J2EE Framework: Saving Unserializable Objects to Disk

Description

In heavy load conditions, most J2EE application frameworks flush objects to disk to manage memory requirements of incoming requests. For example, session scoped objects, and even application scoped objects, are written to disk when required. While these application frameworks do the real work of writing objects to disk, they do not enforce that those objects be serializable, thus leaving the web application vulnerable to crashes induced by serialization failure. An attacker may be able to mount a denial of service attack by sending enough requests to the server to force the web application to save objects to disk.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

In the following Java example, a Customer Entity JavaBean provides access to customer information in a database for a business application. The Customer Entity JavaBean is used as a session scoped object to return customer information to a Session EJB.

@Entity
public class Customer {


  private String id;
  private String firstName;
  private String lastName;
  private Address address;

  public Customer() {
  }

  public Customer(String id, String firstName, String lastName) {...}

  @Id
  public String getCustomerId() {...}

  public void setCustomerId(String id) {...}

  public String getFirstName() {...}

  public void setFirstName(String firstName) {...}

  public String getLastName() {...}

  public void setLastName(String lastName) {...}

  @OneToOne()
  public Address getAddress() {...}

  public void setAddress(Address address) {...}



}

However, the Customer Entity JavaBean is an unserialized object which can cause serialization failure and crash the application when the J2EE container attempts to write the object to the system. Session scoped objects must implement the Serializable interface to ensure that the objects serialize properly.

public class Customer implements Serializable {...}

See Also