【漏洞分析】Dubbo Pre-auth RCE（CVE-2021-30179）

#漏洞分析文章合集

2个

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作者：lz2y@Timeline Sec

本文字数：3220

阅读时长：8～10min

声明：仅供学习参考使用，请勿用作违法用途，否则后果自负

0x01 漏洞复现

《CVE-2021-30179：Apache Dubbo RCE复现》

0x02 调试准备

暂无

0x03 漏洞分析

Dubbo使用DecodeHandler#received方法来接收来自socket的连接，当接收到请求时会先调用DecodeHandler#decode方法处理请求，其将调用DecodeableRpcInvocation.java#decode方法处理数据

在138行通过方法名和desc获取服务端中的方法描述，如果为空则判断是否为泛类引用

判断方法名是否为$invoke或者$invokeAsync，desc是否为Ljava/lang/String;[Ljava/lang/String;[Ljava/lang/Object;，如果不满足则直接抛出异常

decode完成之后将调用HeaderExchangeHandler.java#received方法处理请求，若为泛型引用，则将调用GenericFilter#invoke方法

判断是否满足泛型引用条件，通过getArguments()方法获取参数，并取第一个参数为方法名，第二个参数为方法名的类型，第三个参数为args。通过反射寻找服务端提供的方法，如果没有找到则抛出异常。

接下来将通过获取请求中的generic参数来选择通过raw.return/nativejava/bean反序列化参数成pojo对象，这个CVE漏洞的入口就在这里了

我们依次分析一下触发点

1、设置generic为raw.return或者true，将调用PojoUtils#realize方法

PojoUtils.realize(args, params, method.getGenericParameterTypes());
// PojoUtils#realize    public static Object[] realize(Object[] objs, Class<?>[] types, Type[] gtypes)    {        ...        Object[] dests = new Object[objs.length];        for (int i = 0; i < objs.length; i++) {            dests[i] = realize(objs[i], types[i], gtypes[i]);        }

调用PojoUtils#realize

public static Object realize(Object pojo, Class<?> type, Type genericType) {        return realize0(pojo, type, genericType, new IdentityHashMap<Object, Object>());

调用PojoUtils#realize0，若pojo为Map实例，则从pojo（也就是一开始的第三个参数）获取key为“class”的值，并通过反射得到class所对应的类type，再判断对象的类型进行下一步处理

如果type不是Map的子类、不为Object.class且不是接口，则进入else，在else中，对type通过反射进行了实例化，得到对象dest

再对pojo进行遍历，以键名为name，值为value，调用getSetterMethod(dest.getClass(), name, value.getClass());获取set方法

最后利用反射执行method.invoke(dest, value);，就可以使用org.apache.xbean.propertyeditor.JndiConverter的setAsText发起JNDI注入了

private static Object realize0(Object pojo, Class<?> type, Type genericType, final Map<Object, Object> history) {      ...        if (pojo instanceof Map<?, ?> && type != null) {            Object className = ((Map<Object, Object>) pojo).get("class");            if (className instanceof String) {                try {                    type = ClassUtils.forName((String) className);                } catch (ClassNotFoundException e) {                    // ignore                }            }            ...            Map<Object, Object> map;            if (!type.isInterface() && !type.isAssignableFrom(pojo.getClass())) {                try {                    ...                } catch (Exception e) {                    map = (Map<Object, Object>) pojo;                }            }        if (Map.class.isAssignableFrom(type) || type == Object.class) {...}        else if (type.isInterface()) {...}        else {            Object dest = newInstance(type);                history.put(pojo, dest);                for (Map.Entry<Object, Object> entry : map.entrySet()) {                    Object key = entry.getKey();                    if (key instanceof String) {                        String name = (String) key;                        Object value = entry.getValue();                        if (value != null) {                            // 获取对应的set方法                            Method method = getSetterMethod(dest.getClass(), name, value.getClass());                            Field field = getField(dest.getClass(), name);                            if (method != null) {                                if (!method.isAccessible()) {                                    method.setAccessible(true);                                }                                Type ptype = method.getGenericParameterTypes()[0];                                value = realize0(value, method.getParameterTypes()[0], ptype, history);                                try {                                    // 反射执行方法                                    method.invoke(dest, value);                                } catch (Exception e) {...}                                else if (field != null) {...}                                        }

