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Neste POST, será explicado um exemplo usando `java.io.Serializable`.
# Serializable
A interface Java `Serializable` (`java.io.Serializable` é uma interface de marcador que suas classes devem implementar se forem **serializadas** e **desserializadas**. A serialização de objetos Java (escrita) é feita com o [ObjectOutputStream](http://tutorials.jenkov.com/java-io/objectoutputstream.html) e a desserialização (leitura) é feita com o [ObjectInputStream](http://tutorials.jenkov.com/java-io/objectinputstream.html).
Vamos ver um exemplo com uma **classe Person** que é **serializável**. Esta classe **sobrescreve a função readObject**, então quando **qualquer objeto** desta **classe** é **desserializado**, esta **função** será **executada**.\
No exemplo, a **função readObject** da classe Person chama a função `eat()` de seu animal de estimação e a função `eat()` de um Dog (por algum motivo) chama um **calc.exe**. **Vamos ver como serializar e desserializar um objeto Person para executar esta calculadora:**
**O seguinte exemplo é de [https://medium.com/@knownsec404team/java-deserialization-tool-gadgetinspector-first-glimpse-74e99e493649](https://medium.com/@knownsec404team/java-deserialization-tool-gadgetinspector-first-glimpse-74e99e493649)**
```java
import java.io.Serializable;
import java.io.*;
public class TestDeserialization {
interface Animal {
public void eat();
}
//Class must implements Serializable to be serializable
public static class Cat implements Animal,Serializable {
@Override
public void eat() {
System.out.println("cat eat fish");
}
}
//Class must implements Serializable to be serializable
public static class Dog implements Animal,Serializable {
@Override
public void eat() {
try {
Runtime.getRuntime().exec("calc");
} catch (IOException e) {
e.printStackTrace();
}
System.out.println("dog eat bone");
}
}
//Class must implements Serializable to be serializable
public static class Person implements Serializable {
private Animal pet;
public Person(Animal pet){
this.pet = pet;
}
//readObject implementation, will call the readObject from ObjectInputStream and then call pet.eat()
private void readObject(java.io.ObjectInputStream stream)
throws IOException, ClassNotFoundException {
pet = (Animal) stream.readObject();
pet.eat();
}
}
public static void GeneratePayload(Object instance, String file)
throws Exception {
//Serialize the constructed payload and write it to the file
File f = new File(file);
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(f));
out.writeObject(instance);
out.flush();
out.close();
}
public static void payloadTest(String file) throws Exception {
//Read the written payload and deserialize it
ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
Object obj = in.readObject();
System.out.println(obj);
in.close();
}
public static void main(String[] args) throws Exception {
// Example to call Person with a Dog
Animal animal = new Dog();
Person person = new Person(animal);
GeneratePayload(person,"test.ser");
payloadTest("test.ser");
// Example to call Person with a Cat
//Animal animal = new Cat();
//Person person = new Person(animal);
//GeneratePayload(person,"test.ser");
//payloadTest("test.ser");
}
}
```
## Conclusão
Como você pode ver neste exemplo muito básico, a "vulnerabilidade" aqui aparece porque a função **readObject** está **chamando outras funções vulneráveis**.
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