SC-27 Platform-independent applications: requirements and evidence

What SC-27 platform-independent applications requires

An assessor or contract has asked for SC-27, and the first thing to know is that SC-27 is not in any SP 800-53B baseline. It applies only when your organization selects it through tailoring or an overlay, so the question is less "do we meet SC-27" and more "have we deliberately chosen it, and can we show why." The control asks the organization to define the platform-independent applications it relies on and to include them in its systems. In plain terms, a critical function should not depend on one operating system, browser or vendor platform, so that a compromise of that platform does not take the function down with it. The idea is familiar from disaster planning, but SC-27 is about security compromise rather than outage.

The difficulty is in the two decisions the control forces. First, you must scope which functions are critical enough to need a platform-independent path, which means working backward from mission or business functions, not from the technology inventory. Second, you must prove the choice. For each function you list, you need to be able to show the applications chosen, the platforms they run on, and the design documentation and configuration settings that make them work across those platforms. Release 5.2.0 gives SC-27 one organization-defined parameter and no control enhancements, so the parameter is where your decisions are recorded and where an assessor will look first. Confirm the current wording of that parameter in the OSCAL catalog before drafting it.

SC-27 also sits next to SC-29 (heterogeneity), the one related control the Release 5.2.0 catalog lists. Heterogeneity asks for diverse technologies so one exploited vulnerability cannot compromise every component, and SC-27 is one way to meet that intent at the application layer. Mapping the two together helps avoid duplicate evidence. Ask your assessor whether they expect SC-27 evidence on its own or as part of the SC-29 discussion, because the answer changes how you organize your design documentation and audit records.

Which systems and functions SC-27 applies to once selected

SC-27 is not in any SP 800-53B baseline, so it reaches a system only when the organization selects it through tailoring or an overlay. The cards below cover the decisions that determine whether it applies, what it should protect, and who must own those choices.

Selection through tailoring or overlay

Because SP 800-53B does not assign SC-27 to the low, moderate, high or privacy baseline, the control enters scope only when the organization's tailoring decisions or an applicable overlay select it. Record the selection, the rationale and the systems it covers in the system security plan. An assessor will look for that justification first, and a control that appears in no documented decision is treated as not selected.

Critical functions that must survive compromise

The control's purpose is continuity of critical functions when one platform is compromised. Start by listing the functions whose loss would breach a mission, safety or contractual obligation, such as authentication, logging, incident communications or a reporting duty. For each, decide whether a platform-independent application must perform it, and document the failure scenario it protects against.

Platform-independent application inventory

The control requires a defined list of platform-independent applications, so the inventory is the core evidence. Each entry should name the application, the critical function it supports, the platforms it runs on, and the system boundary it belongs to. Keep the list current when platforms are added or retired, since an assessor compares it against the system design documentation.

Ownership of application choices

Platform engineering usually proposes candidate applications, the security team reviews whether each one meets the defined function, and the system owner accepts the residual risk. Compliance records the decision and ties it to the SC-1 policy. Name these owners in writing, because the control's evidence is a decision trail, not a technical configuration alone.

Third-party and cloud-hosted platforms

When a critical function runs on a cloud or managed platform, the platform operator becomes part of the scope question. Confirm which components the organization controls, which it inherits from the provider, and whether the provider's shared responsibility documentation covers the function. Self-hosted open-source applications inside the organization's own accounts keep that boundary clearer, but the organization still owns the design decision.

Regulated and FedRAMP scope

FedRAMP's Rev5 baselines do not require SC-27 at Class B, C or D, so a FedRAMP authorization alone does not put it in scope. Organizations that select it for other reasons, such as a customer contract or an internal risk decision, should state that basis explicitly. Confirm with the authorizing official or contracting officer whether the selection is required or voluntary before planning evidence.

How an assessor tests SC-27

This table walks through the SP 800-53A Release 5.2.0 procedure for SC-27, which has one determination statement tested with examine, interview and test methods. Read each row as one artifact the assessor opens, the question they ask about it and the gap that most often causes a finding.

