diff --git a/wp-includes/blocks.php b/wp-includes/blocks.php
index 854992de57..5b452c69c4 100644
--- a/wp-includes/blocks.php
+++ b/wp-includes/blocks.php
@@ -1447,7 +1447,7 @@ function _filter_block_content_callback( $matches ) {
  * @return array The filtered and sanitized block object result.
  */
 function filter_block_kses( $block, $allowed_html, $allowed_protocols = array() ) {
-	$block['attrs'] = filter_block_kses_value( $block['attrs'], $allowed_html, $allowed_protocols );
+	$block['attrs'] = filter_block_kses_value( $block['attrs'], $allowed_html, $allowed_protocols, $block );
 
 	if ( is_array( $block['innerBlocks'] ) ) {
 		foreach ( $block['innerBlocks'] as $i => $inner_block ) {
@@ -1463,6 +1463,7 @@ function filter_block_kses( $block, $allowed_html, $allowed_protocols = array()
  * non-allowable HTML.
  *
  * @since 5.3.1
+ * @since 6.5.5 Added the `$block_context` parameter.
  *
  * @param string[]|string $value             The attribute value to filter.
  * @param array[]|string  $allowed_html      An array of allowed HTML elements and attributes,
@@ -1470,13 +1471,18 @@ function filter_block_kses( $block, $allowed_html, $allowed_protocols = array()
  *                                           for the list of accepted context names.
  * @param string[]        $allowed_protocols Optional. Array of allowed URL protocols.
  *                                           Defaults to the result of wp_allowed_protocols().
+ * @param array           $block_context     Optional. The block the attribute belongs to, in parsed block array format.
  * @return string[]|string The filtered and sanitized result.
  */
-function filter_block_kses_value( $value, $allowed_html, $allowed_protocols = array() ) {
+function filter_block_kses_value( $value, $allowed_html, $allowed_protocols = array(), $block_context = null ) {
 	if ( is_array( $value ) ) {
 		foreach ( $value as $key => $inner_value ) {
-			$filtered_key   = filter_block_kses_value( $key, $allowed_html, $allowed_protocols );
-			$filtered_value = filter_block_kses_value( $inner_value, $allowed_html, $allowed_protocols );
+			$filtered_key   = filter_block_kses_value( $key, $allowed_html, $allowed_protocols, $block_context );
+			$filtered_value = filter_block_kses_value( $inner_value, $allowed_html, $allowed_protocols, $block_context );
+
+			if ( isset( $block_context['blockName'] ) && 'core/template-part' === $block_context['blockName'] ) {
+				$filtered_value = filter_block_core_template_part_attributes( $filtered_value, $filtered_key, $allowed_html );
+			}
 
 			if ( $filtered_key !== $key ) {
 				unset( $value[ $key ] );
@@ -1491,6 +1497,28 @@ function filter_block_kses_value( $value, $allowed_html, $allowed_protocols = ar
 	return $value;
 }
 
+/**
+ * Sanitizes the value of the Template Part block's `tagName` attribute.
+ *
+ * @since 6.5.5
+ *
+ * @param string          $attribute_value   The attribute value to filter.
+ * @param string          $attribute_name    The attribute name.
+ * @param array[]|string  $allowed_html      An array of allowed HTML elements and attributes,
+ *                                           or a context name such as 'post'. See wp_kses_allowed_html()
+ *                                           for the list of accepted context names.
+ * @return string The sanitized attribute value.
+ */
+function filter_block_core_template_part_attributes( $attribute_value, $attribute_name, $allowed_html ) {
+	if ( empty( $attribute_value ) || 'tagName' !== $attribute_name ) {
+		return $attribute_value;
+	}
+	if ( ! is_array( $allowed_html ) ) {
+		$allowed_html = wp_kses_allowed_html( $allowed_html );
+	}
+	return isset( $allowed_html[ $attribute_value ] ) ? $attribute_value : '';
+}
+
 /**
  * Parses blocks out of a content string, and renders those appropriate for the excerpt.
  *
diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index a756f6d12a..b097d000ef 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -4802,12 +4802,13 @@ EOF;
  * Escapes an HTML tag name.
  *
  * @since 2.5.0
+ * @since 6.5.5 Allow hyphens in tag names (i.e. custom elements).
  *
  * @param string $tag_name
  * @return string
  */
 function tag_escape( $tag_name ) {
-	$safe_tag = strtolower( preg_replace( '/[^a-zA-Z0-9_:]/', '', $tag_name ) );
+	$safe_tag = strtolower( preg_replace( '/[^a-zA-Z0-9-_:]/', '', $tag_name ) );
 	/**
 	 * Filters a string cleaned and escaped for output as an HTML tag.
 	 *
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index fd305be20b..f9d617660a 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -6192,6 +6192,9 @@ function validate_file( $file, $allowed_files = array() ) {
 		return 0;
 	}
 
+	// Normalize path for Windows servers
+	$file = wp_normalize_path( $file );
+
 	// `../` on its own is not allowed:
 	if ( '../' === $file ) {
 		return 1;
diff --git a/wp-includes/html-api/class-wp-html-tag-processor.php b/wp-includes/html-api/class-wp-html-tag-processor.php
index c540ea96c1..bf7e026bce 100644
--- a/wp-includes/html-api/class-wp-html-tag-processor.php
+++ b/wp-includes/html-api/class-wp-html-tag-processor.php
@@ -2968,7 +2968,14 @@ class WP_HTML_Tag_Processor {
 		if ( true === $value ) {
 			$updated_attribute = $name;
 		} else {
-			$escaped_new_value = esc_attr( $value );
+			$comparable_name = strtolower( $name );
+
+			/*
+			 * Escape URL attributes.
+			 *
+			 * @see https://html.spec.whatwg.org/#attributes-3
+			 */
+			$escaped_new_value = in_array( $comparable_name, wp_kses_uri_attributes() ) ? esc_url( $value ) : esc_attr( $value );
 			$updated_attribute = "{$name}=\"{$escaped_new_value}\"";
 		}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 61f4db61d7..d43cecce57 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.5.5-alpha-58448';
+$wp_version = '6.5.5-alpha-58474';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.