Secure Logging and Preventing Sensitive Data Leaks

Learn secure logging in Java applications, including redaction, structured logs, audit events, sensitive data prevention, token masking, and production logging practices.

What You Will Learn

What should never be logged.
How to redact sensitive values.
Difference between application logs and audit logs.
How structured logging helps.
Production logging safeguards.

Introduction

Logs are useful for debugging and operations, but they can become a data leak.

Sensitive data often leaks through:

Request bodies.
Headers.
Exceptions.
Debug logs.
Third-party client logs.

Never Log

Passwords.
Access tokens.
Refresh tokens.
API keys.
Full SSNs.
Full card numbers.
Private keys.
Session cookies.

Secure Logging Flow

flowchart LR
    A["Request"] --> B["Redaction filter"]
    B --> C["Structured log event"]
    C --> D["Central log platform"]
    D --> E["Access-controlled search"]

Redaction Example

String redactAuthorization(String value) {
    if (value == null || value.isBlank()) {
        return value;
    }
    return "[REDACTED]";
}

Audit Logs

Audit logs record security-relevant events.

Examples:

Login success or failure.
Password reset.
Role change.
Sensitive data access.
MFA disabled.
Admin action.

Best Practices

Use structured logs.
Redact secrets before logging.
Limit log access.
Set retention policies.
Avoid logging full request bodies.
Add correlation IDs.
Monitor suspicious events.

Summary

Secure logging gives visibility without exposing users or systems. Redact sensitive values, separate audit events, and control access to logs.