Assessment element	What the assessor asks for	Common finding
Determination statement	Whether the organization has included its defined platform-independent applications in the system, as SC-27 requires.	Organization cannot show that any application was chosen for cross-platform use, so the control appears unimplemented.
Examine: list of platform-independent applications	The organization-defined list, with each application named, its target platforms and the function it carries.	List is missing, out of date, or reads as a general statement with no named applications.
Examine: system design documentation	Architecture diagrams and design notes showing where each listed application sits and which critical functions it serves.	Design documents describe a different architecture from the running system, such as a retired host or an unlisted service.
Examine: system configuration settings and documentation	Deployed configuration for each application, including platform bindings, versions and how the application is kept on more than one platform.	Settings exist only on one host, or configuration documents are not tied to the version actually deployed.
Examine: system audit records	Logs or change records showing when applications were added, changed or removed, and who approved the change.	No audit trail of changes, so the assessor cannot confirm the list matches what runs in production.
Interview	Owners of the critical functions and platform engineers explain why each application runs cross-platform and how they would use it during a platform compromise.	Staff describe the intent but cannot point to the design or configuration that makes it true.
Test	The assessor may check that a listed application starts and performs its function on a platform other than its primary one, using the documented configuration.	Testing is not possible because the alternate platform was never built or the application depends on the primary platform's services.
Evidence owner	The organization owns the list, the design and the change record. An implementation partner may prepare these artifacts, but only the independent assessor reports on whether the control is met.	Responsibility for the list is unclear, so no one keeps it current after the initial assessment.

Implementing SC-27 in five steps

This sequence turns SC-27 from a sentence in a policy into a defined list of platform-independent applications, each tied to the critical functions it protects, with design documentation, verified configuration and audit records that an assessor can examine.

Define the parameter and critical functions
Start by deciding which applications count as platform-independent for your organization. SC-27 has one organization-defined parameter, so the organization must name the applications and the critical functions they are meant to cover. Involve the business owners of those functions, not only the platform team, because the list determines what survives a platform compromise. The output is a signed-off list of applications and functions, with an owner for each entry. Confirm the wording of the parameter with your assessor before you rely on it, since the assessor examines this list first.
Map each function to its carrying application
For every critical function, record which platform-independent application carries it, which platforms that application runs on, and what happens to the function if the primary platform is compromised. Gaps appear at this step: a function with no application, or one that depends on a single platform, needs a decision before design starts. The output is a traceability table linking functions, applications, platforms and owners. Keep the table under version control so changes are visible later.
Document the design and dependencies
Write the system design documentation that shows where each platform-independent application runs, how users and administrators reach it, and which shared dependencies it has, such as identity services, DNS, certificates and data stores. Shared dependencies are a common weak point: an application that runs on two platforms but depends on one identity provider does not survive that provider's compromise. The output is an architecture document that matches the mapping in the previous step and names the owner of each dependency.
Configure and verify the deployed systems
Deploy and configure the applications on the platforms named in the design, then verify the configuration against the documented design. Test each mapped function on its alternate platform, not only on the primary one, and record the results. Keep the configuration settings and their documentation with the test evidence. Where you use self-hosted open-source platforms in your own infrastructure, the implementation partner can prepare the configuration and test records, but the organization owns the result and the decision to accept it. The output is configuration evidence and test records for each function.
Set a review cycle with audit records
Define how often the list, the mapping and the design are reviewed, and what triggers an earlier review, such as a new platform, a retired application or a change to a critical function. Make sure the systems generate audit records for the platform-independent applications and that those records are retained and reviewed. Assessors will look for system audit records as evidence that the control operates over time, not only at go-live. The output is a documented review procedure, a review log and an audit record trail that an independent assessor can sample.

How the platform-independence decision shows up in audit evidence

The SC-27 decision becomes testable only when the organization can show a traceable path from each critical function to the platform-independent application that carries it. An assessor working from the SP 800-53A procedure for SC-27 will look for the list of platform-independent applications first, then ask how each entry maps to a function the organization has said must survive a platform compromise. Start with a register that names each critical function, the application chosen to perform it, the platforms that application runs on, and the owner who approved the choice. Each row should point to the system design documentation that explains why that application was selected, so the list and the architecture tell the same story.

