diff --git a/core/src/main/java/hudson/ClassicPluginStrategy.java b/core/src/main/java/hudson/ClassicPluginStrategy.java
index 1047ec5a3dbc..10b0d179fdd7 100644
--- a/core/src/main/java/hudson/ClassicPluginStrategy.java
+++ b/core/src/main/java/hudson/ClassicPluginStrategy.java
@@ -86,11 +86,6 @@ public class ClassicPluginStrategy implements PluginStrategy {
 
     private final PluginManager pluginManager;
 
-    /**
-     * All the plugins eventually delegate this classloader to load core, servlet APIs, and SE runtime.
-     */
-    private final MaskingClassLoader coreClassLoader = new MaskingClassLoader(getClass().getClassLoader());
-
     public ClassicPluginStrategy(PluginManager pluginManager) {
         this.pluginManager = pluginManager;
     }
@@ -235,16 +230,8 @@ private static Manifest loadLinkedManifest(File archive) throws IOException {
 
         fix(atts, optionalDependencies);
 
-        // Register global classpath mask. This is useful for hiding JavaEE APIs that you might see from the container,
-        // such as database plugin for JPA support. The Mask-Classes attribute is insufficient because those classes
-        // also need to be masked by all the other plugins that depend on the database plugin.
-        String masked = atts.getValue("Global-Mask-Classes");
-        if (masked != null) {
-            for (String pkg : masked.trim().split("[ \t\r\n]+"))
-                coreClassLoader.add(pkg);
-        }
-
-        ClassLoader dependencyLoader = new DependencyClassLoader(coreClassLoader, archive, Util.join(dependencies, optionalDependencies), pluginManager);
+        ClassLoader dependencyLoader = new DependencyClassLoader(
+                getClass().getClassLoader(), archive, Util.join(dependencies, optionalDependencies), pluginManager);
         dependencyLoader = getBaseClassLoader(atts, dependencyLoader);
 
         return new PluginWrapper(pluginManager, archive, manifest, baseResourceURL,
diff --git a/core/src/main/java/hudson/util/MaskingClassLoader.java b/core/src/main/java/hudson/util/MaskingClassLoader.java
index efb05831ccce..74bbbe1a9863 100644
--- a/core/src/main/java/hudson/util/MaskingClassLoader.java
+++ b/core/src/main/java/hudson/util/MaskingClassLoader.java
@@ -31,7 +31,7 @@
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.List;
-import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.stream.Collectors;
 
 /**
  * {@link ClassLoader} that masks a specified set of classes
@@ -46,9 +46,9 @@ public class MaskingClassLoader extends ClassLoader {
     /**
      * Prefix of the packages that should be hidden.
      */
-    private final List<String> masksClasses = new CopyOnWriteArrayList<>();
+    private final List<String> masksClasses;
 
-    private final List<String> masksResources = new CopyOnWriteArrayList<>();
+    private final List<String> masksResources;
 
     static {
         registerAsParallelCapable();
@@ -60,14 +60,13 @@ public MaskingClassLoader(ClassLoader parent, String... masks) {
 
     public MaskingClassLoader(ClassLoader parent, Collection<String> masks) {
         super(parent);
-        this.masksClasses.addAll(masks);
+        this.masksClasses = List.copyOf(masks);
 
         /*
          * The name of a resource is a '/'-separated path name
          */
-        for (String mask : masks) {
-            masksResources.add(mask.replace('.', '/'));
-        }
+        this.masksResources =
+                masks.stream().map(mask -> mask.replace('.', '/')).collect(Collectors.toUnmodifiableList());
     }
 
     @Override
@@ -94,13 +93,6 @@ public Enumeration<URL> getResources(String name) throws IOException {
         return super.getResources(name);
     }
 
-    public void add(String prefix) {
-        masksClasses.add(prefix);
-        if (prefix != null) {
-            masksResources.add(prefix.replace('.', '/'));
-        }
-    }
-
     private boolean isMasked(String name) {
         for (String mask : masksResources) {
             if (name.startsWith(mask))