SOC 2 Evidence Library Template

What is a SOC 2 Evidence Library?

A SOC 2 evidence library organizes artifacts that demonstrate control effectiveness across the Trust Services Criteria: Security, Availability, Processing Integrity, Confidentiality, and Privacy. Auditors use this library to validate that controls operate as designed, not just that policies exist.

Why Auditors Need an Evidence Library

SOC 2 auditors require evidence that proves controls work in practice—logs, configurations, test results, and reports with timestamps and ownership. An organized library streamlines audits by providing direct access to artifacts, reducing clarification requests and accelerating Type II readiness.

Evidence Categories by Trust Services Criteria

Security (CC1-CC9)

• Access Controls (CC6): MFA configurations, access review logs, privileged user matrices
• Change Management (CC8): Change request approvals, testing records, rollback procedures
• Risk Management (CC3): Risk assessments, mitigation plans, monitoring reports
• Logical/Physical Access (CC6): Door access logs, server room controls, VPN configurations
• System Operations (CC7): Vulnerability scans, patch management, incident tickets
• Encryption (CC6): Key management procedures, certificate chains, storage audit logs

Availability (A1.1-A1.3)

• Infrastructure Resilience: Redundancy configurations, failover tests, uptime monitoring
• Backup & Recovery: Backup schedules, restore validations, RTO/RPO documentation
• Capacity Management: Resource utilization reports, scaling procedures, performance baselines

Processing Integrity (PI1.1-PI1.3)

• Data Accuracy: Validation controls, error handling logs, reconciliation procedures
• Processing Controls: Batch processing logs, transaction integrity checks, audit trails
• Quality Assurance: Testing protocols, defect tracking, release management

Confidentiality (C1.1-C1.2)

• Data Classification: Classification policies, labeling procedures, access restrictions
• Encryption & Masking: Encryption implementations, data masking logs, key rotations
• Secure Transmission: TLS configurations, secure channel validations, interception tests

Privacy (P1.1-P1.4)

• Notice & Choice: Privacy policy acknowledgments, consent records, opt-out logs
• Collection & Use: Data collection procedures, usage tracking, purpose limitations
• Retention & Disposal: Retention schedules, disposal certificates, anonymization processes
• Access & Accuracy: Subject access request logs, data correction procedures, audit trails

Ownership and Refresh Cadence

Assign evidence ownership to specific roles and establish refresh schedules based on control criticality and auditor expectations. Most evidence requires annual updates for Type II audits, but high-risk controls need quarterly validation.

Bridge Letters for Automation Tools

Automation tools (Vanta, Secureframe, Drata) generate reports but auditors often require bridge letters explaining what tools check versus what humans validate. Bridge letters map tool outputs to SOC 2 criteria and identify manual evidence for gaps.

Bridge Letter Template

[Your Organization Letterhead]

[Date]

[Auditor Name/Title]
[Audit Firm]
[Address]

Re: Bridge Letter for SOC 2 Trust Services Criteria - [Criteria, e.g., Security]

Dear [Auditor Name],

This letter bridges our automated compliance monitoring to SOC 2 requirements for [specific criteria]. Our [tool name] platform continuously validates [list controls, e.g., MFA enforcement, access reviews, vulnerability scanning].

What the tool validates:

• [Control 1]: [Description, e.g., Daily checks of Okta MFA configuration against user accounts]
• [Control 2]: [Description, e.g., Weekly scans for unpatched systems with automated alerts]

Manual validations and evidence:

• [Gap 1]: [Explanation, e.g., Tool does not validate access review effectiveness; we conduct quarterly manual reviews documented in [evidence artifact]]
• [Gap 2]: [Explanation, e.g., Tool monitors configurations but not incident response execution; we perform annual tabletop exercises with records in [evidence artifact]]

All evidence artifacts are maintained in our SOC 2 evidence library with ownership assignments and refresh cadences. We attest that controls operate as designed and provide additional documentation upon request.

Sincerely,
[Your Name]
[Title]
[Organization]

Template Structure for Your Evidence Library

Use this table structure to organize your library. Maintain in a shared drive or compliance platform with version control.

How to Implement This Template

Step 1: Map Your Controls
List all implemented controls by Trust Services Criteria. Reference SOC 2 guidance for complete mappings.

Step 2: Assign Ownership
Designate responsible parties for each evidence type. Include backups for continuity.

Step 3: Set Refresh Schedules
Base cadences on control risk and auditor requirements. High-impact controls refresh quarterly.

Step 4: Generate Initial Evidence
Collect current artifacts. Create missing ones through testing or exports.

Step 5: Validate and Audit
Review evidence quarterly. Prepare for external audits with mock walkthroughs.

Step 6: Maintain Continuously
Update library after changes. Use automation for low-risk controls, manual for complex ones.

Common Evidence Gaps

Organizations often lack:

• Change management evidence: Approvals and testing records for all changes
• Incident response validations: Tabletop exercises or real incident handling proof
• Privacy control artifacts: Consent logs and data subject access records
• Availability testing: Uptime reports and failover validations
• Processing integrity logs: Error handling and reconciliation procedures

Next Steps

Need help building your evidence library? Bell Tower engineers SOC 2 readiness assessments, evidence packages, and auditor handoff materials.

• SOC 2 Readiness Assessment
• Vendor Review Evidence Checklist
• Microsoft SSPA Reassessment Guide

Frequently Asked Questions

How often should I update the evidence library?
Refresh high-risk evidence quarterly, medium-risk annually. Conduct full library reviews before audits. Automation tools can handle daily checks for continuous controls.

Can automation tools replace manual evidence?
No. Tools validate configurations but not effectiveness. Use bridge letters to connect tool outputs to manual validations like access reviews or incident tests.

What if I don’t have all evidence yet?
Start with what you have and implement missing controls. SOC 2 allows for remediation plans. Auditors accept commitments to generate evidence during the audit period.

How do I organize evidence for auditors?
Use clear folder structures by criteria (e.g., /Security/CC6/Access_Controls/). Include metadata files with ownership, dates, and validation status. Provide index documents for navigation.

Do I need external help for SOC 2 evidence?
Many organizations manage internally with templates. However, complex environments benefit from advisors who accelerate readiness and ensure auditor acceptance.