Configuration evidence proves the list is more than a document. For each listed application, keep records of the deployed configuration showing the platforms it is installed and running on, along with the settings that govern that deployment. Exported configuration files, deployment manifests and inventory extracts from the self-hosted environment are the usual forms. The reader should confirm with their assessor which format they accept and whether the organization's own configuration management baseline already captures this information, since duplicating it in two places creates drift that an assessor will notice.

The list also needs a review trail. Audit records should show that someone reviewed the set of platform-independent applications at a defined frequency and after significant changes, such as a platform retirement or a new critical function. Those records should be retained with the rest of the audit log so an assessor can compare the list at two points in time. Plan for the case where a review finds that a function now depends on a single platform again. That finding should trigger a documented decision in the plan of action and milestones rather than a silent edit to the register.

Evidence that passes SC-27 and how to keep it current

SP 800-53A asks an assessor to examine four artifacts for SC-27: the list of platform-independent applications, system design documentation, configuration settings with their documentation, and system audit records. Each artifact goes stale in a different way, so each needs its own refresh trigger between assessments.

Approved platform-independent application list

This is the inventory that names each application the organization has defined as platform-independent, along with the platforms it must run on and the critical function it protects. Assessors compare the list against what is actually deployed. Confirm that the list matches the organization-defined parameter for SC-27, that each entry has an owner, and that retired applications are removed rather than left in place.

System design documentation

Design documents show how the platform-independent applications fit into the architecture, which platforms each one can run on, and how a failure on one platform leaves the critical function available on another. Update the design record whenever a platform is added, removed or retired, and whenever the hosting pattern changes, so the diagrams reflect what the system really does.

Configuration settings and related documentation

Configuration records show how each application is deployed on each platform, including versions, image or package sources, and the settings that keep the application functionally equivalent across targets. Store these under configuration management so every change produces a dated record. Check that the documented settings match the running configuration at the time of assessment.

System audit records

Audit records show deployments, failovers and platform switches, which is how an assessor confirms the applications actually run across platforms in operation. Review sample records for each listed application and confirm that events are time-stamped and retained long enough to cover the assessment period.

Change-triggered update rules

Set explicit triggers that force a refresh of the four artifacts: a new platform, a retired application, a changed hosting pattern, or a change to the organization-defined parameter. Route each trigger through the change control process so the list, design documents and configuration records are updated in the same change ticket rather than on a fixed calendar.

Ownership and review cadence

Name one owner for the SC-27 evidence set and one reviewer who is independent of the deployment team. The owner runs a review of all four artifacts before each assessment and after any trigger fires. Confirm with your assessor which review interval and sign-off records they expect, since the control text does not set them.

What meeting SC-27 costs in money and effort

This table breaks down the cost and effort components of meeting SC-27 and marks which ones are one-time and which recur. Use it to see who is paid for each component and which drivers you control when you request a quote. No prices are given because the supplied NIST sources do not estimate implementation costs.

Cost component	Who is paid or who spends effort	One-time or recurring	What drives it up or down
Defining the list of platform-independent applications	Internal architects and security staff, optionally an implementation partner for the written scope	One-time, revisited when the list changes	Number of critical functions in scope and how many already run on more than one platform
Design documentation and configuration baseline	Platform engineers, with partner time if the work is fixed-scope	One-time, then updated with each design change	Number of platforms each application must run on and how many configuration settings differ between them
Verification testing across platforms	Internal QA or a security testing provider	Initial testing is one-time, regression testing recurs	Count of platforms, release frequency and whether tests are automated
Audit record collection and retention	Operations staff, plus any log platform licensing already in place	Recurring	Log volume per platform and how long records must be kept
Evidence upkeep	Compliance lead or control owner	Recurring, tied to each assessment cycle	Frequency of configuration changes and how much evidence is generated automatically
Independent external review	Independent assessor or testing firm, paid by the organization	Recurring at each assessment cycle	Scope of the assessment, number of platforms examined and quality of prepared evidence
Assessor sampling and follow-up questions	Assessor fees, with internal staff time to answer requests	Recurring at each assessment cycle	Clarity of design documents and whether evidence is organized by application and platform
Software licensing for tooling	Organization, paid to commercial vendors, if proprietary tools are chosen	Recurring license fees	Choice of self-hosted open-source tooling can remove or reduce this line, but support and staffing costs remain
Ongoing support or retainer	Implementation partner, if a support retainer is agreed	Recurring, if chosen	Scope and frequency of upgrades, reviews and testing agreed in writing

