Because the permission often outlives the upload. Once an app has broad read access and a usable token, it can keep reaching into OneDrive beyond the original task, which turns a one-time file exchange into an ongoing exposure path for sensitive content.
Why delegated file access is riskier than a normal upload
A normal upload is usually a bounded transaction: the user gives one file, the app processes it, and access ends. Delegated file permissions change that shape. The app is no longer holding a single object, it is holding a reusable access path, often with read scope that can reach beyond the original upload and persist until the token or consent is revoked.
That matters because the security boundary shifts from “this file was shared” to “this app can keep returning to the user’s storage.” If the delegated permission is broad enough, the app can enumerate folders, reopen older content, or silently retain access to future files without another user action.
In practice, the risk is not just that one document is exposed. The risk is that the permission becomes a standing retrieval channel into a live content store, which is a very different trust model from a one-off upload endpoint.
What makes the exposure persistent instead of one-time
Delegated access is powerful because it combines token exchange and delegation mechanics with stored consent or a durable refresh path. Once the app has a usable token, it may be able to act again later without the user being present, so the original approval effectively outlives the immediate task.
That persistence is amplified when the app also receives broad read scope. A narrow upload flow only needs the file the user selected. A delegated flow can become an ambient access relationship, which creates a larger blast radius if the app is compromised, over-permissioned, or simply built to collect more than it needs.
This is why OWASP Non-Human Identity Top 10 treats secret sprawl, overprivilege, and long-lived access as core failure patterns: the problem is not the upload itself, but the durable authority behind it. The same logic appears in NHIMG guidance on privileged access management, where access should be bounded, reviewable, and revocable rather than left as a standing entitlement.
Why broad delegated permissions expand the attack surface
Once an app can reach beyond a single file, the attack surface includes every file location and every future token use. A malicious or compromised app does not need to wait for another upload if it can keep reading the user’s storage directly. That turns permission scope into a data-exposure problem, not just an application-input problem.
Broad delegated access also makes abuse harder to notice. The user may have approved a legitimate task, but the same permission can later support bulk collection, targeted search across sensitive folders, or quiet exfiltration of content that was never intended for the original workflow. The permission-aware retrieval model is a useful comparison here: if access controls are not enforced at the point of use, oversharing follows naturally.
The practical distinction is that upload flows normally expose only what the user deliberately submits. Delegated read flows expose what the user can see, now and later, which means the app inherits the user’s entire reachable content boundary unless permissions are tightly constrained.
Risk and Threat Considerations
Broad delegated file permissions create exposure in two directions, they can overreach during normal operation and they can be abused after compromise. The most serious failure mode is scope creep: an app approved for one task quietly gains standing access to a much larger content set than the user expected.
Failure mechanism: The app receives durable delegated read authority, then keeps using that authority to enumerate, reopen, or export files beyond the original upload event. If the token, consent grant, or app identity is compromised, the same path becomes a direct exfiltration channel.
Impact: Sensitive content can be collected without repeated user approval, making a single overbroad grant much more damaging than a one-time upload. In a large environment, that also increases lateral exposure across folders, users, and shared content sets.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 addresses the attack and risk surface, while NIST SP 800-53 Rev 5 and NIST SP 800-63 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-07 — Long-Lived Secrets | Broad delegated access often persists via durable tokens and consent. |
| NHI-05 — Overprivileged NHI | Broad file permissions create excess read scope beyond the upload need. | |
| NHI-10 — Human Use of NHI | User-approved delegation can be reused beyond the original human intent. | |
| Recommendation — Limit token lifetime and revoke delegated access as soon as the task ends. Restrict delegated file access to the minimum files and folders required. Ensure delegated access cannot be repurposed outside the user-approved workflow. | ||
| NIST SP 800-53 Rev 5 | IA-5 — Authenticator Management | Delegated file access depends on managing token lifecycle and revocation. |
| AC-6 — Least Privilege | The risk is excessive file scope compared with the task actually needed. | |
| AC-2 — Account Management | Delegated access should be reviewable and removable when no longer needed. | |
| Recommendation — Enforce short-lived credentials and revoke unused delegated tokens promptly. Constrain file permissions to the minimum access required for the use case. Review and remove stale delegated access paths on a defined schedule. | ||
| NIST SP 800-63 | Digital Identity Guidelines | Delegated flows rely on authenticator and token trust, especially for durable access. |
| Recommendation — Use strong reauthentication and short session lifetimes for sensitive delegated access. | ||
Practitioner Guidance
What to verify: Check whether the app truly needs read access to storage, or only needs the uploaded object and nothing else. If the use case is submission or processing, prefer file-scoped or task-scoped access and treat folder-wide or mailbox-wide permission as an exception.
Decision rule: If a delegated permission can survive the original task, rotate or revoke it quickly and design for the smallest possible access window. If the app must retain access, require a clear business justification, explicit owner approval, and periodic review of the actual files it can reach.
Practitioner takeaway: The core question is not whether the upload was authorized, but whether the permission can be reused in ways the user did not intend. The more reusable the access path, the more it behaves like standing privilege rather than a simple file transfer.
Related resources from NHI Mgmt Group
- Why do broad cloud file-picker permissions create a higher risk for sensitive data than many users realise?
- Why do non-human identities create more audit risk than human accounts?
- Why do non-human identities create audit risk in modern environments?
- Why do non-human identities create compliance risk even when policies exist?