AC-25 Reference Monitor. Implement a reference monitor for [organization-defined] that is tamperproof, always invoked, and small enough to be subject to analysis and testing, the completeness of which can be assured
Reference Monitor. Implement a reference monitor for [organization-defined] that is tamperproof, always invoked, and small enough to be subject to analysis and testing, the completeness of which can be assured.
5
artefacts
0
held by a system
2
at each review
hard
to go live
Policy repository / GRC workspace
where the evidence lives
teal = a system already holds it · olive = produced at each review
system holds itEvidence a system already holds
none for this control
periodic reviewEvidence produced at each review
- Tamper protection evidence for the monitor itself, such as memory protection or signed and immutable deployment · Identity provider / directory
- Analysis or test results showing the monitor is small enough for its completeness to be assured · Identity provider / directory
governing documentDocuments that govern the control
- Identification of the access control policies the reference monitor mediates · Policy repository / GRC workspace
- Design documentation demonstrating the monitor is always invoked, with no bypass path around it · Policy repository / GRC workspace
- Verification that the monitor cannot be disabled or reconfigured by the subjects it mediates · Policy repository / GRC workspace
First move
This control is evidenced by people and documents, not systems. Put the document under version control with an owner and review date, and log each review as a record with reviewer and date. Do not try to automate it.
Common gaps auditors find
- A bypass path exists for maintenance or break glass access that the always invoked claim does not cover
- Tamperproof asserted from platform hardening with no evidence specific to the monitor
- Size and complexity never analysed, so completeness of mediation is claimed rather than assured
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 sheetAC-24 Access Control Decisions. [organization-defined] to ensure [organization-defined] are applied to each access request prior to access enforcement · AT-1 Policy and procedures for awareness and training