Information Sharing

To meet the FedRAMP information sharing requirement (NIST SP 800-53 Rev. 5 AC-21), you must give authorized users a reliable way to confirm that a third party’s access permissions match the data’s sharing rules before data is shared. Operationalize this by defining sharing “circumstances,” tagging data with restrictions, mapping partner entitlements to those restrictions, and retaining approvals plus periodic revalidation evidence. ¹

Key takeaways:

• Define “information sharing circumstances” and data restrictions in a way your systems can enforce and your teams can audit. ¹
• Implement a pre-share authorization check that compares the sharing partner’s entitlements to the information’s access and use restrictions. ¹
• Keep durable evidence: requests, approvals, provisioning records, reviews, and exceptions tied to each sharing pathway. ¹

AC-21 is easy to misunderstand because it is not a generic “share securely” statement. It is a specific operator requirement: for defined sharing scenarios, authorized users must be able to determine whether a sharing partner’s access authorizations match the information’s access and use restrictions. ¹

For a FedRAMP cloud service offering, this lives in the day-to-day mechanics of how your teams grant external access, publish data to customer-controlled tenants, provide agency exports, connect to partner systems, or allow support staff and subcontractors to handle federal information within the authorization boundary. If your answer to “how do you know the recipient is allowed to receive this exact dataset in this exact way?” is tribal knowledge, AC-21 will hurt during assessment testing and continuous monitoring because you will struggle to show a repeatable control with evidence. ¹

This page translates AC-21 into a concrete implementation pattern: define the sharing situations, label information with restrictions, implement an entitlement check that authorized users can perform (or that the system performs with an auditable decision record), then review and revoke when conditions change. ¹

Regulatory text

Control requirement (AC-21): “Enable authorized users to determine whether access authorizations assigned to a sharing partner match the information's access and use restrictions for organization-defined information sharing circumstances.” ¹

What the operator must do:
You must (1) define the circumstances under which information is shared, (2) define the access and use restrictions that apply to the information in those circumstances, and (3) provide a mechanism so an authorized user can confirm the sharing partner’s authorizations align with those restrictions before sharing occurs. The mechanism can be technical (policy engine, IAM checks, data-sharing workflow gates) or procedural with strong records, but it must be repeatable and testable. ¹

Plain-English interpretation

AC-21 requires “permission matching” at the moment of sharing. You are not only controlling internal user access; you are controlling what happens when information crosses a boundary to another party (agency, contractor, integrator, customer, support subcontractor, or other third party) under defined scenarios. ¹

Think of it as answering three questions consistently:

1. What are we sharing and what restrictions apply to that information?
2. Who is the sharing partner and what authorizations do they have?
3. Do those authorizations satisfy the restrictions for this specific sharing circumstance? ¹

Who it applies to

Entities

• Cloud Service Providers (CSPs) operating within a FedRAMP authorization boundary implementing the FedRAMP Moderate baseline. ¹
• Federal agencies responsible for maintaining the authorized baseline and overseeing sharing involving the system. ¹

Operational context (where AC-21 shows up)

AC-21 is implicated whenever information is shared with or made accessible to a sharing partner, including:

• Cross-tenant sharing or data replication where another organization can access data.
• Agency-requested exports, reports, or bulk extracts.
• Support and troubleshooting access by third-party personnel within the boundary.
• Integrations that push or pull data to/from a partner environment (APIs, file transfers, connectors).
• Collaborative features that allow another entity to view, download, or act on data. ¹

What you actually need to do (step-by-step)

Step 1: Define “information sharing circumstances”

Create a short list of sanctioned sharing scenarios and treat them like controlled pathways. Examples (adapt to your system):

• “Agency-to-agency sharing via exported report”
• “Third-party support access for break/fix”
• “Partner API integration for case routing”
• “Customer-managed user invited into a tenant” ¹

For each circumstance, specify:

• Allowed data types / categories
• Allowed actions (view, export, download, write, delete)
• Allowed destinations (which parties, which systems, which tenants)
• Approval roles required (data owner, system owner, security, agency) ¹

Deliverable: an “Information Sharing Circumstances Register” that is referenced by policy and runbooks.

