Auditing ISO 27001 Annex A 8.12 Data Leakage Prevention is the technical verification of organisational safeguards against unauthorised information exfiltration. The Primary Implementation Requirement is the deployment of technical blocking and monitoring across endpoints and gateways, providing the Business Benefit of robust intellectual property protection and sustained regulatory compliance.
ISO 27001 Annex A 8.12 Data Leakage Prevention Audit Checklist
This technical verification tool is designed for lead auditors to establish the efficacy of technical controls preventing unauthorised data exfiltration. Use this checklist to validate compliance with ISO 27001 Annex A 8.12.
1. DLP Policy and Scope Formalisation Verified
Verification Criteria: A documented policy exists defining data classification categories and the specific technical rules for monitoring and blocking sensitive data transfers.
Required Evidence: Approved “Data Leakage Prevention Policy” or “Information Classification and Handling Standard” citing specific technical DLP triggers.
Pass/Fail Test: If the organisation cannot produce a formal document specifying the technical scope and rules for data leakage monitoring, mark as Non-Compliant.
2. Endpoint Data Exfiltration Controls Confirmed
Verification Criteria: Technical agents are active on all user endpoints to monitor and block unauthorised data transfers to USB, Bluetooth, or local printers.
Required Evidence: Endpoint DLP management console report showing “Active” status and “Block” rules for unmanaged removable media.
Pass/Fail Test: If a standard user can successfully copy a “Confidential” tagged file to an unencrypted personal USB drive without a system block or alert, mark as Non-Compliant.
3. Network Gateway Egress Filtering Validated
Verification Criteria: Network-level DLP controls are active at the perimeter to inspect outbound traffic (SMTP, HTTP/S, FTP) for sensitive data patterns.
Required Evidence: Configuration logs from the Web Proxy or Next-Gen Firewall (NGFW) showing active SSL inspection and DLP regex pattern matching.
Pass/Fail Test: If sensitive data (e.g. credit card numbers or PII) can be uploaded to a personal cloud storage site in plain text without detection, mark as Non-Compliant.
4. Email Content and Attachment Scanning Verified
Verification Criteria: Outbound email traffic is automatically scanned for sensitive keywords, metadata, or attachments that violate the classification policy.
Required Evidence: Email Security Gateway (e.g. Mimecast, Proofpoint) logs showing “Quarantined” or “Encrypted” events based on DLP rule triggers.
Pass/Fail Test: If an email containing a list of 100+ customer records can be sent to an external personal address without being blocked or automatically encrypted, mark as Non-Compliant.
5. Cloud Service (CASB) Integration Confirmed
Verification Criteria: Data Leakage Prevention extends to SaaS and Cloud environments (e.g. O365, G-Suite, Slack) via a Cloud Access Security Broker or native DLP tools.
Required Evidence: CASB dashboard or Microsoft Purview logs showing monitoring of “Public Link Sharing” and “External Guest” data access.
Pass/Fail Test: If sensitive files stored in corporate cloud drives can be shared via “Public Link” to any internet user without administrative oversight, mark as Non-Compliant.
6. Sensitive Data Pattern (Regex) Accuracy Verified
Verification Criteria: DLP rules utilise specific patterns, such as Regular Expressions (Regex) or Fingerprinting, to identify PII, Financial Data, or Intellectual Property.
Required Evidence: Review of the “DLP Rule Library” showing specific identifiers for National Insurance numbers, Credit Card PANs, or proprietary project codes.
Pass/Fail Test: If DLP rules are only based on generic “file extensions” rather than actual data content or metadata tags, mark as Non-Compliant.
7. DLP Incident Alerting and Triage Workflow Validated
Verification Criteria: Technical DLP breaches trigger automated alerts to the Security Operations Centre (SOC) or IT team for immediate investigation.
Required Evidence: Cross-reference of a “Blocked Transfer” event in the DLP console with a corresponding ticket in the Incident Management system.
Pass/Fail Test: If DLP events are logged locally but do not notify a responder for more than 24 hours, mark as Non-Compliant.
8. SSL/TLS Inspection Capability Confirmed
Verification Criteria: The organisation possesses the technical capability to decrypt and inspect encrypted outbound traffic (HTTPS) to prevent data hiding.
Required Evidence: SSL Inspection certificates installed on endpoints and “Decrypted Traffic” logs within the network security appliance.
Pass/Fail Test: If DLP monitoring is bypassed simply by using a website with HTTPS (which covers 99% of the web), mark as Non-Compliant.
9. Administrative Override and Justification Logs Verified
Verification Criteria: Where “Allow with Justification” rules exist, the organisation captures and reviews the business reason provided by the user for the transfer.
Required Evidence: DLP “Justification Report” showing user-entered comments and subsequent management review of those overrides.
Pass/Fail Test: If users can override DLP blocks without providing a recorded reason or if those reasons are never reviewed by a supervisor, mark as Non-Compliant.
10. Periodic DLP Rule Effectiveness Review Recorded
Verification Criteria: Management or Security teams perform regular “False Positive” and “False Negative” tuning to ensure DLP rules remain effective.
Required Evidence: Quarterly DLP Performance Reports or minutes from Security Committee meetings reviewing DLP efficacy.
Pass/Fail Test: If the DLP configuration has not been reviewed or updated to reflect new data types or business processes in the last 12 months, mark as Non-Compliant.
| Control Requirement | The ‘Checkbox Compliance’ Trap | The Reality Check |
|---|---|---|
| Technical Blocking | Tool records “Policy.pdf” as ‘Uploaded’ and marks green. | Verify Enforcement. A policy is words; a “Pass” requires a technical block log from an endpoint or gateway. |
| Scope Coverage | SaaS tool identifies “DLP: Active” via a single API. | Check the Blind Spots. Does the DLP cover personal webmail and Chat apps, or just corporate email? |
| Encryption Bypass | Platform assumes HTTPS traffic is being monitored. | Verify SSL Inspection. If the firewall isn’t decrypting HTTPS, the DLP is blind to 90% of data leaks. |
| Pattern Matching | Tool logs that “Data is Classified”. | Verify the Regex. If the system can’t tell the difference between a phone number and a credit card, the control is weak. |
| Removable Media | Tool checks if “USB usage is discouraged”. | Perform a Live Test. If the GRC tool says “Compliant” but a USB stick works, the GRC status is a lie. |
| Cloud Leaks | Platform identifies “Cloud Storage Secure”. | Check Public Links. Real auditors demand a report of all “Public” or “Anyone with link” shares currently active. |
| Incident Loop | Tool reports “Zero DLP Incidents” as a success. | Check for False Negatives. Zero incidents often means the monitoring is broken, not that the data is safe. |
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