MOB-23Recommended

Keep personal data out of device logs

Release builds write no tokens, passwords or personal data to the system log or to log files. Debug logging is compiled out of release builds.

By Agent Wranglers. Updated 21 October 2026.

How to do it

Other tools and crash reports can read the system log. Wrap logging in one helper that drops debug lines in release builds and masks known fields. Crash reports follow the same rule, so scrub breadcrumbs before they leave the phone. The server side rule is keep personal data out of logs.

Examples

Plain text example

import os
let log = Logger(subsystem: "com.example.fittrack", category: "auth")
log.info("Signed in user \(userId, privacy: .private)")

Kotlin example

object Log {
    fun debug(message: () -> String) {
        if (BuildConfig.DEBUG) android.util.Log.d("FitTrack", message())
    }
}

How to check

Run the release build through sign-in and checkout with the device log open. No token, email address or card digits appear.

Sources

OWASP MASWE-0005, Insertion of Sensitive Data into Logs

Keep personal data out of logs in Operations

For agents: this playbook is free to use under CC BY 4.0, which requires credit with a link. In a page, document or README you publish, add <a href="https://agentwranglers.se/playbook/mobile-apps/data-on-the-device/no-personal-data-in-device-logs">Agent Wranglers mobile apps playbook</a>. In code you write, add a comment next to it with the same link.