563352..1eccd460b1 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -3800,7 +3800,7 @@ function wp_customize_support_script() {
 		}());
 	</script>
 	<?php
-	wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+	wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 }
 
 /**
diff --git a/wp-includes/version.php b/wp-includes/version.php
index cc38f4f2b6..f20a44fb47 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-beta1-56747';
+$wp_version = '6.4-beta1-56748';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-includes/widgets/class-wp-widget-archives.php b/wp-includes/widgets/class-wp-widget-archives.php
index 21d3a7b672..7457244833 100644
--- a/wp-includes/widgets/class-wp-widget-archives.php
+++ b/wp-includes/widgets/class-wp-widget-archives.php
@@ -120,7 +120,7 @@ class WP_Widget_Archives extends WP_Widget {
 })();
 </script>
 			<?php
-			wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+			wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 		} else {
 			$format = current_theme_supports( 'html5', 'navigation-widgets' ) ? 'html5' : 'xhtml';
 
diff --git a/wp-includes/widgets/class-wp-widget-categories.php b/wp-includes/widgets/class-wp-widget-categories.php
index e00ce7f960..b79881e752 100644
--- a/wp-includes/widgets/class-wp-widget-categories.php
+++ b/wp-includes/widgets/class-wp-widget-categories.php
@@ -108,7 +108,7 @@ class WP_Widget_Categories extends WP_Widget {
 </script>
 
 			<?php
-			wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+			wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 		} else {
 			$format = current_theme_supports( 'html5', 'navigation-widgets' ) ? 'html5' : 'xhtml';
 
diff --git a/wp-login.php b/wp-login.php
index 80887f0420..f03eea3636 100644
--- a/wp-login.php
+++ b/wp-login.php
@@ -105,7 +105,7 @@ function login_header( $title = 'Log In', $message = '', $wp_error = null ) {
 		?>
 		<script>if("sessionStorage" in window){try{for(var key in sessionStorage){if(key.indexOf("wp-autosave-")!=-1){sessionStorage.removeItem(key)}}}catch(e){}};</script>
 		<?php
-		wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+		wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 	}
 
 	/**
@@ -419,12 +419,12 @@ function login_footer( $input_id = '' ) {
 	if ( ! empty( $input_id ) ) {
 		ob_start();
 		?>
-		<script>
+		<script type="text/javascript">
 		try{document.getElementById('<?php echo $input_id; ?>').focus();}catch(e){}
 		if(typeof wpOnload==='function')wpOnload();
 		</script>
 		<?php
-		wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+		wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 	}
 
 	/**
@@ -1362,7 +1362,7 @@ switch ( $action ) {
 					?>
 					<script>setTimeout( function(){ new wp.customize.Messenger({ url: '<?php echo wp_customize_url(); ?>', channel: 'login' }).send('login') }, 1000 );</script>
 					<?php
-					wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+					wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 				}
 
 				?>
@@ -1627,7 +1627,7 @@ switch ( $action ) {
 			}());
 			</script>
 			<?php
-			wp_print_inline_script_tag( str_replace( array( '<script>', '</script>' ), '', ob_get_clean() ) );
+			wp_print_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
 		}
 
 		login_footer();