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Portal Walkthrough: Control 1.26 - Agent File Upload and File Analysis Restrictions

Last Updated: April 2026 Portals: Copilot Studio, Power Platform Admin Center (PPAC), Microsoft Purview, Microsoft Defender XDR (Zone 3) Estimated Time: 20–40 minutes per agent (Zone 3 includes DLP and content-scanning verification)

Prerequisites

  • AI Administrator (canonical role per docs/reference/role-catalog.md) — primary owner for the per-agent File Upload toggle and allowed-file-type list
  • Power Platform Admin — required for environment feature flags, SharePoint Embedded (SPE) container review, and DLP scope
  • Purview Compliance Admin — required for DLP and sensitivity-label policy verification (Zone 2+)
  • Copilot Studio Agent Author (Environment Maker + agent ownership) — required to open agent Settings
  • Documented governance-zone classification for each target agent (Zone 1 / Zone 2 / Zone 3)
  • Approved file-upload enablement request with documented business justification (Zone 2+); formal risk assessment (Zone 3)
  • Companion: Control 1.25 (MIME Type Restrictions) implemented at the environment level — this control is per-agent and depends on environment-level allowlists for defense-in-depth

Scope note: This walkthrough governs the per-agent File Upload toggle in Copilot Studio. Environment-wide file-type and MIME allowlists are governed by Control 1.25. Apply both for layered protection.

Step-by-Step Configuration

Step 1: Confirm Agent Zone Classification and Approval State

  1. Open your agent inventory and confirm the agent's governance zone (1 / 2 / 3)
  2. For Zone 2 or Zone 3 agents, confirm an approved file-upload enablement request exists in your governance system of record (ServiceNow, SharePoint List, Dataverse, etc.)
  3. For Zone 3 agents, confirm a documented risk assessment is on file and approved by the AI Governance Lead or designate

Important: Do not toggle File Upload on for a Zone 2 or Zone 3 agent without the documented approval. Toggle changes are recorded in the Power Platform admin activity log and may surface during supervisory review.

Step 2: Open the Per-Agent Security Panel (Copilot Studio)

  1. Open Copilot Studio
  2. Select the target environment from the environment switcher (top-right)
  3. Open the target agent
  4. Click the agent name → Settings → Security

Portal path (April 2026): Copilot Studio → [Environment] → [Agent] → Settings → Security → File Upload. The Security node is reached from the per-agent Settings panel; older guidance that lists a Knowledge sub-tab for the toggle is stale.

Step 3: Set the File Upload Toggle Per Zone

Zone Recommended Default Conditions to Enable
Zone 1 (Personal) On acceptable for personal-productivity use None beyond Microsoft defaults; periodic review
Zone 2 (Team) Off until approved Documented approval and DLP coverage in the agent's environment
Zone 3 (Enterprise) Off (default deny) Formal risk assessment, AI Governance Lead approval, DLP enforce mode, and Defender content scanning
  1. Toggle File Upload to the state determined by Step 1's approval check
  2. Click Save
  3. Republish the agent: Copilot Studio caches agent runtime configuration; the new toggle state may not be enforced for clients until the agent is republished

Step 4: Configure Allowed File Types (Per-Agent Allowlist)

Required for every Zone 2 and Zone 3 agent with File Upload = On. PPAC controls (Control 1.25) establish the maximum permitted file types for the environment; per-agent allowlists apply additional least-privilege restrictions.

  1. In the File Upload section, locate Allowed file types (visible only when the toggle is On)
  2. Reduce the allowlist to the minimum set required by the agent's documented purpose
  3. Example: a contract-summary agent → .pdf only
  4. Example: a financial-analysis agent → .xlsx, .csv only
  5. Do not inherit the full environment allowlist by default
  6. Click Save and republish

Step 5: Verify File Size and Per-Conversation Limits

  1. Review and document the Microsoft-defined limits applicable to your agent (per Microsoft Learn, April 2026):

    Source Limit
    Maker-uploaded knowledge files Up to 512 MB per file
    Knowledge files per agent (local upload) 500 files (GA Aug 2025)
    Knowledge files per agent (SharePoint/OneDrive source) 1,000 files (GA Aug 2025)
    User-uploaded PDF at runtime <40 pages
    User-uploaded TXT/CSV at runtime <180 KB
    User-uploaded image at runtime 15 MB (4 MB on Direct Line)

  2. For Zone 3, document any organizational reductions to these defaults (e.g., enforced via Defender for Cloud Apps file size policies) in the risk assessment

Note: Microsoft does not currently expose a per-agent setting to lower these defaults below platform values. Reductions must be enforced via complementary controls (Defender file policies, Purview DLP rules, network egress policies).

