Developer Screening SA-21

Source: NIST SP 800-53 Rev.5, System and Services Acquisition family NIST SP 800-53 Rev.5. The baseline shows the lowest SP 800-53B baseline (Low / Moderate / High) this control appears in NIST SP 800-53B.

Control guide — plain-English, per NIST SP 800-53

SA-21 (Developer Screening) requires that the people who build your system — its software, components, and services — are vetted to a trust level that matches the people who run it. It targets outside or contract developers; screening your own employees falls under PS-3 (Personnel Screening). You define two things: the access authorizations a developer needs to do the work, and the extra screening criteria — background checks, citizenship, clearances — they must satisfy first. It is a System and Services Acquisition control that appears at the High baseline, for systems where a compromised developer would do real damage.

What good looks like

• Know who builds it — name the outside developers, contractors, and suppliers who write or assemble the code and components that run on the server.
• Define the access a developer role actually needs, and the screening criteria they must pass (for example, a criminal background check and confirmed identity) before they touch the system.
• Put it in writing — make screening a clause in the contract or agreement, not a verbal understanding.
• Verify and record that each developer was screened before access was granted, with the date.
• Re-check on a schedule and when a developer’s role changes or the vendor’s ownership changes — company ownership can affect reliability and trust.

Framework mapping

• NIST CSF 2.0 — GV.RR-04 — Cybersecurity is included in human resources practices

How to move it toward Implemented

• Write a one-page developer screening requirement: which parts of the system it covers, the access level a developer receives, and the exact screening each must pass (for example, a background check and identity verification).
• Add that requirement as a clause in every contract, statement of work, or agreement with an outside developer or vendor — and require it to be met before work or access begins.
• Collect the evidence that each current developer was actually screened — a signed attestation from the vendor, or a completed background-check record — and file it with the date, saved as a dated file.
• Set a review date to re-confirm screening on a schedule, and to re-check whenever a developer’s role or the vendor’s ownership changes.
• Attach the signed screening requirement and the developer screening records as hardening evidence on the asset, naming SA-21 in the Requirement field — that moves it from ‘To assess’ toward ‘Completed’.