Copilot Security & Oversharing Scorecard

An ethical hacker or rogue employee runs a simple Graph API query search for keywords like salary, layoff, or M&A. Because SharePoint site owners lazily added EEEU to site members, Copilot indexes these files. When the employee prompts Copilot: "What are the salaries of executives?", Copilot synthesizes the leaked spreadsheets.

# Remove Everyone Except External Users from a SharePoint site
$SiteURL = "https://yourtenant.sharepoint.com/sites/SensitiveData"
Connect-PnPOnline -Url $SiteURL -Interactive
$Group = Get-PnPGroup -AssociatedMemberGroup
Remove-PnPUser -LoginName "c:0-.w|s-1-5-21-..." -Group $Group

Without Purview encryption, any file extracted via custom SPFx plugins or read by Copilot remains raw text. A hacker who gains access to a user account can extract whole knowledge libraries because standard SharePoint boundaries are soft. Enforced label encryption shields the file payload on disk and inside downstream client buffers.

# Set automatic Purview labeling rules for sensitive SSN/PII keywords
Set-DlpCompliancePolicy -Identity "PII-Data-Protection" -Enabled $true
Set-DlpComplianceRule -Identity "Encrypt-SSN" -ContentContainsSensitiveInformation @(@{Name="U.S. Social Security Number (SSN)"; MinCount=1})

If an administrator has accidentally shared the executive site collection, standard search algorithms and Copilot index bots ingest the site. RSA establishes a hard-coded security fence restricting access specifically to a designated Microsoft 365 security group, completely neutralizing accidental link clicks.

# Restrict site access using SPO Advanced Management
Set-SPOSite -Identity "https://tenant.sharepoint.com/sites/ExecutiveBoard" -RestrictedAccessBySecurityGroup $true
# Add security groups permitted to access site
Set-SPOSite -Identity "https://tenant.sharepoint.com/sites/ExecutiveBoard" -AddRestrictedAccessSecurityGroupId "00000000-0000-0000-0000-000000000000"

When users hit "Share" to copy a link, they default to "People in my organization with the link". These links can easily leak into Teams channels, calendar events, or email chain histories. Copilot intercepts these broad URLs, immediately adding them to its global semantic cache for all users in that chain.

# Set default sharing links to Specific People (most secure client-side default)
Set-SPOTenant -DefaultSharingLinkType Internal
Set-SPOTenant -DefaultSharingLinkPermission View

An attacker with a guest account can exploit lax sharing controls to reshare tenant folders with personal Outlook or Gmail accounts. Because the tenant does not enforce "Specific Domain" policies, the guest issues outbound access grants, exfiltrating document directories undetected.

# Restrict tenant external sharing to specific allowed domains only
Set-SPOTenant -SharingCapability ExternalUserAndGuestSharing
Set-SPOTenant -SharingDomainRestrictionMode AllowList -SharingAllowedDomainList "partner1.com, partner2.com"

Consent phishing is a critical exploit vector. An attacker creates a fake utility app (e.g. "PDF Converter") and emails a user to sign in using their work account. The user accepts the permissions dialog. The rogue application immediately steals OAuth refresh tokens, scraping entire SharePoint lists via Microsoft Graph in the background.

# Disable user consent for enterprise apps in Entra ID
az ad policy user-consent-flow update --id "Default" --enable $false
# Force admin consent workflow to review permissions centrally

Attackers scan GitHub repositories or local user files for leaked tenant application secrets. If they discover a client secret for a registered app with Sites.Read.All, they can query the tenant's entire SharePoint database directly from external terminal systems without triggering MFA alerts.

# Audit all service principals with highly privileged roles
az ad app permission list --id "00000000-0000-0000-0000-000000000000"
# Instantly revoke expired client secrets to secure tenant

Attackers upload malicious macros disguised as PDF contracts directly to external SharePoint directories. When an internal HR manager accesses the file, it executes local shell exploits. Safe Attachments automatically opens files inside a virtual cloud container, neutralizing the payload before execution.

# Enable Microsoft Defender protection rules for SharePoint and OneDrive
Set-AtpPolicyForO365 -EnableATPForGD $true -TrackAndDownload $true

To export data without triggering DLP alerts, users try to shift labels from Confidential-Internal to Public. Enabling mandatory justification logs this action to Microsoft Purview's unified audit log, prompting immediate SIEM escalation on unusual batch shifts.

# Force users to provide justification before downgrading labels
Set-LabelPolicy -Identity "Global-Data-Policy" -DowngradeSensitivityLabelJustificationRequired $true

A permanent SharePoint administrator account gets compromised via password spraying or session hijacking. Because the account holds permanent admin tokens, the attacker immediately modifies tenant sharing parameters. Gating admin privileges behind PIM restricts active session duration and mandates approval.

# Set up JIT administrative activation window limits in PIM
Set-AzureADMSPrivilegedRoleSetting -ProviderId "aadRoles" -Id "SharePoint Service Administrator" -MaxDurationInHours 2 -MfaRequired $true