调用栈如下：

setAsText:59, AbstractConverter (org.apache.xbean.propertyeditor)invoke0:-1, NativeMethodAccessorImpl (sun.reflect)invoke:62, NativeMethodAccessorImpl (sun.reflect)invoke:43, DelegatingMethodAccessorImpl (sun.reflect)invoke:497, Method (java.lang.reflect)realize0:483, PojoUtils (org.apache.dubbo.common.utils)realize:211, PojoUtils (org.apache.dubbo.common.utils)realize:99, PojoUtils (org.apache.dubbo.common.utils)invoke:91, GenericFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)invoke:38, ClassLoaderFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)invoke:41, EchoFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)reply:145, DubboProtocol$1 (org.apache.dubbo.rpc.protocol.dubbo)received:152, DubboProtocol$1 (org.apache.dubbo.rpc.protocol.dubbo)received:177, HeaderExchangeHandler (org.apache.dubbo.remoting.exchange.support.header)received:51, DecodeHandler (org.apache.dubbo.remoting.transport)run:57, ChannelEventRunnable (org.apache.dubbo.remoting.transport.dispatcher)runWorker:1142, ThreadPoolExecutor (java.util.concurrent)run:617, ThreadPoolExecutor$Worker (java.util.concurrent)run:745, Thread (java.lang)

2、设置generic为bean，将遍历args，如果args[i]为JavaBeanDescriptor的实例，则调用JavaBeanSerializeUtil#deserialize进行处理

JavaBeanSerializeUtil.deserialize((JavaBeanDescriptor) args[i]);
// JavaBeanSerializeUtil#deserialize    public static Object deserialize(JavaBeanDescriptor beanDescriptor) {        return deserialize(                beanDescriptor,                Thread.currentThread().getContextClassLoader());    }

调用

JavaBeanSerializeUtil#instantiateForDeserialize以获得对象，name2Class负责把 Class.forName 的返回值转换为 Class，而instantiate则实例化对象，最终返回一个JavaBeanDescriptor描述的对象

private static Object instantiateForDeserialize(JavaBeanDescriptor beanDescriptor, ClassLoader loader,IdentityHashMap<JavaBeanDescriptor, Object> cache) {        ...        Object result;        if (beanDescriptor.isArrayType()) {...}        else {            try {                Class<?> cl = name2Class(loader, beanDescriptor.getClassName());                result = instantiate(cl);                cache.put(beanDescriptor, result);            } catch (Exception e) {                throw new RuntimeException(e.getMessage(), e);            }        }        return result;    }

接着调用JavaBeanSerializeUtil#deserializeInternal进行反序列化，如果beanDescriptor.isBeanType()（只需要实例化JavaBeanDescriptor时指定即可），则将遍历beanDescriptor，获取property及value，调用getSetterMethod获取对应的set方法

最后利用反射执行method.invoke(dest, value);，就可以使用org.apache.xbean.propertyeditor.JndiConverter的setAsText发起JNDI注入了

private static void deserializeInternal(Object result, JavaBeanDescriptor beanDescriptor, ClassLoader loader,IdentityHashMap<JavaBeanDescriptor, Object> cache) {        if (beanDescriptor.isEnumType() || beanDescriptor.isClassType() || beanDescriptor.isPrimitiveType()) {            return;        }        if(beanDescriptor.isArrayType()){...}        ...        else if (beanDescriptor.isBeanType()) {            for (Map.Entry<Object, Object> entry : beanDescriptor) {                String property = entry.getKey().toString();                Object value = entry.getValue();                if (value == null) {                    continue;                }                if (value instanceof JavaBeanDescriptor) {...}                // 获取对应的set方法                Method method = getSetterMethod(result.getClass(), property, value.getClass());                boolean setByMethod = false;                try {                    if (method != null) {                        // 反射执行方法                        method.invoke(result, value);                        setByMethod = true;                    }                }catch (Exception e) {                    ...                }        }