Step 2: Define access and use restrictions in enforceable terms

Restrictions must be something you can check. Translate narrative requirements into fields and rules:

• Data classification / sensitivity tags
• Handling requirements (e.g., “no external download,” “US persons only,” “must remain in boundary-approved storage”)
• Purpose limitations (“support only,” “contract performance only”)
• Time bounds (access start/end, emergency access expiry)
• Redistribution limits (no onward sharing without approval) ¹

If your restrictions are only in a PDF policy, you will fail the “determine whether” intent because there is nothing consistent to compare against.

Deliverable: a data tagging standard plus a mapping table from tag → allowed sharing circumstances.

Step 3: Build the “authorization matching” mechanism

AC-21 does not require a specific tool, but it does require a dependable method that an authorized user can use to verify match.

Common implementation patterns:

• Workflow gate: a ticket/workflow where the request includes data tags + sharing circumstance, and an approver confirms the sharing partner’s entitlements align before provisioning/export occurs.
• Policy-as-code / entitlement check: a rules engine evaluates (data restrictions, circumstance, partner attributes, requested actions) and produces an allow/deny with an audit log entry.
• IAM group mapping: partner identities are placed into roles/groups that correspond to permitted circumstances, and the sharing action checks role membership and data tags before allowing the share. ¹

Minimum bar for auditors: you can show how an authorized user (or system on their behalf) checks that the partner’s assigned authorizations match the information’s restrictions for that circumstance, and you can show records of those checks. ¹

Deliverable: a documented “pre-share check” with screenshots, system logs, or workflow steps.

Step 4: Provision access with least privilege and traceability

Once the match is confirmed, provision only what is required:

• Scope to specific datasets, tenants, or objects.
• Grant only the actions needed.
• Prefer time-bound access where feasible.
• Record who approved, who provisioned, what changed, and where it applies. ¹

Deliverable: provisioning runbook + change records (IAM change logs, tickets, access request approvals).

Step 5: Revalidate and revoke on triggers

AC-21’s risk is persistent inappropriate access after conditions change. Define revocation triggers and implement reviews:

• Contract end or support engagement closure
• Personnel changes at the sharing partner
• Sharing circumstance no longer applies
• Data reclassification or restriction changes
• Integration decommissioning ¹

Deliverable: periodic access review evidence and a documented revocation process.

Step 6: Handle exceptions without breaking the control

If you allow exceptions (“urgent export,” “one-time access”), require:

• Explicit exception approval and scope
• Compensating controls (extra logging, limited duration)
• Post-event review and closure ¹

Deliverable: exception register entries tied to the circumstance and the data restrictions.

Required evidence and artifacts to retain

Keep artifacts that let an assessor reconstruct the decision and validate operation:

Governance artifacts

• Information Sharing Policy / Standard referencing AC-21. ¹
• Information Sharing Circumstances Register.
• Data restriction taxonomy and tagging guidance.

Operational artifacts

• Access requests (tickets/forms) identifying: partner, circumstance, datasets, requested actions. ¹
• Approval records showing the “match” decision and approver authority. ¹
• Provisioning evidence: IAM changes, role assignments, API keys issuance, tenant invitations.
• Logs showing enforcement or checks at time of sharing (workflow logs, policy engine decision logs, export logs). ¹
• Access review results and remediation actions.
• Exception records with scope and expiry. ¹

FedRAMP packaging note: structure artifacts so they cleanly map into your SSP narratives and ongoing evidence submissions; FedRAMP provides document templates that shape assessor expectations. ²

Common exam/audit questions and hangups

Expect these questions from a 3PAO or agency assessor:

• “Show me how an authorized user determines the partner’s authorizations match the data restrictions before sharing.” ¹
• “What are your defined information sharing circumstances? Who approves each?” ¹
• “How do you prevent a partner with ‘support’ access from downloading bulk exports?” ¹
• “Where is the evidence for the last sample of sharing events? Provide the request, approval, and the technical enforcement record.” ¹
• “What happens when restrictions change after access is granted?” ¹

Hangups that slow audits:

• Restrictions are described in prose but not mapped to entitlements.
• “Partner” is treated as a monolith, not a set of specific identities/roles.
• Sharing happens through multiple channels (UI export, API, support tooling) with inconsistent checks. ¹

Frequent implementation mistakes (and how to avoid them)

1. Mistake: Counting a contract clause as “authorization matching.”
   Fix: use contractual terms as inputs, but implement a real entitlement mapping and pre-share check with logs. ¹

