SER05-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 install security manager checks in its constructors for various reasons including, for example, preventing untrusted code from modifying the internal state of the class. Such security manager checks must be replicated at all points where a class instance can be constructed. Because deserialization acts like a constructor, all the relevant methods must contain all relevant security checks.

If the class enables a caller to retrieve sensitive internal state contingent upon security checks, the same checks must be replicated during deserialization. This ensures that an attacker cannot glean sensitive information by deserializing the object.

Noncompliant Code Example

In this noncompliant code example, security manager checks are used within the constructor but are omitted from the writeObject() and readObject() methods that are used in the serialization-deserialization process. This allows untrusted code to maliciously create instances of the class.

public final class CreditCard implements Serializable {
  // Private internal state
  private String credit_card;
  private static final String DEFAULT = "DEFAULT";

  void performSecurityManagerCheck() throws AccessDeniedException {
    // ...
  }

  void validateInput(String newCC) throws InvalidInputException {
    // ...
  }

  public CreditCard() throws AccessDeniedException {
    performSecurityManagerCheck();

    // Initialize credit_card to default value
    credit_card = DEFAULT;
  }

  // Allows callers to modify (private) internal state
  public void changeCC(String newCC) throws InvalidInputException {
    if (credit_card.equals(newCC)) {
      // No change
      return;
    } else {  
      performSecurityManagerCheck();
      validateInput(newCC);
      credit_card = newCC;
    }
  }

  // readObject() correctly enforces checks during deserialization
  private void readObject(ObjectInputStream in)  throws IOException, InvalidInputException {
    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
  String getValue() {
    return credit_card;
  }

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

Compliant Solution

This compliant solution implements the required security manager checks in all constructors and methods that can either modify or retrieve internal state. Consequently, an attacker cannot create a modified instance of the object (using deserialization) or read the serialized byte stream to uncover sensitive serialized data.

public final class SecureCreditCard implements Serializable {
  // Private internal state
  private String credit_card;
  private static final String DEFAULT = "DEFAULT";

  void performSecurityManagerCheck() throws AccessDeniedException {
    // ...
  }

  void validateInput(String newCC) throws InvalidInputException {
    // ...
  }

  public SecureCreditCard() throws AccessDeniedException {
    performSecurityManagerCheck();

    // Initialize credit_card to default value
    credit_card = DEFAULT;
  }

  //allows callers to modify (private) internal state
  public void changeCC(String newCC) throws AccessDeniedException, InvalidInputException {
    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 void readObject(ObjectInputStream in)  throws IOException {
    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(ObjectOutputStream out)  throws IOException {
    // Duplicate check from getValue()
    performSecurityManagerCheck();
    out.writeObject(credit_card);
  }
}

Refer to guideline SEC08-J. Protect sensitive operations with security manager checks to learn about implementing the performSecurityManagerCheck() method. As with guideline SER04-J. Validate deserialized objects, it is important to protect against the finalizer attack.

Risk Assessment

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

Guideline	Severity	Likelihood	Remediation Cost	Priority	Level
SER05-J	high	probable	high	P6	L2

Related Vulnerabilities

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

Bibliography

[[Long 2005]] Section 2.4, Serialization
[[SCG 2007]] Guideline 5-3 Duplicate the SecurityManager checks enforced in a class during serialization and deserialization

SER04-J. Validate deserialized objects 16. Serialization (SER) SER06-J. Do not serialize instances of inner classes

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Noncompliant Code Example

Compliant Solution

Risk Assessment

Related Vulnerabilities

Bibliography