Who does what for SC-27: your team, a partner and the auditor

Your organization owns SC-27 in full. The control requires that defined platform-independent applications be included in the system, so the decisions about which applications qualify, why they were chosen and what they are expected to keep running during a platform compromise belong to you. No partner or auditor can make those decisions on your behalf, and an assessor will expect to see your name against each one.

Defining the organization-defined parameter: SC-27 has one parameter in Release 5.2.0, so your team must state which applications count as platform-independent and which critical functions they support.
Owning the application list: Maintain the list in your system security documentation, with versions, owners and the platforms each application runs on.
Making the risk decision: Decide whether the chosen applications are sufficient for your threat model, and record any residual risk and who accepted it.
Approving design and changes: Review the design that places these applications, and approve changes when platforms, applications or dependencies change.

Confirm that a named owner in your organization can explain the list and the risk decision to an assessor without referring to the partner.

Where organizations fall short on SC-27

SC-27 is short, but assessors test it against concrete artifacts: a defined list of platform-independent applications, a mapping to critical functions, current design documentation and audit records. The gaps below are the ones that most often leave the control unevidenced, and each one has a closing action an organization can check before an assessment starts.

No defined list of applications

SC-27 requires the organization to define which applications are platform-independent, and the first assessment object is the list itself. Many programs have a general intent to run critical tools across platforms but never write down which applications qualify, so an assessor has nothing to test against. Close it by publishing a named, versioned list with an owner, the platforms each application runs on, and the date it was last approved.

Critical functions never mapped

The purpose of SC-27 is continuity when one platform is compromised, so the list of applications has to be tied to the functions that must survive. Organizations often list tools without asking which business or security functions depend on them, which leaves gaps where a single platform still carries a critical function alone. Close it by mapping each critical function to at least one application that runs on a different platform, and recording where that mapping is not possible.

Design documents out of date

Assessors check system design documentation to confirm that the chosen applications actually run on the platforms the organization claims. When architecture diagrams predate a migration, a new cloud region or a platform change, the documentation contradicts the configuration the assessor observes. Close it by tying design document reviews to every change that moves an application or platform, and comparing the diagrams against current configuration settings before testing begins.

Configuration drift from the design

Even accurate design documents fail when deployed systems drift from them. An application documented as running on two independent platforms may have been reconfigured onto one host, or its failover target may have been retired without anyone updating the record. Close it by collecting configuration settings from each platform on a schedule and flagging any application whose live deployment no longer matches the approved list.

No audit trail for platform choices

Assessors also examine system audit records to confirm the platform arrangement is monitored and changes are visible. Without logs that show when an application was deployed, moved or taken off a platform, the organization cannot prove the arrangement held over time. Close it by confirming that deployment, configuration and decommissioning events for listed applications are written to audit logs that the team retains and can retrieve.

Ownership split between teams

Platform choices usually sit between application owners, platform engineering and security, and each assumes another team tracks the result. The control then has no accountable owner, and the list is not reviewed when a platform is retired or a vendor changes. Close it by naming one owner for the SC-27 list, documenting who approves additions, and setting a review point tied to platform change requests.

SC-27 questions buyers ask before hiring help

Is SC-27 required by default under NIST SP 800-53?

No. SC-27 is not assigned to any SP 800-53B security or privacy baseline, so it applies only when your organization selects it through tailoring or an overlay. Appendix C of SP 800-53 Rev. 5 lists it as implemented by the system. In practice, check your authorizing body's baseline, any agency or contract requirement, and your own risk assessment. FedRAMP's Rev5 baselines also do not require SC-27 at Class B, C or D, so confirm the class that applies to your system before assuming it is in scope.

What drives the cost and effort of SC-27 work?

