diff --git a/core/lib/Drupal/Component/Utility/Xss.php b/core/lib/Drupal/Component/Utility/Xss.php
index 2078e4b..468b544 100644
--- a/core/lib/Drupal/Component/Utility/Xss.php
+++ b/core/lib/Drupal/Component/Utility/Xss.php
@@ -276,12 +276,7 @@ protected static function attributes($attributes) {
         case 2:
           // Attribute value, a URL after href= for instance.
           if (preg_match('/^"([^"]*)"(\s+|$)/', $attributes, $match)) {
-            if (in_array($attribute_name, static::$rdfaAttributes)) {
-              $thisval = ($skip_protocol_filtering || preg_match('/^[[:alnum:]]+\:[[:alnum:]]+$/', $match[1])) ? $match[1] : UrlHelper::filterBadProtocol($match[1]);
-            }
-            else {
-              $thisval = $skip_protocol_filtering ? $match[1] : UrlHelper::filterBadProtocol($match[1]);
-            }
+            $thisval = $skip_protocol_filtering ? $match[1] : static::filterProtocol($attribute_name, $match[1]);
 
             if (!$skip) {
               $attributes_array[] = "$attribute_name=\"$thisval\"";
@@ -293,12 +288,7 @@ protected static function attributes($attributes) {
           }
 
           if (preg_match("/^'([^']*)'(\s+|$)/", $attributes, $match)) {
-            if (in_array($attribute_name, static::$rdfaAttributes)) {
-              $thisval = ($skip_protocol_filtering || preg_match('/^[[:alnum:]]+\:[[:alnum:]]+$/', $match[1])) ? $match[1] : UrlHelper::filterBadProtocol($match[1]);
-            }
-            else {
-              $thisval = $skip_protocol_filtering ? $match[1] : UrlHelper::filterBadProtocol($match[1]);
-            }
+            $thisval = $skip_protocol_filtering ? $match[1] : static::filterProtocol($attribute_name, $match[1]);
 
             if (!$skip) {
               $attributes_array[] = "$attribute_name='$thisval'";
@@ -309,12 +299,7 @@ protected static function attributes($attributes) {
           }
 
           if (preg_match("%^([^\s\"']+)(\s+|$)%", $attributes, $match)) {
-            if (in_array($attribute_name, static::$rdfaAttributes)) {
-              $thisval = ($skip_protocol_filtering || preg_match('/^[[:alnum:]]+\:[[:alnum:]]+$/', $match[1])) ? $match[1] : UrlHelper::filterBadProtocol($match[1]);
-            }
-            else {
-              $thisval = $skip_protocol_filtering ? $match[1] : UrlHelper::filterBadProtocol($match[1]);
-            }
+            $thisval = $skip_protocol_filtering ? $match[1] : static::filterProtocol($attribute_name, $match[1]);
 
             if (!$skip) {
               $attributes_array[] = "$attribute_name=\"$thisval\"";
@@ -350,6 +335,28 @@ protected static function attributes($attributes) {
   }
 
   /**
+   * Strips bad protocols from attribute values.
+   *
+   * @param string $name
+   *   The attribute name.
+   * @param string $value
+   *   The attribute value.
+   *
+   * @return string
+   *   The attribute value, stripped of any bad protocols.
+   */
+  protected static function filterProtocol($name, $value) {
+    // If the value matches the typical namespace:value pattern used in RDFa,
+    // return it directly. Otherwise, filter it.
+    if (in_array($name, static::$rdfaAttributes)) {
+      return preg_match('/^[[:alnum:]]+\:[[:alnum:]]+$/', $value) ? $value : UrlHelper::filterBadProtocol($value);
+    }
+    else {
+      return UrlHelper::filterBadProtocol($value);
+    }
+  }
+
+  /**
    * Whether this element needs to be removed altogether.
    *
    * @param $html_tags