SER32-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 untrusted code from modifying the internal state of the class.

Security manager checks must be replicated at all points where a class can be constructed. Because deserialization acts like a constructor, all the relevant methods must contain a security check.

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 serializing the object.

Noncompliant Code Example

In this noncompliant code example, security manager checks are used within the constructor but are not replicated within 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";

  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

This compliant solution implements the required security manager checks in all constructors and methods that can either modify or retrieve internal state. As a result, 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";

  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 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)) {
      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) {
    // 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 exposed or modified.

Rule	Severity	Likelihood	Remediation Cost	Priority	Level
SER32- 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

SER31-J. Validate deserialized objects 13. Serialization (SER) SER33-J. Do not serialize instances of inner classes

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