Cost depends mainly on how many platform-independent applications you define, how many platforms they must run on, and how much existing system design documentation and configuration evidence you already have. Each application needs to be identified, justified and documented, and the configuration must be shown to function on the platforms you name. One-time costs include the initial inventory, design work and documentation. Recurring costs include reviewing the list when platforms or applications change. Ask any partner to price these components separately in the written scope.

How long does SC-27 implementation take, and what does it depend on?

No duration is established for SC-27 in the supplied sources, so confirm timing with the partner against your own environment. The schedule usually depends on how many applications are in scope, how many platforms each must support, whether the platforms are already running, and how quickly your team can provide design documents and access for testing. Assessment evidence also has to exist before an assessor arrives, so plan time for producing audit records and configuration documentation.

Can our internal team implement SC-27 without an outside partner?

Yes, if your team already owns the system design, can inventory applications across platforms, and can produce configuration and audit evidence. SC-27 is a single base control with one organization-defined parameter and no enhancements, so the work is narrower than many SP 800-53 families. Outside help becomes useful when the platform inventory is unclear, when several self-hosted platforms must be tested on each target, or when no one on staff has time to document the result against the assessment procedure.

What should we ask a partner for in a fixed-scope SC-27 quote?

Ask for a written scope that names each platform-independent application, the platforms it must run on, the systems in the boundary, and the evidence to be delivered. Request a deliverables list that matches the assessment objects in SP 800-53A, such as the list of applications, system design documentation, configuration settings and audit records. Also ask what is excluded, who approves changes to scope, what happens if a platform is added later, and which items are one-time versus recurring. DeployOpen works from fixed, written scopes, and a quote follows from that scope.

What does the auditor do, and what does the implementation partner do for SC-27?

The organization owns its controls and decides whether SC-27 is selected. An implementation partner, such as DeployOpen, prepares systems, configurations and evidence so the control can be tested. Only an independent assessor, auditor or certification body evaluates the control and issues any report or certificate. The partner does not determine whether the control passes. Confirm with your assessor which SP 800-53A procedures they will run and which evidence they expect before the partner begins work.

How do self-hosted open-source platforms help produce SC-27 evidence?

Self-hosted platforms running inside your own cloud accounts, data centers or air-gapped networks let you control configuration and keep audit records within your boundary. Evidence for SC-27 typically includes the application list, design documentation, configuration files and audit logs showing the platforms in use. Confirm with each platform's maintainers which configuration keys, logging options and portability features are available, because capabilities vary by product and version and should not be assumed.

How DeployOpen prepares SC-27 evidence

DeployOpen scopes SC-27 in writing before any work starts. The written scope names which applications are defined as platform-independent, which platforms they must keep running on if one platform is compromised, and which critical functions must survive that failure. Because SC-27 has one organization-defined parameter in Release 5.2.0, that list is the decision the organization owns. DeployOpen can help draft the candidate list from the system's functions, but the organization should approve it, record the rationale in the system security and privacy plan, and confirm that the list matches what SP 800-53A expects an assessor to examine: a list of platform-independent applications, system design documentation, configuration settings and audit records.

DeployOpen builds and documents the chosen applications inside your own infrastructure. Work covers deploying each application on the separate platforms named in the scope, configuring them to the agreed settings, and proving they can run without depending on the failed platform. Typical artifacts include design diagrams showing where each function runs, configuration files kept under version control, and runbooks for failing over to the alternate platform. Recurring costs sit mostly in operating the second platform, keeping its versions aligned and retesting after changes. Ask any partner to state in the quote which of these items are one-time deliverables and which are retainer activities. SC-27 has no related control enhancements, so the assessment will focus on whether the defined list is implemented and documented, not on additional technical features.

DeployOpen does not issue audit reports, attestations or certifications. Independent assessors do. An assessor, or the agency or authorizing official relying on the assessment, will test the organization's claims against the evidence, and DeployOpen's role is to prepare systems, configurations and documentation so that evidence exists and is traceable. Before engaging a partner, confirm with the organization's assessor which evidence formats they accept, how audit records should show platform use, and whether the platform-independent list must be reviewed on a set schedule. Only the organization owns the control; the assessor decides whether it is met.

SC-27 Platform-independent applications