How does App Passwords work?

How App Passwords fit into legacy authentication

app passwords are a compatibility bridge, not a modern access model. They exist because some older mail, calendar, scanning, or desktop applications can only handle a single static password and cannot complete MFA challenges. That makes them useful for continuity, but it also means they inherit the security profile of a reusable secret rather than a phishing-resistant sign-in flow.

Once issued, an App Password usually behaves like a standalone secret that can be stored in the app, cached on a device, or entered into a setup screen and then reused until revoked. In practice, that means the control boundary shifts from interactive sign-in to secret handling, which is why these passwords should be limited to the smallest possible user set and removed when the app can move to modern authentication.

Why they are treated as high-value secrets

Because an App Password bypasses MFA, anyone who obtains it can often authenticate directly as that user in the legacy app path. The security question is not only whether the password is strong, but whether the app, device, and support process around it can keep the secret from being copied, exported, logged, or reused elsewhere.

The practical risk is broader than initial login. If the password is embedded in an unattended client, stored in plain text, or shared across multiple systems, it can become a durable foothold that survives beyond the original setup event. That is why teams should treat each App Password as a narrowly scoped credential with a defined owner and a clear retirement plan.

When to use, and when to remove, an App Password

Use an App Password only when a legacy application cannot complete modern authentication and there is no reasonable short-term replacement. Even then, keep the exception narrow: one app, one user, one purpose, and one reviewable business need. Broad or indefinite use usually indicates the migration has stalled and the exception has become the default.

The decision to retire it should be tied to the app's authentication capability, not to user convenience. If the application can move to modern sign-in, the App Password should be disabled promptly rather than left in place as a fallback. A good migration pattern is to replace the secret at the same time the app is reconfigured, so there is no overlap between the old and new access method.

Risk and Threat Considerations

App Passwords create a direct bypass around MFA, so compromise of the secret can turn a protected account into a reusable login path for legacy software. That matters most where the app has access to email, files, administrative consoles, or other high-impact services, because the stolen secret can be used without triggering the extra step that MFA would normally impose.

Failure mechanism: The secret is copied from a device, backup, config file, or user process and then reused outside the intended legacy app path. Because the password is static and often long-lived, the attacker can keep using it until the organization notices and revokes it.

Impact: The attacker may gain direct account access through the legacy channel, pivot into mailbox or data access, and bypass the protection the organization assumed MFA was providing. If the app is privileged or broadly trusted, the blast radius can extend well beyond a single user session.

Practitioner Guidance

What to verify: Confirm which applications still require App Passwords, who owns each exception, and whether the app can be moved to modern authentication now or in the next change cycle. If the answer is unclear, the exception is probably wider than it should be.

What to prioritise: Start with any App Password tied to privileged, shared, or high-data-access accounts, then move to low-risk users and low-value applications. The most dangerous cases are the ones that look operationally harmless but can reach sensitive mailboxes, documents, or admin surfaces.

Common mistake: Treating App Passwords as a user convenience feature instead of a temporary compatibility control. That mindset tends to produce weak ownership, no expiry discipline, and poor visibility into where the secret is stored.

Practitioner takeaway: The key judgement is to manage App Passwords as temporary exception secrets, not as an acceptable long-term sign-in method, and to retire them as soon as the legacy dependency disappears.

Related resources from NHI Mgmt Group

• How can security and finance teams work together on app deprovisioning?
• How should security teams handle app-specific passwords when they use passkeys or MFA?
• Why do app-specific passwords create risk even when they are limited to legacy apps?
• How do IAM and mobile security teams work together on app governance?