What evidence do auditors commonly ask for on SC-3 Security Function Isolation?

System and communications protection policy; Procedures addressing security function isolation; List of security functions to be isolated from non-security functions; System design documentation; System configuration settings and associated documentation; System audit records.

What is the most common gap auditors find on SC-3?

Security functions share execution domains with nonsecurity functions, with no isolation boundary between them

NIST SP 800-53 Rev 5 · SC - System and Communications Protection

`SC-3` Security Function Isolation

Isolate security functions from nonsecurity functions.

Source: NIST SP 800-53 Rev 5, SC-3. 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 NIST SP 800-53 Rev 5 in the compliance library.

Base controls and their enhancements. Which apply follows the baseline you are assessed against (for example FedRAMP Moderate or High, or the low, moderate and high baselines of SP 800-53B). Text in square brackets is a parameter your organisation sets.

artefacts

held by a system

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. To go live: easy when half or more of the artefacts are already held by a system, moderate from a quarter to a half, hard below a quarter.

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

none for this control

periodic reviewEvidence produced at each review

System audit records · Policy repository / GRC workspace
Test of Separation of security functions from non-security functions within the system · Document repository

governing documentDocuments that govern the control

System and communications protection policy · Policy repository / GRC workspace
Procedures addressing security function isolation · Policy repository / GRC workspace
List of security functions to be isolated from non-security functions · Document repository
System design documentation · Document repository
System configuration settings and associated documentation · Policy repository / GRC workspace
System security plan · Policy repository / GRC workspace

First move

No system holds this evidence for you: it is people and documents. Reminders and routing to the owner still save time. Put the document under version control with an owner and review date, and log each review as a record with reviewer and date.

Common gaps auditors find

Security functions share execution domains with nonsecurity functions, with no isolation boundary between them
No hardware or software separation mechanism is documented for isolating security functions from other code

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 sheet

SC-2(2) Separation of System and User Functionality | Disassociability · SC-3(1) Security Function Isolation | Hardware Separation