COSO Principle 15: The entity communicates with external parties regarding matters affecting the functioning of internal control

For SOC 2 teams, “internal control” is rarely contained inside your org chart. Customers push security requirements, auditors ask for clarification, regulators request information, and critical third parties notify you about outages or vulnerabilities. COSO Principle 15 is the control-system expectation that these external interactions are not ad hoc. They must be designed, repeatable, and traceable to internal control outcomes.

The fastest way to implement this principle is to treat external communication as a small set of governed workflows: who can commit the company externally, what topics require formal review, which events trigger notices, how inbound signals (complaints, incidents, audit inquiries) enter your control environment, and what evidence you keep to prove the loop closed.

This page is written for a Compliance Officer, CCO, or GRC lead who needs requirement-level guidance to stand up an auditable program quickly. It focuses on execution: stakeholder mapping, channel governance, escalation, recordkeeping, and audit-ready artifacts aligned to SOC 2’s Trust Services Criteria mapping to COSO. Source: AICPA 2017 Trust Services Criteria (revised points of focus 2022) [AICPA TSC 2017].

Regulatory text

Requirement (SOC 2 / Trust Services Criteria mapping to COSO): “COSO Principle 15: The entity communicates with external parties regarding matters affecting the functioning of internal control.” ¹

What the operator must do: You must be able to show that external communications relevant to internal control are (1) identified as required, (2) assigned to accountable owners, (3) executed through defined channels with appropriate review/approval, and (4) captured as evidence, including how the organization responded when external parties raised control-relevant issues. ¹

Plain-English interpretation (what auditors mean by “communicates with external parties”)

For SOC 2 purposes, this principle is about reliability and traceability:

• Outbound: You communicate control-relevant information to external parties in a controlled way (for example, incident notifications, security statements, commitments in contracts, responses to customer security questionnaires, regulatory inquiries, auditor confirmations).
• Inbound: You receive and process external information that should change your control operation (for example, customer complaints, vulnerability disclosures, third-party incident notices, audit requests, legal letters, hotline tips).

Auditors typically test whether these communications are governed (policy/procedure), complete for your scope (stakeholders and triggers identified), and evidenced (tickets, emails, portal exports, meeting minutes, approvals).

Who it applies to (entity and operational context)

This applies to service organizations pursuing or maintaining SOC 2 where external stakeholders influence or depend on controls. Typical in-scope contexts:

• B2B SaaS and cloud services: customer assurance, incident notifications, contract commitments, status communications.
• Financial services or regulated customers: higher volume of security/legal inquiries and procurement requirements.
• Organizations with material third parties: reliance on subservice organizations, critical software providers, data processors, and infrastructure providers.
• Organizations with independent auditors: SOC 2 exam fieldwork involves repeated external communications that must be controlled and retained.

Practically, if your controls rely on external inputs (third-party SOC reports, penetration test attestations, processor statements) or create external commitments (SLAs, DPAs, security addenda), you are in scope.

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

Below is a build sequence that maps cleanly to how auditors test TSC-aligned communication controls.

Step 1: Define “control-relevant external communications” for your scope

Create a short taxonomy that your teams can apply consistently:

• Assurance communications: SOC reports, bridge letters, audit PBC responses, control attestations.
• Security communications: incidents, vulnerabilities, pen test summaries (as shareable), security advisories.
• Privacy/data communications: data subject requests routed via customers, breach notices, subprocessors.
• Commercial/control commitments: contractual security obligations, SLAs, customer questionnaire responses.
• Third-party operational notices: outages, changes, deprecations, major configuration changes that affect control operation.

Deliverable: a one-page “External Communications in Scope for Internal Control” standard owned by Compliance.

Step 2: Stakeholder map with owners, channels, and objectives

Build a matrix that ties each external party type to an accountable internal owner and approved channel.

