8.17 Clock synchronization
The clocks of the organization's information processing systems are to be kept in step with approved time sources. Purpose: allow security events and other recorded data to be correlated and analysed, and support incident investigations. Guidance: document and implement external and internal requirements for how time is represented, how reliably it is synchronized and how accurate it must be, which may come from law, regulation, contracts, standards or internal monitoring. Define one standard reference time for the organization and apply it to all systems, including building management, entry and exit and other systems that may help investigations. Use a reference clock for logging systems tied to a national atomic clock radio broadcast or GPS, giving a consistent, trusted source for accurate timestamps, and keep networked systems aligned with it through protocols such as NTP or PTP. Two external time sources can be used together to improve reliability, with any difference between them managed. Where several cloud services, or cloud and on-premises services, are combined, synchronization is harder, so monitor each service's clock and record the difference to limit the risk of discrepancies. Other information: correct clocks keep event logs accurate, which matters for investigations and for evidence in legal or disciplinary cases; wrong timestamps hamper investigations and weaken evidence.
Source: ISO/IEC 27002:2022, 8.17. The statement above is our statement of the clause, read from the published text and cited so you can check it against the official text, not the instrument verbatim. Open ISO/IEC 27002:2022 in the compliance library.
ISO/IEC 27002 is guidance on the Annex A controls; certification is against ISO/IEC 27001. Use this set when your sheet follows the 27002 numbering.
These are the artefacts auditors commonly ask for on this requirement, our guidance rather than text from the standard. Your assessor decides what is sufficient in your context, and asks for samples across the period when a report covers one.
system holds itEvidence a system already holds
- NTP or PTP configuration showing systems synchronized to the approved reference clocks, including building management and physical access systems · Physical access / facilities
periodic reviewEvidence produced at each review
- Evidence of a trusted reference source such as GPS or national time service, and use of two external sources where adopted · Document repository
- Records of time offsets for cloud services where direct synchronization is not possible · Cloud console / configuration management
governing documentDocuments that govern the control
- Documented time requirements (representation, accuracy, synchronization) and the defined organizational reference time · Document repository
- Monitoring of clock drift across systems, with alerts on deviation · Policy repository / GRC workspace
First move
Common gaps auditors find
- Physical access and CCTV systems run on unsynchronized clocks, breaking correlation with IT logs
- Systems synchronize to arbitrary internet time servers not approved by the organization
- Time zones are mixed across logs without a standard representation
- Clock drift is not monitored, so failures of the time service go unnoticed
Do this for your whole sheet
Paste the rows you run your controls from and get this mapping for every control at once, with the periodic-review ones flagged and a first move per row. No account for the first run.
Build my evidence sheet8.16 Monitoring activities · 8.18 Use of privileged utility programs