本篇内容主要讲解“怎么滥用IBM WebSphere平台中的Java远程协议漏洞”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“怎么滥用IBM WebSphere平台中的Java远程协议漏洞”吧!
CORBA，即公共对象请求代理体系结构，它是一个由对象管理组织（OMG）定义的标准化规范。它是一个独立与平台的RPC框架，并且早于SOAP和gRPC等标准出现。在分布式环境中，CORBA使用了互联网InterORB协议（IIOP）来实现端点之间的通信。在IBM WebSphere的默认安装配置下，CORBA服务可以运行在TCP端口2809、9100、9402和9403。在调用服务方法之前，Interceptor类将会拦截调用请求，这里我们需要注意的是TxServerInterceptor类。
CVE-2020-4450-snippet-1.java：
public void receive_request(ServerRequestInfo sri) {
// ...snip...
if (TxProperties.SINGLE_PROCESS) {
propagationContext = TxInterceptorHelper.demarshalContext(serviceContext.context_data, (ORB)((LocalObject)sri)._orb()); // <------------
contextType = TxInterceptorHelper.determineContextType(propagationContext);
}
// ...snip...
}
public static final PropagationContext demarshalContext(byte[] bytes, ORB orb) {
// ...snip...
propContext.implementation_specific_data = inputStream.read_any(); // <-------
// ...snip...
}
public Any read_any() {
// ...snip...
any.read_value(this.encoderStream, typeCodeImpl); // <------------------------
return any;
}
private Object simpleReadObjectInternal(Class paramClass, String paramString) throws ClassNotFoundException, IOException {
// ...snip...
return readSerializable(paramClass, objectStreamClass, paramString); // <------
// ...snip...
}
private Object readSerializable(Class paramClass, ObjectStreamClass paramObjectStreamClass, String paramString) throws IOException, ClassNotFoundException {
// ...snip...
return inputObjectClassDesc(serializable, paramObjectStreamClass); // <-------
}
private Object inputObjectClassDesc(Object paramObject, ObjectStreamClass paramObjectStreamClass) throws IOException, ClassNotFoundException {
ObjectStreamClass objectStreamClass = processClassHierarchy(paramObject, paramObjectStreamClass);
return inputObjectUsingClassDesc(paramObject, objectStreamClass); // <--------
}
Object inputObjectUsingClassDesc(Object paramObject, ObjectStreamClass paramObjectStreamClass) throws IOException, ClassNotFoundException {
// ...snip...
ObjectStreamClass objectStreamClass = this.readObjectOSC;
this.readObjectOSC = paramObjectStreamClass;
paramObjectStreamClass.readObjectMethod.invoke(paramObject, this.readObjectArglist); // <--- calls readObject()
this.readObjectOSC = objectStreamClass;
return true;
}
当TxServerInterceptor类成功拦截调用请求时，便会调用receive_request()方法，同时还会试用demarshalContext()方法来从字节流中接收一个ServiceContext对象，而这个对象是攻击者可控的。任何嵌入在这个字节流中的对象都可以通过调用read_any()方法来提取，最终通过调用readObject()方法来获取嵌入的对象类。
远程代码执行漏洞（CVE-2020-4450）
尽管我们可以实现对任何对象进行反序列化操作，但实现远程代码执行并非易事。这是因为IBM Java SDK实现了针对反序列化攻击的安全缓解措施，其中包括：
-
拥有更严格的ClassLoader类，在运行时仅提供必要的类；
-
TemplatesImpl类已无法再被序列化；
-
IBM SDK不会使用Oracle JDK的Java名命方法以及目录接口（JNDI）。因此，我们无法通过RMI/LDAP来加载远程类并实现漏洞利用；
根据tint0的描述，tint0提供了一个Gadget链来绕过这种缓解方案。这个Gadget使用了WSIFPort_EJB类作为入口点。
CVE-2020-4450-snippet-2.java：
public class WSIFPort_EJB
extends WSIFDefaultPort
implements Serializable
{
// ...snip...