Example stakeholder matrix (minimum viable):

External party	Typical topics	Approved channels	Accountable owner	Control objective
Customers/prospects	Security questionnaires, incidents, contractual commitments	Ticketing + approved email templates + GRC repository	GRC / Security + Legal for commitments	Accuracy, consistency, approved commitments
Regulators/authorities (if applicable)	Requests, inquiries	Legal-managed mailbox + counsel workflow	Legal/Compliance	Timely, controlled responses
Independent auditor	PBC, clarifications, evidence requests	Auditor portal + GRC evidence store	GRC lead	Completeness and traceability
Critical third parties	Incident notices, changes	Vendor management inbox + ticketing	Third-party risk owner	Intake and escalation
General public / researchers	Vulnerability disclosures	Security intake form + bug bounty channel (if used)	Security	Proper intake, triage, response

Deliverable: stakeholder communication RACI and channel register.

Step 3: Establish triggers and SLAs for escalation (operational rules)

Define what events require formal external communication or intake handling. Keep it concrete:

• Outbound triggers: security incident meeting your notification criteria; significant control change; planned downtime; contractual updates requiring customer notice; auditor request deadlines.
• Inbound triggers: external complaint about security/privacy; third-party incident notice; vulnerability report; legal request.

For each trigger, set:

• Required internal reviewers (Security, Legal, Privacy, Comms).
• Who can approve external statements.
• Where the record is stored.
• How you confirm closure (customer notified, regulator response sent, remediation ticket created).

Deliverable: “External Communication Triggers & Escalation Procedure” with approval authority.

Step 4: Standardize content with templates and guardrails

Create templates that reduce inconsistent statements:

• Incident notification template (facts, scope, customer impact, next update cadence).
• Security questionnaire response guidelines (what must be sourced from approved control descriptions).
• Audit response template (links to evidence, control narrative, exceptions statement).
• Third-party intake acknowledgement (what you commit to, what you don’t).

Guardrails to include:

• Prohibit unapproved security claims (for example, “we are compliant with X”) unless reviewed by Compliance/Legal.
• Require references to the current control narrative and system description where relevant.

Deliverable: template pack with version control.

Step 5: Evidence and retention design (make it auditable)

Auditors will ask, “Show me.” Design evidence capture as part of the workflow:

• Route communications through systems that log activity (ticketing, auditor portals, CRM notes, GRC tool).
• Require attachments or links to outbound messages and inbound requests.
• Tag items as “SOC2-control-relevant external comms” for retrieval.

A practical pattern: create a single “External Comms Evidence” folder structure (or Daydream control) with subfolders by stakeholder type and month, and require each comms item to have a corresponding ticket ID.

Deliverable: evidence map and retention rules aligned to your recordkeeping policy.

Step 6: Test operating effectiveness monthly (lightweight)

Run a monthly spot-check:

• Pick samples across categories (customer questionnaire, third-party incident notice, auditor request).
• Confirm approvals happened.
• Confirm the record includes the message and resulting action (ticket, risk acceptance, remediation).

Deliverable: monthly QA checklist and results log.

Required evidence and artifacts to retain

Keep artifacts that prove both communication and control response:

1. Policy/standard
   • External communications standard covering scope, roles, channels, approval authority.
2. Procedures
   • Triggers and escalation playbooks (incident comms, third-party notices, regulatory inquiries).
3. Records of outbound communications
   • Copies of customer notices, auditor responses, questionnaire submissions, contract security addenda redlines or approval notes.
4. Records of inbound communications
   • Intake tickets for complaints/vulnerability disclosures, third-party incident notices, regulator inquiries.
5. Approvals
   • Evidence of Security/Legal/Compliance review for sensitive statements (email approvals, ticket approvals, workflow approvals).
6. Closure evidence
   • Remediation tickets, risk register updates, post-incident reports, customer follow-up records.
7. Periodic QA
   • Sampling logs, findings, corrective actions.

If you use Daydream, map these directly to the control record and attach evidence to each operating period so audit requests become retrieval tasks, not archaeology.

Common exam/audit questions and hangups (what to be ready for)

Auditors commonly probe these areas for this requirement:

• “Which external parties matter for internal control in your system?” If you can’t articulate your stakeholder map, the control looks informal.
• “Who is authorized to communicate externally about incidents or security posture?” Auditors look for approval authority and evidence it was followed.
• “Show me an example where external input changed your controls.” You need at least one traceable case: third-party notice → risk assessment → remediation.
• “How do you ensure customer questionnaire answers are consistent and accurate?” Expect requests for templates, source-of-truth control narratives, and review steps.
• “Where is the evidence stored, and how do you retrieve it?” Searchability is a control attribute.

