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Sensitive data may be compromised if its lifetime is not limited to the period of its usein memory can be vulnerable to compromise. An adversary who has control of the file system can execute code on the same system as an application may be able to access such data if the application:

• uses Uses objects to store sensitive data whose contents are not cleared or garbage-collected after use
• has Has memory pages that can be swapped out to disk as required by the operating system (for example, to perform memory management tasks and or to support hibernation)
• uses Holds sensitive data in a buffer to hold sensitive data (such as BufferedReader) that retains copies of the data in the OS cache or in memory
• bases Bases its control flow on Reflection reflection that allows circumventing any countermeasures to limit circumvent the limiting of the lifetime of sensitive variables
• reveals Reveals sensitive data in debugging messages, log files, environment variables, or through thread and core dumps

Sensitive data leaks become more likely if the memory containing the data is not cleared after using the data. To limit the risk of exposure, programs must minimize the lifetime of sensitive data.

Complete mitigation (that is, foolproof protection of data in memory) Currently, complete mitigation requires support from the underlying operating system and Java Virtual Machine. For instanceexample, if swapping out of sensitive data out to disk is an issue, a secure operating system that disables swapping and hibernation is indispensablerequired.

Noncompliant Code Example

This noncompliant code example reads login user name and password information from the console and stores the password as a a String object object. The credentials remain exposed until the garbage collector reclaims the memory associated with the this String objects.

class Password {
  public static void main (String args[]) throws IOException {
    Console c = System.console();
      if (c == null) {
        System.err.println("No console.");
        System.exit(1);
      }

      String loginusername = c.readLine("Enter your user name: ");
      String password = c.readLine("Enter your password: ");

      if (!verify(loginusername, password)) {
        throw new IOExceptionSecurityException("Invalid Credentials");     
      }

    // User is //authorized, continue...
  }

  // Dummy verify method, always returns true   
  private static final boolean verify(String loginusername, String password) {
    return true;
  }
}

Compliant Solution

This compliant solution uses the Console.readPassword() method to obtain the password from the console. This method allows the password to be returned as a sequence of characters as opposed to a String object. This allows the programmer to clear the password from the array immediately after use. The method also disables echoing of the password to the console.:

class Password {
  public static void main (String args[]) throws IOException {
    Console c = System.console();
    
    if (c == null) {
      System.err.println("No console.");
      System.exit(1);
    }

    String loginusername = c.readLine("Enter your user name: ");
    char [] password = c.readPassword("Enter your password: ");
  
  boolean isValidUser if= (!verify(login, password)username, password); 

    // Clear the password
    Arrays.fill(password,' ');

    if (!isValidUser) {
      throw new IOExceptionSecurityException("Invalid Credentials");     
    }
  
    // ClearUser theis password
    Arrays.fill(password, ' ');authorized, continue...
  }

  // Dummy verify method, always returns true   
  private static final boolean verify(String loginusername, char[] password) {
    return true;
  }
}

The Console.readPassword() method allows the password to be returned as a sequence of characters rather than as a String object. Because the password is never interned as a String, it will not survive garbage collection even if it matches another string. Consequently, the programmer can clear the password from the array immediately after use.

The Console.readPassword() method also disables echoing of the password to the console.

Noncompliant Code Example

This noncompliant code example uses a BufferedReader to wrap an InputStreamReader object so that sensitive data can be read from a file.:

void readData() throws IOException {
  BufferedReader br = new BufferedReader(new InputStreamReader(
  new FileInputStream("file")));
  // Read from the file
  String data = br.readLine();
}

The BufferedReader.readLine() method returns the sensitive data as a String object, which can persist long after the data is no longer needed. The BufferedReader.read(char[], int, int) method can read and populate a char array. However, it requires the programmer to manually clear the sensitive data in the array after use. Alternatively, even if the BufferedReader were to wrap a FileReader object, it would suffer from the same pitfalls.

Compliant Solution

This compliant solution uses a direct directly allocated NIO (new I/O) buffer to read sensitive data from the file. The data can be cleared immediately after use and is not cached or buffered at multiple locations. It exists only in the system memory.

private void readIntoDirectBufferreadData() throws IOException { {
  int bufferSize = 16 * 1024;
  byte zeroes = new byte[bufferSize];
  ByteBuffer buffer = ByteBuffer.allocateDirect(16 * 1024bufferSize);
  try (FileChannel rdr = (new FileInputStream("file")).getChannel();) {
   	while (rdr.read(buffer) > 0) {

      // Do something with the buffer

	  buffer.clear();
      buffer.put(zeroes); // overwrite buffer with zeroes
	  buffer.clear();
	}
  }
 catch rdr.close();Throwable e) {
    // Handle error
  }
} 

Note that manual clearing of the buffer data is mandatory because direct buffers are not subject to garbage collectioncollected.

Exceptions

EX1: This guideline may be violated iff:
1. It can be proved that the code is free from other errors that can expose the sensitive data.
2. An attacker does not have physical access to the target machine.

Risk Assessment

Applicability

Failure to limit the lifetime of sensitive data can lead to information leaks.

Automated Detection

TODO

Related Vulnerabilities

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

References

\[[API 06|AA. Java References#API 06]\] Class {{java.nio.ByteBuffer}}
\[[Tutorials 08|AA. Java References#Tutorials 08]\] [I/O from the Command Line|http://java.sun.com/docs/books/tutorial/essential/io/cl.html]
\[[Sun 06|AA. Java References#Sun 06]\] [Reading ASCII Passwords From an InputStream Example|http://java.sun.com/javase/6/docs/technotes/guides/security/crypto/CryptoSpec.html#ReadPassword] (JCA Reference Guide)
\[[MITRE 09|AA. Java References#MITRE 09]\] [CWE ID 524|http://cwe.mitre.org/data/definitions/524.html] "Information Leak Through Caching", [CWE ID 528|http://cwe.mitre.org/data/definitions/528.html] "Information Leak Through Core Dump Files", [CWE ID 215|http://cwe.mitre.org/data/definitions/215.html] "Information Leak Through Debug Information", [CWE ID 534|http://cwe.mitre.org/data/definitions/534.html] "Information Leak Through Debug Log Files", [CWE ID 526|http://cwe.mitre.org/data/definitions/526.html] "Information Leak Through Environmental Variables" and [CWE ID 226|http://cwe.mitre.org/data/definitions/226.html] "Sensitive Information Uncleared Before Release"

Bibliography

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Image Added Image Added Image AddedMSC09-J. Carefully design interfaces before releasing them      49. Miscellaneous (MSC)      MSC11-J. Do not assume infinite heap space