IDS03-J. Do not log unsanitized user input

A log injection vulnerability arises when a log entry contains unsanitized user input. A malicious user can insert fake log data and consequently deceive system administrators as to the system's behavior [OWASP 2008]. For example, an attacker might split a legitimate log entry into two log entries by entering a carriage return and line feed (CRLF) sequence to mislead an auditor. Log injection attacks can be prevented by sanitizing and validating any untrusted input sent to a log.

Logging unsanitized user input can also result in leaking sensitive data across a trust boundary. For example, an attacker might inject a script into a log file such that when the file is viewed using a web browser, the browser could provide the attacker with a copy of the administrator's cookie so that the attacker might gain access as the administrator.

Noncompliant Code Example

This noncompliant code example logs untrusted data from an unauthenticated user without data sanitization.

if (loginSuccessful) {
  logger.severe("User login succeeded for: " + username);
} else {
  logger.severe("User login failed for: " + username);
}

Without sanitization, a log injection attack is possible. A standard log message when username is guest might look like this:

May 15, 2011 2:19:10 PM java.util.logging.LogManager$RootLogger log
SEVERE: User login failed for: guest 

If the username that is used in a log message is not guest but rather a multiline string like this:

guest 
May 15, 2011 2:25:52 PM java.util.logging.LogManager$RootLogger log
SEVERE: User login succeeded for: administrator

the log would contain the following misleading data:

May 15, 2011 2:19:10 PM java.util.logging.LogManager$RootLogger log
SEVERE: User login failed for: guest 
May 15, 2011 2:25:52 PM java.util.logging.LogManager log
SEVERE: User login succeeded for: administrator

Compliant Solution

This compliant solution validates the username input before logging it, preventing injection attacks.

if (!Pattern.matches("[A-Za-z0-9_]+", username)) {
  // Unsanitized username
  logger.severe("User login failed for unauthorized user");
} else if (loginSuccessful) {
  logger.severe("User login succeeded for: " + username);
} else {
  logger.severe("User login failed for: " + username);
}

Risk Assessment

Allowing unvalidated user input to be logged can result in forging of log entries, leaking secure information, or storing sensitive data in a manner that violates a local law or regulation.

Automated Detection

Related Guidelines

Bibliography

[API 2006]	Java Platform, Standard Edition 6 API Specification
[OWASP 2008]
[Seacord 2015]	IDS03-J. Do not log unsanitized user input LiveLesson