2. Mistake: No defined sharing circumstances.
   Fix: publish a controlled list and force requests/technical paths to select one. If a path is not listed, treat it as prohibited until added. ¹

3. Mistake: Data restrictions are not machine-checkable.
   Fix: adopt tags and rule mappings, even if coarse at first, then refine. ¹

4. Mistake: Partners inherit broad internal roles.
   Fix: create partner-specific roles and limit to the minimum actions per circumstance; document why. ¹

5. Mistake: Missing evidence for “determination.”
   Fix: make the check produce an artifact by design (ticket fields, decision logs, export logs with policy decision ID). ¹

Enforcement context and risk implications

No public enforcement cases are provided in the supplied source catalog for AC-21, but the control is still high-stakes in FedRAMP because assessors test whether the control exists, is consistently applied across sharing channels, and is evidenced. Weaknesses typically manifest as audit findings such as inadequate access control enforcement, insufficient documentation, or inability to support sampling with records. These findings can delay authorization or drive continuous monitoring corrective actions. ¹

Practical 30/60/90-day execution plan

Day 0–30: Establish the share model and minimum viable checks

• Inventory sharing pathways (exports, APIs, support access, integrations) within the authorization boundary. ¹
• Define your initial “sharing circumstances” list and required approvers.
• Create a basic restriction taxonomy (start small: a handful of tags tied to clear allowed/prohibited actions).
• Add required fields to the access request workflow to capture: circumstance, data category/tag, partner identity, requested actions, expiry.
• Pilot the authorization matching check for the highest-risk pathway (often bulk export or support access). ¹

Day 31–60: Expand coverage and harden evidence

• Extend checks to remaining sharing pathways; remove “side doors” (ad hoc shares outside the workflow).
• Implement standardized partner role design and entitlement mapping to restrictions.
• Stand up an exception process with scope/expiry and post-event review.
• Run an internal sample-based test: pick recent shares and verify each has request, approval, provisioning, and enforcement logs. ¹

Day 61–90: Operationalize reviews and make it assessor-ready

• Launch periodic revalidation for partner access tied to your revocation triggers.
• Update SSP/control narrative and link artifacts to evidence locations; align packaging to FedRAMP documentation expectations. ²
• Train the approver set on what “match” means and what they must verify.
• Prepare an assessor walkthrough: one end-to-end sharing event with complete evidence and one exception case. ¹

Where Daydream fits (practitioner note): teams often lose time correlating access requests, approvals, and periodic reviews across systems. Daydream can centralize third-party access approvals, review cadences, revocation triggers, and evidence retention so AC-21 sampling is a retrieval task, not an archaeology exercise.

Frequently Asked Questions

Does AC-21 require a technical control, or can a process-only approach pass?

AC-21 requires a reliable way for authorized users to determine authorization match before sharing, and assessors need repeatable evidence of that determination. A process can work if it is mandatory, consistently used, and produces durable records; many teams still add technical enforcement to reduce drift. ¹

What counts as a “sharing partner” in a FedRAMP environment?

Treat any external party receiving access or data as a sharing partner: agencies, other tenants, subcontractors, integrators, and third parties performing support or operations. Scope the definition to sharing that occurs within or from the authorized boundary. ¹

How do we handle “view-only” sharing versus exports/downloads?

Model them as different sharing circumstances with different allowed actions and different restrictions. Then implement separate entitlements (roles/permissions) so “view-only” cannot silently become “export-capable.” ¹

We have multiple sharing channels (UI export, API, support tooling). Do we need the same check everywhere?

You need consistent ability to determine and enforce authorization match across all defined sharing circumstances. If different channels implement different checks, document the equivalence and keep evidence for each channel. ¹

What evidence is most persuasive to a 3PAO?

A sampled sharing event with a complete chain: request (with circumstance and restrictions), approval (explicit match decision), provisioning/change record, and logs showing the share occurred through the approved path. Exceptions should have the same chain plus compensating controls and closure evidence. ¹

How do we prevent access from lingering after a partner engagement ends?

Define revocation triggers tied to engagement/contract events and identity lifecycle changes, then run periodic revalidation that forces owners to confirm continued need and restriction alignment. Track removals as first-class evidence, not an afterthought. ¹

Footnotes

1. NIST Special Publication 800-53 Revision 5

2. FedRAMP documents and templates