private void readObject(ObjectInputStream ois) throws ClassNotFoundException, IOException {
ois.defaultReadObject();
if (this.separatedEJBRefs) {
Object objHome = ois.readObject();
if (objHome != null && objHome instanceof HomeHandle) {
HomeHandle homeHandle = (HomeHandle)objHome;
this.fieldEjbHome = homeHandle.getEJBHome();
}
Object obj = ois.readObject();
if (obj != null && obj instanceof Handle) {
Handle handle = (Handle)obj;
this.fieldEjbObject = handle.getEJBObject(); // <----------------------
}
}
}
}
public EJBObject getEJBObject() throws RemoteException {
// ...snip...
home = (EJBHome)PortableRemoteObject.narrow(ctx.lookup(this.homeJNDIName), homeClass); // <----
// ...snip...
Method fbpk = findFindByPrimaryKey(homeClass); // <---- returns findFindByPrimaryKey() method
this.object = (EJBObject)fbpk.invoke(home, new Object[] { this.key }); <-- $proxy.findFindByPrimaryKey(Serializable $arg)
}
这个类最有趣的地方在于getEJBObject()方法，我们一起来看一看这里面的JNDI查询调用。
CVE-2020-4450-snippet-3.java：
com.sun.jndi.rmi.registry.RegistryContext#lookup
com.sun.jndi.rmi.registry.RegistryContext#decodeObject
javax.naming.spi.NamingManager#getObjectInstance
org.apache.aries.jndi.OSGiObjectFactoryBuilder#getObjectInstance
org.apache.aries.jndi.ObjectFactoryHelper#getObjectInstance
org.apache.aries.jndi.ObjectFactoryHelper#getObjectInstanceViaContextDotObjectFactories
protected Object getObjectInstanceViaContextDotObjectFactories(Object obj, Name name, Context nameCtx, Hashtable<?, ?> environment, Attributes attrs) throws Exception {
Object result = null;
String factories = (String)environment.get("java.naming.factory.object");
if (factories != null && factories.length() > 0) {
String[] candidates = factories.split(":");
ClassLoader cl = (ClassLoader)AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
public ClassLoader run() {
return Thread.currentThread().getContextClassLoader();
}
});
for (String cand : candidates) {
ObjectFactory factory = null;
try {
Class<ObjectFactory> clz = cl.loadClass(cand);
factory = (ObjectFactory)clz.newInstance();
} catch (Exception e) {
if (logger.isLoggable(Level.FINE)) logger.log(Level.FINE, "Exception instantiating factory: " + e);
}
if (logger.isLoggable(Level.FINE)) logger.log(Level.FINE, "cand=" + cand + " factory=" + factory);
if (factory != null) {
if (factory instanceof DirObjectFactory) {
if (logger.isLoggable(Level.FINE)) logger.log(Level.FINE, "its a DirObjectFactory");
DirObjectFactory dirFactory = (DirObjectFactory)factory;
result = dirFactory.getObjectInstance(obj, name, nameCtx, environment, attrs);
}
else {
if (logger.isLoggable(Level.FINE)) logger.log(Level.FINE, "its an ObjectFactory");
result = factory.getObjectInstance(obj, name, nameCtx, environment);
}
}
if (result != null && result != obj)
break;
}
} if (logger.isLoggable(Level.FINE)) logger.log(Level.FINE, "result = " + result);
return (result == null) ? obj : result;
}
我们可以看到，getObjectInstanceViaContextDotObjectFactories()将会调用getObjectInstance的任意ObjectFactory类，其中一个跟我们Gadget链相关的类就是WSIFServiceObjectFactory。
