A.8.17 Clock synchronization
The clocks of the organization's information processing systems are to be kept in step with approved time sources. Purpose (stated in ISO/IEC 27002:2022): enables correlation and analysis of security events and recorded data and supports incident investigations. As an Annex A reference control, it is compared with the controls determined in risk treatment (6.1.3 c) and recorded in the Statement of Applicability as included or excluded, with the justification and implementation status (6.1.3 d); implementation guidance is ISO/IEC 27002:2022 8.17.
Source: ISO/IEC 27001:2022, A.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 27001:2022 in the compliance library.
Clauses 4 to 10 are the management-system requirements: none of them can be excluded when an organisation claims conformity. The 93 Annex A controls are a reference set: one may be excluded with a justification in the Statement of Applicability. Certification bodies assess conformity; the evidence lists here are what auditors commonly ask for, not a list the standard prescribes.
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
governing documentDocuments that govern the control
- Statement of Applicability entry for control A.8.17, showing inclusion or justified exclusion, implementation status and the risks it treats · Policy repository / GRC workspace
- 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 sheetA.8.16 Monitoring activities · A.8.18 Use of privileged utility programs