What Information in a Java Error Stack Trace Should Not Be Displayed to Users?

What specific details in a Java error stack trace should be kept hidden from end-users for security reasons?

When an error occurs in a Java application, a stack trace is generated that includes detailed debugging information. However, it is crucial to avoid showing users certain sensitive details in this error output to maintain security and improve user experience. Below, we discuss the types of information typically concealed from users in a Java error stack trace.

try {
    // Some code that might throw an exception
} catch (Exception e) {
    // Log the exception details for the developers
    Logger.error(e);
    // Display a generic error message to the user
    System.out.println("An error occurred. Please try again later.");
}

Causes

• Internal file paths that can expose directory structure.
• Detailed exception classes that might offer clues about the application's internals.
• Sensitive data parameters that can include passwords or personally identifiable information (PII).
• Verbose application-specific error messages that reveal implementation details.

Solutions

• Use a generic error message to inform users of a problem without exposing details.
• Log the full stack trace to a server log for developers to review, but show only a user-friendly message on the UI.
• Implement error handling middleware to capture exceptions and sanitize outputs before sending to the user.
• Provide an option for users to report issues without showing technical details. For example, 'An unexpected error occurred. We are investigating it.'

Mistake: Displaying full stack traces directly to the user.

Solution: Always sanitize stack traces by providing generic error messages instead.

Mistake: Including internal application paths in user messages.

Solution: Use a tool or library to sanitize error messages before displaying them.

Mistake: Failing to log the details of the stack trace for developers.

Solution: Ensure proper logging mechanisms are in place to capture errors without exposing them to users.