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, a user might split a legitimate log entry into two log entries by entering a carriage return and line feed (CRLF) sequence, either of which might be misleading. 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 the log file such that, if viewed using a web browser, could provide the attacker with a copy of the operator/administrator's cookie so that he might gain access as that user. See IDS00-J. Prevent SQL Injection for more details on input sanitization.

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 was 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 just 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