SharePoint auto-sync can turn local files into tenant-wide secret exposure

At a glance

What this is: This analysis shows how OneDrive auto-sync and SharePoint can turn ordinary local files into tenant-wide secret exposure.

Why it matters: It matters because IAM, IGA, and NHI teams have to govern where secrets live, who can see them, and how cloud sync changes the blast radius of compromised accounts.

By the numbers:

• The OneDrive sync client is enabled by default on Windows 10 and 11, according to Entro Security research.

Context

OneDrive auto-sync is a file governance problem as much as a storage convenience feature. When Desktop and Documents are silently moved into SharePoint-backed libraries, the organisation loses the assumption that secrets stay bounded to a workstation or a named owner.

The article's core finding is that this normalised sync path can turn plaintext secrets in .env files, config files, spreadsheets, and scripts into broadly accessible tenant data. That shifts the control question from simple endpoint hygiene to identity-aware data access governance across Microsoft 365.

For IAM and NHI programmes, the issue is not whether a secret was intentionally shared. It is whether a sync path converted a local file into an enterprise-readable object before security teams ever had a chance to classify or restrict it.

Key questions

Q: What breaks when local files are auto-synced into SharePoint?

A: The assumption that workstation files remain workstation-bound breaks first. Auto-sync moves sensitive local content into a cloud repository with broader visibility, central search, and administrative access, so a secret stored for convenience can become tenant-readable without deliberate sharing.

Q: Why does SharePoint auto-sync increase the blast radius of a compromised account?

A: Because the account no longer protects only email or SaaS access. If the user’s synced folders contain secrets, the compromise can expose credentials, tokens, and config files that unlock other systems, turning one identity failure into multiple downstream compromises.

Q: What signs suggest synced file repositories are becoming a secrets problem?

A: Look for a growing volume of .env, .json, .pem, .xlsx, and script files in SharePoint-backed libraries, especially when those files contain token, password, or key keywords. A rising hit rate means users are treating collaboration storage as a secrets vault.

Q: Should security teams disable OneDrive auto-sync by default?

A: They should disable or restrict it where the business does not need continuous folder backup. If the organisation keeps the feature, it should be paired with policy controls, user awareness, and secret scanning. The decision depends on risk tolerance, but default enablement without governance is a poor control posture for sensitive environments.

Technical breakdown

How KFM turns local folders into cloud-readable content

OneDrive Known Folder Move, or KFM, redirects common user folders such as Desktop and Documents into OneDrive. In enterprise deployments, those files are stored in SharePoint Online document libraries, where they inherit the platform's permission and administration model. That means a file that feels local to the user is no longer governed as a workstation artefact; it becomes cloud content with administrative visibility. The technical problem is not malware or exploit code. It is the automatic relocation of sensitive material into a collaboration system that was never asked to distinguish a harmless document from a secrets-bearing file.

Practical implication: treat sync paths as data exposure controls, not just user productivity settings.

Why synced files become tenant-wide exposure

Once files land in SharePoint, the access model is no longer limited to the original file owner. The article notes that administrators can elevate themselves to site collection administrator and then read synced files directly, while compromised identities can search across the tenant. This creates a broad read surface for secrets that were never meant to leave a desktop. Searchability matters here because indexable file repositories turn scattered secrets into a centrally mineable corpus. That is what transforms casual local storage into a secrets-discovery problem at tenant scale.

Practical implication: review which identities can search, administer, and enumerate synced repositories.

Why common secret formats are especially dangerous in sync ecosystems

The article highlights that spreadsheets, text files, JSON, PEM files, scripts, and documents often contain secrets because users store credentials where work happens. These formats are dangerous in sync ecosystems because they are lightweight, easy to move, and easy to share, so they propagate without the friction that code repositories or CI systems sometimes impose. A .env file on a desktop can become a SharePoint object with broad visibility before anyone labels it as sensitive. That makes file type alone an unreliable control boundary.

Practical implication: classify and scan synced user files as potential secret stores, not benign collaboration content.

Threat narrative

Attacker objective: The attacker aims to mine synced files for reusable secrets that unlock broader enterprise systems and expansion paths.

1. Entry occurs when a user stores a secret in a local file such as .env, passwords.xlsx, or a config fragment on Desktop or Documents and OneDrive KFM silently syncs it to SharePoint-backed storage.
2. Credential access expands when an administrator, compromised account, or tenant-wide search query retrieves the synced file from SharePoint or through Microsoft 365 administration.
3. Escalation follows when the secret grants access to downstream systems such as Slack, cloud APIs, or other internal services beyond the original workstation.
4. Impact is tenant-wide exposure of secrets that were assumed to be local, enabling lateral movement and further account compromise across the Microsoft 365 estate.

Breaches seen in the wild

• MongoBleed breach: MongoBleed exposed secrets across 87K MongoDB servers.
• Shai Hulud npm malware campaign: Shai Hulud campaign: npm malware exposed secrets on GitHub.