Frequent implementation mistakes (and how to avoid them)

1. Mistake: Treating external comms as purely a PR function.
   Fix: Make Compliance/Security co-owners for control-relevant topics, with documented approval gates.

2. Mistake: No boundary between “support emails” and “control-relevant communications.”
   Fix: Add a tagging rule and escalation triggers so support can route issues into formal workflows.

3. Mistake: Questionnaires answered from memory.
   Fix: Require answers to cite the current control narrative, policies, or system configurations, then retain that linkage as evidence.

4. Mistake: Evidence exists, but it’s scattered.
   Fix: Define one system of record (or a documented evidence index) and enforce it through process, not reminders.

5. Mistake: Third-party incident notices stop at the inbox.
   Fix: Mandatory intake ticket + severity triage + documented decision (monitor, remediate, or accept risk).

Enforcement context and risk implications (what’s at stake)

No public enforcement cases were provided in the source catalog for this requirement, so this section focuses on practical risk. Weak external communications create measurable exposure:

• SOC 2 report risk: auditors may report exceptions if you cannot evidence that communications are controlled and complete.
• Contractual risk: inconsistent or unauthorized commitments in external statements can create obligations you cannot meet.
• Incident risk: poor outbound notification control increases the chance of inaccurate statements; poor inbound intake increases the chance you miss a material signal (for example, third-party compromise notice).

Practical 30/60/90-day execution plan

Days 0–30: Stand up the minimum auditable control

• Draft and approve the external communications standard (scope, roles, channels, approvals).
• Build the stakeholder matrix and RACI; get sign-off from Security, Legal, Support, and Sales Ops.
• Create templates for incident notices, questionnaire responses, and auditor communications.
• Define evidence storage and naming conventions; align to your retention policy.

Deliverables: standard + matrix + templates + evidence map.

Days 31–60: Operationalize workflows and capture evidence

• Implement intake routing: dedicated mailboxes/forms feed ticketing with required fields.
• Implement approval workflows for sensitive external statements.
• Train front-line teams (Support, Sales Engineering, Customer Success) on triggers and routing.
• Start tagging and storing evidence in your system of record (or Daydream control attachments).

Deliverables: workflow configs + training records + first month of evidence.

Days 61–90: Prove operating effectiveness and close gaps

• Run monthly sampling and document results.
• Fix breakdowns: missing approvals, missing attachments, unclear ownership.
• Add coverage for any missed stakeholder category (common miss: critical third parties and vulnerability reporters).
• Prepare an “audit-ready” evidence index for the period.

Deliverables: QA log + corrective actions + audit evidence index.

Frequently Asked Questions

Do we need to notify customers for every incident to meet COSO Principle 15?

No. You need defined criteria for when external notification is required and evidence that you followed it. Auditors focus on whether your decision process is documented, approved, and repeatable ¹.

Does external communication include third-party (vendor) management?

Yes, when third parties can affect your control environment. You should capture third-party notices, SLAs, and security communications as inbound signals and show how you assessed and responded ¹.

What evidence is “enough” for questionnaire responses?

Keep the customer request, your submitted response, and proof of review/approval for sensitive claims. If answers rely on policies or control narratives, keep links or attachments that show what source you used ¹.

Our Sales team emails security statements directly. How do we control that without slowing deals?

Provide pre-approved language blocks and a fast approval path for exceptions. Put a rule in writing: only approved templates can be sent without Compliance review, and store the final response in your evidence repository.

Can Slack messages count as evidence for external communications governance?

Slack can support evidence of internal approvals, but you still need a durable record of what was sent externally and when. If Slack is part of the approval chain, export or link the approval record to the ticket or GRC evidence item.

How does Daydream help with this requirement in practice?

Daydream can act as the control record and evidence hub: you define the communication control once, then attach recurring artifacts (samples, approvals, outbound messages, intake tickets) by period. That reduces audit scramble because retrieval becomes a structured workflow.

Related compliance topics

• 2025 SEC Marketing Rule Examination Focus Areas
• Access and identity controls
• Access Control (AC)
• Access control and identity discipline
• Access control management

Footnotes

1. AICPA TSC 2017