CVE-2020-4450-snippet-4.java：
public Object getObjectInstance(Object obj, Name name, Context context, Hashtable env) throws Exception {
Trc.entry(this, obj, name, context, env);
if (obj instanceof Reference && obj != null) {
Reference ref = (Reference)obj;
if (ref.getClassName().equals(WSIFServiceRef.class.getName())) {
String wsdlLoc = resolveString(ref.get("wsdlLoc"));
String serviceNS = resolveString(ref.get("serviceNS"));
String serviceName = resolveString(ref.get("serviceName"));
String portTypeNS = resolveString(ref.get("portTypeNS"));
String portTypeName = resolveString(ref.get("portTypeName"));
if (wsdlLoc != null) {
WSIFServiceFactory factory = WSIFServiceFactory.newInstance();
WSIFService service = factory.getService(wsdlLoc, serviceNS, serviceName, portTypeNS, portTypeName);
Trc.exit(service);
return service;
}
} else if (ref.getClassName().equals(WSIFServiceStubRef.class.getName())) {
String wsdlLoc = resolveString(ref.get("wsdlLoc"));
String serviceNS = resolveString(ref.get("serviceNS"));
String serviceName = resolveString(ref.get("serviceName"));
String portTypeNS = resolveString(ref.get("portTypeNS"));
String portTypeName = resolveString(ref.get("portTypeName"));
String preferredPort = resolveString(ref.get("preferredPort"));
String className = resolveString(ref.get("className"));
if (wsdlLoc != null) {
WSIFServiceFactory factory = WSIFServiceFactory.newInstance();
WSIFService service = factory.getService(wsdlLoc, serviceNS, serviceName, portTypeNS, portTypeName); // <----
Class iface = Class.forName(className, true, Thread.currentThread().getContextClassLoader());
Object stub = service.getStub(preferredPort, iface);
Trc.exit(stub);
return stub;
}
}
}
}
针对getObjectInstance()的调用将会根据一个指向远程XML定义的URL来初始化一个Web服务调用框架（WSIF）服务，而这个XML也是攻击者可控的。在这种场景下，服务的className会被设置为javax.el.ELProcessor，并且会定义一个java:operation元素，然后将findByPrimaryKey()映射为eval()方法。
getObjectInstance()调用将会返回一个WSIFClientProxy Java代理对象，当findByPrimaryKey()方法被调用时，这个代理对象将会调用ELProcessor实例的eval()方法。别忘了我们已经可以通过反序列化来控制this.key参数了，那么这样一来，我们就可以通过表达式语言注入技术来实现远程代码执行了。
信息披露漏洞（CVE-2020-4449）
这个漏洞利用Gadget利用的是一个XXE漏洞，漏洞代码如下所示。
CVE-2020-4450-snippet-5.java：
public static Definition readWSDL(String contextURL, String wsdlLoc) throws WSDLException {
Trc.entry(null, contextURL, wsdlLoc);
initializeProviders();
WSDLFactory factory = WSDLFactory.newInstance("org.apache.wsif.wsdl.WSIFWSDLFactoryImpl");
WSDLReader wsdlReader = factory.newWSDLReader(); // <---------------------
wsdlReader.setFeature("javax.wsdl.verbose", false);
try {
Definition def = wsdlReader.readWSDL(contextURL, wsdlLoc); // <---------
Trc.exitExpandWsdl(def);
return def;
} catch (WSDLException e) {
Trc.exception(e);
MessageLogger.log("WSIF.0002E", wsdlLoc);
throw e;
}
}
这个Gadget还演示了如何在现代JRE中如何绕过类似的缓解方案，尤其是通过FTP来实现越界提取等等。在这种场景下，数据是通过错误信息来提取的，因此当代码在解析XML文档时，如果没有封装在一个try/catch语句中的话，那么该漏洞将产生严重影响。
漏洞修复
为了修复这些漏洞，IBM采取了很多措施来确保TxServerInterceptor类不再会被反序列化为任意对象：
到此，相信大家对“怎么滥用IBM WebSphere平台中的Java远程协议漏洞”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
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