Why do unmonitored service accounts and tokens increase risk in Microsoft 365 environments?

Unmonitored service accounts and tokens create persistent trust paths that attackers can abuse without triggering normal user controls. When those identities have broad permissions, a single compromise can expose mail, files, or admin settings across connected applications. The risk grows when access is inactive, overprivileged, or tied to non-marketplace apps that were never rigorously vetted.

Why This Matters for Security Teams

Unmonitored service accounts and tokens are risky because Microsoft 365 treats them as durable trust anchors, not as temporary user sessions. Once issued, they can keep working long after the original owner has changed roles, left the company, or lost oversight. That creates a hidden access layer that bypasses the review, MFA prompts, and conditional checks security teams rely on for human identities.

This is not just an administration gap. The Top 10 NHI Issues research and the 2024 ESG Report: Managing Non-Human Identities both show how often non-human identities are under-governed, and how frequently compromised NHIs lead to successful attacks. In Microsoft 365, that matters because one stale token can reach mailboxes, SharePoint, Teams, and connected SaaS apps through delegated permissions or app consent.

Security teams often assume that if a token was created for a legitimate app, the risk is bounded. In practice, many organisations discover the exposure only after an inbox rule, mailbox export, or OAuth abuse has already occurred.

How It Works in Practice

In Microsoft 365, risk grows when service principals, OAuth grants, refresh tokens, and app registrations are left outside normal identity hygiene. A token may be valid for minutes, but a refresh token, certificate, or application secret can extend access far longer. If that identity has broad Graph API permissions, an attacker who steals it can move quietly through data and admin surfaces without needing interactive login.

Current guidance suggests treating these identities as workloads, not as “background accounts.” That means inventorying every service principal, mapping what each token can do, and tying each permission to an owner, purpose, and expiration. The control objective is least privilege plus continuous review, consistent with NIST Cybersecurity Framework 2.0 and NIST SP 800-53 Rev. 5.

Practitioners should also separate routine automation from high-impact access. For example:

• Use just-in-time access for privileged automation instead of permanent mailbox or tenant admin rights.
• Prefer short-lived secrets and certificate rotation over static client secrets that rarely change.
• Review app consent and delegated permissions, especially for non-marketplace apps and shadow IT integrations.
• Alert on anomalous token use, unusual Graph scopes, and service accounts that authenticate outside expected job schedules.

The most useful mental model is that a token is not just a credential, it is an execution path. The Salesloft OAuth token breach and the Microsoft OAuth Breach both illustrate how trusted integrations become high-value targets when access is not continuously monitored. These controls tend to break down in tenants with large legacy app inventories because ownership, scope, and expiry data are incomplete or missing.

Common Variations and Edge Cases

Tighter token governance often increases operational overhead, requiring organisations to balance automation reliability against stricter expiration, approval, and rotation controls. That tradeoff is especially visible in Microsoft 365 environments that rely on legacy daemon apps, scheduled jobs, or line-of-business systems that cannot tolerate frequent credential churn.

There is no universal standard for this yet, but current guidance suggests different handling for different trust levels. A low-risk reporting app should not be treated like a tenant-wide mail processor. Similarly, a service account used for one SaaS connector should not inherit the same visibility or access path as a privileged provisioning workflow. Where possible, keep the blast radius small by splitting functions into separate identities.

One common edge case is app-only access that looks safe because no human password exists. That can still be dangerous if the app secret, certificate, or refresh token is long-lived and stored in a poorly governed vault or pipeline. Another edge case is delegated access granted to a benign-looking productivity tool that later expands its scopes or is abandoned without removal. The Guide to the Secret Sprawl Challenge is relevant here because secrets sprawl often outlives the business need that created it.

In mature Microsoft 365 environments, the best outcome is not zero tokens. It is visible, owned, time-bounded access that can be reviewed, revoked, and explained quickly when behaviour changes.

Related resources from NHI Mgmt Group

• Why do service accounts and OAuth tokens increase breach impact in cloud environments?
• Why do service accounts and secrets with standing access increase risk in cloud environments?
• Why do service accounts increase lateral movement risk in enterprise environments?
• Why do service accounts increase risk in cloud and legacy environments?