调用栈如下：

setAsText:59, AbstractConverter (org.apache.xbean.propertyeditor)invoke0:-1, NativeMethodAccessorImpl (sun.reflect)invoke:62, NativeMethodAccessorImpl (sun.reflect)invoke:43, DelegatingMethodAccessorImpl (sun.reflect)invoke:497, Method (java.lang.reflect)deserializeInternal:282, JavaBeanSerializeUtil (org.apache.dubbo.common.beanutil)deserialize:215, JavaBeanSerializeUtil (org.apache.dubbo.common.beanutil)deserialize:204, JavaBeanSerializeUtil (org.apache.dubbo.common.beanutil)invoke:115, GenericFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)invoke:38, ClassLoaderFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)invoke:41, EchoFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)reply:145, DubboProtocol$1 (org.apache.dubbo.rpc.protocol.dubbo)received:152, DubboProtocol$1 (org.apache.dubbo.rpc.protocol.dubbo)received:177, HeaderExchangeHandler (org.apache.dubbo.remoting.exchange.support.header)received:51, DecodeHandler (org.apache.dubbo.remoting.transport)run:57, ChannelEventRunnable (org.apache.dubbo.remoting.transport.dispatcher)runWorker:1142, ThreadPoolExecutor (java.util.concurrent)run:617, ThreadPoolExecutor$Worker (java.util.concurrent)run:745, Thread (java.lang)

3、设置generic为nativejava，将遍历args，如果args[i]的类型为byte，以args[]为参实例化一个UnsafeByteArrayInputStream，再通过反射获得NativeJavaSerialization，再调用NativeJavaSerialization#readObject方法

if (byte[].class == args[i].getClass()) {    try (UnsafeByteArrayInputStream is = new UnsafeByteArrayInputStream((byte[]) args[i])) {        args[i] = ExtensionLoader.getExtensionLoader(Serialization.class).getExtension(GENERIC_SERIALIZATION_NATIVE_JAVA).deserialize(null, is).readObject();          } catch (Exception e) {     throw new RpcException("Deserialize argument [" + (i + 1) + "] failed.", e);    }}else{...}

NativeJavaSerialization#readObject调用inputStream的readObject()方法，相当于调用了UnsafeByteArrayInputStream的readObject()方法

由于UnsafeByteArrayInputStream没有readObject()故调用ObjectInputStream#readObject()方法进行反序列化，我们可以通过以此为入口触发CC4的gadget

 public Object readObject() throws IOException, ClassNotFoundException {        return inputStream.readObject();    }

调用栈如下：

readObject:371, ObjectInputStream (java.io)readObject:50, NativeJavaObjectInput (org.apache.dubbo.common.serialize.nativejava)invoke:98, GenericFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)invoke:38, ClassLoaderFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)invoke:41, EchoFilter (org.apache.dubbo.rpc.filter)invoke:83, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)reply:145, DubboProtocol$1 (org.apache.dubbo.rpc.protocol.dubbo)received:152, DubboProtocol$1 (org.apache.dubbo.rpc.protocol.dubbo)received:177, HeaderExchangeHandler (org.apache.dubbo.remoting.exchange.support.header)received:51, DecodeHandler (org.apache.dubbo.remoting.transport)run:57, ChannelEventRunnable (org.apache.dubbo.remoting.transport.dispatcher)runWorker:1142, ThreadPoolExecutor (java.util.concurrent)run:617, ThreadPoolExecutor$Worker (java.util.concurrent)run:745, Thread (java.lang)