FIO33-J. Do not allow serialization and deserialization to bypass the Security Manager

The serialization and deserialization features can be exploited to bypass security manager checks. A serializable class may employ security manager checks in its constructors for various reasons. For example, the checks prevent an attacker from modifying the internal state of the class.

Noncompliant Code Example

In this noncompliant example, security manager checks are used within the constructor but are not replicated throughout, specifically, within the readObject and writeObject methods that are used in the serialization-deserialization process. This allows an attacker to maliciously create instances of the class that bypass security manager checks when deserialization is performed.

import java.io.Serializable;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public final class CreditCard implements Serializable {

  //private internal state
  private String credit_card;
  private static final String DEFAULT = "DEFAULT";

  public CreditCard() {
    //initialize credit_card to default value
    credit_card = DEFAULT;
  }

  //allows callers to modify (private) internal state
  public void changeCC(String newCC) {
    if (credit_card.equals(newCC)) {
      // no change
      return;
    } else {  
      validateInput(newCC);
      credit_card = newCC;
    }
  }

  // readObject correctly enforces checks during deserialization
  private void readObject(ObjectInputStream in) {
    in.defaultReadObject();
    // if the deserialized name does not match the default value normally
    // created at construction time, duplicate the checks
    if (!DEFAULT.equals(credit_card)) {
      validateInput(credit_card);
    }
  }

  // allows callers to retrieve internal state
  public String getValue() {
    return somePublicValue;
  }

  // writeObject correctly enforces checks during serialization
  private void writeObject(ObjectOutputStream out) {
    out.writeObject(credit_card);
  }
}

Compliant Solution

The compliant solution correctly implements security manager checks in all constructors, methods that can modify internal state and methods that retrieve internal state. As a result, an attacker cannot create an instance of the object with modified state (using deserialization) and cannot simply read the serialized byte stream to uncover sensitive data (using serialization).

public final class SecureCreditCard implements java.io.Serializable {

  //private internal state
  private String credit_card;
  private static final String DEFAULT = "DEFAULT";

  public SecureCreditCard() {
    //initialize credit_card to default value
    credit_card = DEFAULT;
  }

  //allows callers to modify (private) internal state
  public void changeCC(String newCC) {
    if (credit_card.equals(newCC)) {
      // no change
      return;
    } else {
      // check permissions to modify credit_card
      performSecurityManagerCheck();
      validateInput(newCC);
      credit_card = newCC;
    }
  }

  // readObject correctly enforces checks during deserialization
  private  readObject(java.io.ObjectInputStream in) {
    defaultReadObject();
    // if the deserialized name does not match the default value normally
    // created at construction time, duplicate the checks
    if (!DEFAULT.equals(credit_card)) {
      performSecurityManagerCheck();
      validateInput(credit_card);
    }
  }

  // allows callers to retrieve internal state
  public String getValue() {
  // check permission to get value
    performSecurityManagerCheck();
    return somePublicValue;
  }

  // writeObject correctly enforces checks during serialization
  private void writeObject(java.io.ObjectOutputStream out) {
    // duplicate check from getValue()
    performSecurityManagerCheck();
    out.writeObject(credit_card);
  }
}

Risk Assessment

Allowing serialization or deserialization to bypass the Security Manager may result in sensitive data being compromised or modified.

Rule	Severity	Likelihood	Remediation Cost	Priority	Level
FIO33-J	high	probable	high	P6	L2

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

[[SCG 07]] Guideline 5-3 Duplicate the SecurityManager checks enforced in a class during serialization and deserialization
[[Long 05]] Section 2.4, Serialization

FIO32-J. Do not serialize sensitive data 07. Input Output (FIO) FIO35-J. Exclude user input from format strings

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