--- a/src/java/org/apache/velocity/runtime/defaults/velocity.properties
+++ b/src/java/org/apache/velocity/runtime/defaults/velocity.properties
@@ -245,15 +245,15 @@
 # accessed.
 # ----------------------------------------------------------------------------
 
+# Prohibit reflection
 introspector.restrict.packages = java.lang.reflect
 
-# The two most dangerous classes
+# ClassLoader, Thread, and subclasses disabled by default in SecureIntrospectorImpl
 
-introspector.restrict.classes = java.lang.Class
-introspector.restrict.classes = java.lang.ClassLoader
-                
-# Restrict these for extra safety
+# Restrict these system classes.  Note that anything in this list is matched exactly.
+# (Subclasses must be explicitly named to be included).
 
+introspector.restrict.classes = java.lang.Class
 introspector.restrict.classes = java.lang.Compiler
 introspector.restrict.classes = java.lang.InheritableThreadLocal
 introspector.restrict.classes = java.lang.Package
@@ -262,8 +262,15 @@
 introspector.restrict.classes = java.lang.RuntimePermission
 introspector.restrict.classes = java.lang.SecurityManager
 introspector.restrict.classes = java.lang.System
-introspector.restrict.classes = java.lang.Thread
 introspector.restrict.classes = java.lang.ThreadGroup
 introspector.restrict.classes = java.lang.ThreadLocal
 
+# Restrict instance managers for common servlet containers  (Tomcat, JBoss, Jetty)
+
+introspector.restrict.classes = org.apache.catalina.core.DefaultInstanceManager
+introspector.restrict.classes = org.apache.tomcat.SimpleInstanceManager
+introspector.restrict.classes = org.wildfly.extension.undertow.deployment.UndertowJSPInstanceManager
+introspector.restrict.classes = org.eclipse.jetty.util.DecoratedObjectFactory
+
+
 
--- a/src/java/org/apache/velocity/util/introspection/SecureIntrospectorImpl.java
+++ b/src/java/org/apache/velocity/util/introspection/SecureIntrospectorImpl.java
@@ -122,6 +122,15 @@
         }
 
         /**
+         * Always disallow ClassLoader, Thread and subclasses
+         */
+        if (ClassLoader.class.isAssignableFrom(clazz) ||
+            Thread.class.isAssignableFrom(clazz))
+        {
+           return false;
+        }
+
+        /**
          * check the classname (minus any array info)
          * whether it matches disallowed classes or packages
          */