FIO08-J. Do not log sensitive information outside a trust boundary

Logging is essential for gathering debugging information, for carrying out incident response or forensics activities and for maintaining incriminating evidence. Nevertheless, logging sensitive data raises many concerns, including the privacy of the stakeholders, limitations imposed by the law on the collection of personal information, and the potential for data exposure through insiders. Sensitive information includes, but is not limited to, IP addresses, user names and passwords, email addresses, credit card numbers and any personally identifiable information such as social security numbers. Many countries prohibit or restrict collection of personal data; others permit retention of personal data only when held in an anonymized form. Consequently, ensure that logs contain only non-sensitive data.

Violations of this guideline are common. For example, prior to version 0.8.1, LineControl Java client logged sensitive information including the local user's password [[CVE 2008]].

The java.util.logging class provides the basic logging framework in JDK v1.4 and above; the examples below use the logging framework. The basic principles apply regardless of the particular logging framework chosen.

A program may support multiple levels of sensitivity. Some information, such as access times can be safely logged. Some infomration can be logged, but the log file must be restricted from everyone but particular administrators. Other information, such as credit card numbers can only be logged in encrypted form. Other information, such as passwords, should not be logged at all.

For these code samples, we will assume that the log in question lies outside the trust boundary of the information being sent to it. Also, normal log messages should include additional parameters such as date, time, source event, etc.. We omit them in these examples for the sake of brevity.

Noncompliant Code Example

In this noncompliant code example, a server logs the IP address of the remote client in the event of a security exception. Such data can be misused in various ways, such as building a profile of a user's browsing habits. Such logging may violate legal restrictions in many countries.

If the log cannot be trusted to hold the IP address, it should not hold any info about a SecurityException. When an exception contains sensitive information, the custom MyExceptionReporter class should extract or cleanse it, before returning control to the next statement in the catch block. (See guideline ERR00-J. Do not suppress or ignore checked exceptions.)

public void logRemoteIPAddress(String name) {
  Logger logger = Logger.getLogger("com.organization.Log");
  InetAddress machine = null;
  try {
    machine = InetAddress.getByName(name);
  } catch (UnknownHostException e) { 
    Exception e = MyExceptionReporter.handle(e);
  } catch (SecurityException e) {
    Exception e = MyExceptionReporter.handle(e);
    logger.severe(name + "," + machine.getHostAddress() + "," + e.toString());
  }
} 

Compliant Solution

This compliant solution simply does not log the security exception.

   // ...
  catch (SecurityException e) {
    Exception e = MyExceptionReporter.handle(e);
  }

Noncompliant Code Example

Some information that is logged should be elided from console display for security reasons (a possible example might be passenger age). The java.util.logging.Logger class supports different logging levels that can be used for classifying such information. These are FINEST, FINER, FINE, CONFIG, INFO, WARNING and SEVERE. All levels after and including INFO, log the message to the console in addition to an external source.

logger.info("Age: " + passengerAge);

By default, log messages with level INFO are displayed to the console.

Compliant Solution

This noncompliant code example logs at a level below INFO — FINEST, in this case — to prevent the passenger age from being displayed on the console. It also makes sure that such messages do not appear on the console. Thus the age is not actually logged.

Handler handlers[] = logger.getHandlers();
for (int i = 0; i < handlers.length; i++) {
  handlers[i].setLevel(Level.INFO);
}
// ...
logger.finest("Age: " + passengerAge);

Risk Assessment

Logging sensitive information can violate system security policies and can violate user privacy when the logging level is incorrect or when the log files are insecure.

Related Vulnerabilities

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

Bibliography

[[API 2006]]] Class java.util.logging.Logger
[[Chess 2007]]] 11.1 Privacy and Regulation: Handling Private Information
[[CVE 2008]]] CVE-2005-2990
[[MITRE 2009]] CWE ID 532 "Information Leak Through Log Files", CWE ID 533 "Information Leak Through Server Log Files", CWE ID 359 "Privacy Violation", CWE ID 542 "Information Leak Through Cleanup Log Files"
[[Sun 2006]]] Java Logging Overview

FIO07-J. Do not create temporary files in shared directories      12. Input Output (FIO)      FIO10-J. Do not let Runtime.exec() fail or block indefinitely