Read our 52 NHI Breaches Analysis report for a comprehensive view of breaches impacting Non-Human Identities including AI Agents.

NHI Mgmt Group analysis

Auto-sync creates trust debt in file governance: The organisation assumes that local files remain locally bounded until a user deliberately shares them, but OneDrive KFM breaks that premise by moving content into a tenant-managed collaboration layer. That means the governance problem begins before sharing and before incident response. Practitioners need to treat automatic sync as a trust boundary change, not a convenience setting.

Tenant visibility is the real exposure multiplier: Once a secret is indexed in SharePoint, the risk is no longer limited to the original file owner or device. Administrators, over-privileged accounts, and tenant-wide search capabilities can surface material that users believed was private. The result is an identity-enabled discovery problem, not just a storage issue, and that widens the blast radius of every compromised account.

Shared-file convenience and secrets hygiene are now coupled: Collaboration platforms absorb files from desktops, team chats, and personal folders, but the security model rarely differentiates a slide deck from a credential note. That gap creates a named concept worth tracking: sync-to-secrets amplification. The implication is that governance must account for file provenance and sync behaviour, not only content ownership.

Endpoint-local secrets are no longer a safe assumption: The traditional advice to keep secrets off code and in local environment files only reduces one risk path. It fails when automatic backup quietly places those files into a cloud repository with broad administrative access. The practical conclusion is that lifecycle and access governance must extend to sync destinations, not stop at the device boundary.

Credential searchability is an operational weak point: The article shows that simple keyword searches and automated scanners can surface API keys and tokens once files are centralised in SharePoint. That turns large file stores into discovery engines for attackers and over-privileged insiders alike. Security programmes should assume that any indexable secret store becomes a queryable attack surface.

From our research library:

• 91.6% of secrets remain valid five days after the targeted organisation is notified, showing a critical gap in remediation procedures, according to the Ultimate Guide to NHIs.
• Read next: Top 10 NHI Issues

What this signals

Sync-to-secrets amplification: automatic file backup is now an identity risk multiplier because it changes where secrets live and who can discover them. Programmes that still treat local files as outside IAM scope will miss the access layer that sync creates, especially when collaboration storage is searchable by privileged users.

The practical shift is to govern file provenance and destination together. If a developer or contractor stores credentials in a local working file, the risk does not end on the endpoint once KFM is enabled, so SharePoint scanning and sync-policy review need to sit inside the same operating model.

For practitioners

• Disable or restrict KFM where it is not required Review whether Desktop and Documents need to sync at all. If not, block OneDrive Known Folder Move through policy so local files do not automatically become SharePoint content.
• Harden Microsoft 365 admin paths Limit who can elevate to site collection administrator and who can search across synced libraries. Broad tenant visibility turns a single exposed file into a discovery event.
• Scan collaboration storage for secrets Extend secrets detection to SharePoint, Teams-linked libraries, and synced user folders. Code scanning alone misses the file types most often used for quick credential storage.
• Warn developers and contractors about sync behaviour Make it explicit that local .env files, config fragments, and spreadsheets may leave the device automatically. Awareness needs to cover employees, contractors, and third parties who store secrets in personal working files.

Key takeaways

• OneDrive auto-sync can quietly convert local working files into enterprise-readable secret stores, which makes convenience settings part of the identity security surface.
• Entro Security reports that SharePoint accounts for one in five exposed enterprise secrets, and that scale shows why storage-only thinking misses the governance failure.
• The most effective control point is before sync and indexing, where policy, admin scope, and secrets scanning can stop local files from becoming tenant-wide exposure.

Key terms

• Known Folder Move: A OneDrive feature that automatically redirects common user folders such as Desktop and Documents into cloud storage. In security terms, it can convert files that appear to be local into centrally accessible content, which changes the exposure model for secrets and other sensitive data.
• Sync-to-Secrets Amplification: Sync-to-secrets amplification describes the way routine file synchronisation increases the discovery and exposure of embedded credentials. A file that was low risk on a workstation can become high risk once it is indexed, searchable, and accessible through collaboration or administration paths.
• Tenant-Wide Exposure: Tenant-wide exposure occurs when a compromise or misused privilege affects more than one account and can reach many users or resources in a cloud directory. In OAuth abuse, an administrator or overprivileged user may grant an app access that extends beyond a single mailbox to the entire Microsoft 365 tenant.
• Secret-Bearing File: A file that stores credentials, tokens, keys, or other authentication material needed by software or operators. In practice, .env files are a common example because they are convenient for developers but risky when tools read them without explicit permission or containment.

Deepen your knowledge

NHI governance, identity lifecycle, and secrets management are core topics in our NHI Foundation Level course, the industry's only accredited NHI security programme. If you are building or maturing an IAM programme, it is worth exploring.