Step 6: Verify Sensitivity Label Inheritance

  1. In Copilot Studio, navigate to the agent's Knowledge section
  2. If File Upload is On, upload a small test file with a sensitivity label applied at source (e.g., Confidential)
  3. Confirm the agent surfaces the inherited label in the agent properties panel
  4. Upload a second test file with a more restrictive label (e.g., Highly Confidential) and verify the agent inherits the most restrictive label
  5. Capture screenshot evidence and store under maintainers-local/tenant-evidence/1.26/ (gitignored)

Caveat: Auto-labeling for SharePoint Embedded (SPE) containers used by Copilot Studio may require an explicit Purview auto-labeling policy that includes the SPE location. If labels do not flow through, see the Troubleshooting playbook.

Step 7: Verify DLP Policy Coverage (Zone 2+)

  1. Open Microsoft Purview → Data Loss Prevention → Policies
  2. Confirm a DLP policy exists that covers the Power Platform location and is scoped to the agent's environment
  3. Confirm the policy is in Enforce mode (not Test or Off)
  4. For Zone 3, confirm the policy includes the FSI-relevant Sensitive Information Types (US SSN, US Bank Account Number, Credit Card Number, ITIN, MNPI patterns) and configures Block action with override prohibited

Step 8: Configure Defender for Cloud Apps Content Scanning (Zone 3)

Required for Zone 3. PPAC and per-agent allowlists inspect declared file extensions and MIME headers; magic-byte (true content type) inspection requires Defender for Cloud Apps. See Control 1.25 portal walkthrough Step 7 for the parallel environment-level pattern; this step targets the agent's SPE container.

  1. Open Microsoft Defender XDR portal → Cloud apps → Policies → Policy management → File policy
  2. Create a file policy scoped to SharePoint Online / OneDrive for Business that filters on the SPE container associated with the agent's environment
  3. Add filter: MIME type (true type) does not equal the approved per-agent allowlist
  4. Governance actions: Quarantine + Notify file owner + Notify SOC distribution list
  5. Create a High severity alert; forward to Microsoft Sentinel
  6. Save and confirm the policy is Enabled

Step 9: Review SharePoint Embedded Container Configuration

  1. Open Power Platform Admin Center → Environments → [Environment]
  2. Locate the SharePoint Embedded container details for the environment hosting the agent
  3. Document the container ID and verify:
  4. Access controls limit the container to authorized service principals and admins
  5. A Purview retention policy is applied (Zone 2+) that meets the agent's record-retention obligations under FINRA 4511 / SEC 17a-4(f)
  6. Container auditing is enabled (Zone 2+)
  7. Capture the configuration as JSON evidence (see PowerShell Setup for SHA-256 evidence emission)

Step 10: Update the Per-Agent Inventory

  1. Update the file-upload inventory with:
  2. Agent name and environment
  3. Zone classification
  4. Toggle state and allowed-file-type list
  5. Approval reference (ticket / record ID)
  6. Last review date and reviewer
  7. Schedule the next review at the zone-appropriate cadence (Zone 1 quarterly / Zone 2 monthly / Zone 3 weekly)

Configuration by Governance Level

Setting Baseline (Zone 1) Recommended (Zone 2) Regulated (Zone 3)
File Upload toggle default Allowed Disabled until approved Default deny
Per-agent allowed file types Microsoft defaults Reduced to documented purpose Minimum set; documented in risk assessment
Approval required No Documented approval Formal risk assessment + AI Governance Lead approval
Sensitivity label inheritance Recommended Required Required with audit trail
DLP policy coverage Not required Required (Enforce mode) Required + content scanning
Defender for Cloud Apps content scanning Not required Optional Required (true-MIME inspection)
SPE container retention policy Recommended Required Required + auditing enabled
Sentinel monitoring Optional Optional Required
Inventory tracking Recommended Required Required
Review frequency Quarterly Monthly Weekly
Exception process Informal Documented Documented with approval

Validation

After completing these steps, verify:

  • Per-agent File Upload toggle state matches the agent's zone and approval status
  • Per-agent Allowed file types list is reduced to the minimum required by the agent's documented purpose (Zone 2+)
  • Sensitivity-label inheritance test passes (agent surfaces the most restrictive label from uploaded files)
  • DLP policy in Enforce mode covers the agent's environment (Zone 2+)
  • Defender for Cloud Apps file policy with true-MIME inspection is Enabled (Zone 3)
  • SPE container access controls, retention policy, and auditing are configured (Zone 2+)
  • Per-agent inventory updated with toggle state, approval reference, and next review date
  • Screenshot evidence captured under maintainers-local/tenant-evidence/1.26/ (gitignored — never push to the repository)

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