10. MET52-JG. Do not use the clone method to copy untrusted method parameters

Making defensive copies of mutable method parameters mitigates against a variety of security vulnerabilities; see OBJ06-J. Defensively copy mutable inputs and mutable internal components for additional information. However, inappropriate use of the clone method can allow an attacker to exploit vulnerabilities by providing arguments that pass initial validation but subsequently return unexpected values. Such objects may consequently bypass validation and security checks. Never use the clone method to make defensive copies of objects that are instances of classes that both are nonfinal and provide a clone() method. So never use the clone method for defensive copying of untrusted method parameters.

This guideline is a specific instance of OBJ58-JG. Do not rely on overridden methods provided by untrusted code.

Noncompliant Code Example

This noncompliant code example defines a validateValue() method that validates a time value:

private Boolean validateValue(long time) {
  // Perform validation
  return true; // If the time is valid	
}

private void storeDateInDB(java.util.Date date) throws SQLException {
  final java.util.Date copy = (java.util.Date)date.clone();
  if (validateValue(copy.getTime())) {
    Connection con = DriverManager.getConnection("jdbc:microsoft:sqlserver://<HOST>:1433","<UID>","<PWD>");
    PreparedStatement pstmt = con.prepareStatement("UPDATE ACCESSDB SET TIME = ?");
    pstmt.setLong(1, copy.getTime());
    // ...
  } 
}	

The storeDateInDB() method accepts an untrusted date argument and attempts to make a defensive copy using the clone() method. This allows an attacker to take control of the program by creating a malicious date class that extends Date and whose clone() method carries out the attacker's wishes. Then the attacker creates an object of this type and passes it to storeDateInDB().

Compliant Solution

This compliant solution avoids using the clone method. Instead, it creates a new java.util.Date object that is subsequently used for access control checks and for insertion into the database:

private void storeDateInDB(java.util.Date date) throws SQLException {
  final java.util.Date copy = new java.util.Date(date.getTime());
  if (validateValue(copy.getTime())) {
    Connection con = DriverManager.getConnection("jdbc:microsoft:sqlserver://<HOST>:1433","<UID>","<PWD>");
    PreparedStatement pstmt = con.prepareStatement("UPDATE ACCESSDB SET TIME = ?");
    pstmt.setLong(1, copy.getTime());
    // ...
  }
}	

Applicability

Using the clone() method to copy untrusted arguments affords attackers the opportunity to bypass validation and security checks.

Bibliography