SC-4 Information in shared system resources

What SC-4 requires when one process hands memory to another

SC-4 requires the system to prevent unauthorized and unintended transfer of information through shared system resources. For a compliance lead or engineer facing this control at a moderate or high baseline, or at a FedRAMP Class C or D system, the practical question is simple: when one user or process releases memory, storage or registers, can the next user or process read what was left behind? The risk is residual data. A process may write session tokens, decrypted records or key material into RAM, a swap file, a temporary disk block or a CPU register. If the platform hands that space to another tenant or process without clearing it, the earlier data can surface. SP 800-53B assigns SC-4 to the moderate and high baselines, and Appendix C of SP 800-53 marks it as a control implemented by the system rather than by the organization's policy alone.

The control is hard to own because the protection usually sits below the application. Object reuse is typically enforced by the operating system kernel, the hypervisor, the container runtime, the hardware platform and the storage layer, often through a cloud provider's managed service. Your team may run the workload, but it may not control how memory pages are zeroed or how deleted volumes are scrubbed. Assign a named owner for each layer, and record which layer provides the protection and what evidence it produces. Confirm with each vendor or provider in writing how object reuse is handled, which configuration settings govern it, and what documentation they will supply. Where a layer is inherited from a managed service, the inheritance must be stated in your system security plan and backed by the provider's own evidence, not assumed.

Which systems and layers fall inside SC-4 scope

SC-4 applies wherever shared resources carry information between users or processes, so scope starts with which systems your baseline selects and which layers you run yourselves. The cards below cover the decisions that change who owns the work and what evidence an assessor will ask for.

Moderate and high impact systems

SP 800-53B assigns SC-4 to the moderate and high baselines, so a system categorized at moderate or high impact brings the control into scope. Low-impact systems do not select it. Confirm the categorization in your system security plan, because a change in impact level changes whether SC-4 must be implemented and assessed. Check that every component in the boundary inherits the same categorization.

FedRAMP Rev5 Classes C and D

FedRAMP's Rev5 baselines require SC-4 at Classes C and D, so cloud services seeking those authorizations must show residual information protection for their shared infrastructure. Ask your sponsoring agency or authorization team which class applies, since the class sets the evidence depth. Cloud providers and their hosting layers may carry much of this, so confirm which parts your package inherits and which you must document yourselves.

Memory, swap and temporary files

Object reuse risk sits in RAM, swap space, temporary directories and scratch files that a process writes and another process later reads. Map each of these to the operating system that manages them and document how freed pages and deleted blocks are cleared before reallocation. Include swap encryption and tmpfs settings in the review, because they determine whether residual data can persist across process boundaries.

Block storage and backups

Block volumes, snapshots and backup repositories hold data that outlives the process that wrote it. When a volume is reassigned or a snapshot restored, residual blocks from a previous tenant or workload may be exposed. Ask who performs zeroing or cryptographic erase, whether the platform does it on deallocation, and what record proves it. This is the layer where operators most often assume inheritance without checking.

Container and VM hosts

The organization owns SC-4 for container and virtual machine hosts it operates, including the hypervisor, kernel and container runtime. Where you run your own hypervisor, you configure and evidence residual data handling directly. Where a cloud provider supplies the hypervisor, you inherit part of the control and must still verify the provider's documentation and the settings you control inside guest operating systems and pod workloads.

Third-party managed platforms

Managed databases, serverless runtimes and SaaS components share underlying resources you cannot inspect directly. Scope these by listing each one in the boundary, requesting the provider's SC-4 implementation statement, and recording which clauses the provider covers. Ask for evidence the provider can supply, such as audit records or configuration documentation, and note any gap as a risk to track in the plan of action and milestones.

How an assessor tests SC-4

This table sets out how an assessor works through the two SP 800-53A determination statements for SC-4, grouped by examine, interview and test method. Read each row as a question the assessor asks, the evidence the organization should have ready, and the gaps that most often stop a control from passing. The main takeaway is that SC-4 is judged on proof of behavior at reuse, not on a policy statement alone.

Assessment method	What the assessor checks	Evidence to prepare and common findings
Examine: system design documentation	Whether the design says how memory, storage and registers are cleared or otherwise made unreadable before a new user or process receives them	Architecture and design notes naming the layers involved (hypervisor, operating system, container runtime, storage layer). Finding: design silent on residual data in memory or on reused volumes
Examine: configuration settings and associated documentation	Whether settings that enforce clearing are enabled and documented, such as zeroing or scrubbing options on the platform in use	Exported configuration files, hardening baselines and change records showing when settings were applied. Finding: settings exist in a template but are not confirmed on running hosts
Examine: system audit records	Whether logs show allocation and release events for shared resources and whether unusual reuse activity is recorded	Retained audit records covering storage provisioning and deprovisioning, with retention confirmed. Finding: no logs that tie a released volume to its next consumer
Interview: system and platform administrators	Whether administrators can explain how resources are reclaimed, which teams act on them, and what happens on failure	Named owners, runbooks and a walkthrough of reuse steps. Finding: administrators describe clearing as the cloud provider's job without confirming the provider's behavior in writing
Interview: control owner	Whether one role is accountable for SC-4 across the system and whether that role knows the related controls (AC-3, AC-4, SA-8)	A documented control owner and a responsibility matrix separating provider and organization duties. Finding: unclear ownership of the control across platform and application teams
Test: sampling reused memory, storage or volumes	Whether a resource released by one process or tenant returns no readable prior content to the next consumer	Test records from a sample of reused resources showing zeroed or otherwise unreadable blocks, with method and timestamps. Finding: no proof of zeroing on reuse, only assertions
Test: failure and edge paths	Whether residual data is still cleared when a process crashes, a node is evicted or a snapshot is restored	Test cases and results for abnormal termination and recovery paths. Finding: clearing runs only on normal shutdown

Where residual data actually leaks between users and processes

SC-4 is tested at the points where one user's data can outlive its owner inside shared infrastructure. The most common leak paths are freed heap and stack memory that a new process receives without being cleared, swap and page files that hold memory pages written out of RAM, block storage blocks reallocated to another volume or tenant with old contents still readable, temporary files and caches left in shared directories, and container or virtual machine memory and disks that persist after teardown. Registers saved during context switches can also carry values between processes if the saved state is not isolated. An assessor will ask which of these paths exist in the system boundary and what stops the next user from reading what the previous one left behind.

The two control points are zeroing or sanitizing on release and zeroing or clearing on allocation. Release-time clearing removes the data as soon as a resource is freed, while allocation-time clearing guarantees that a new consumer never sees prior contents, even if an earlier step was skipped. Illustrative example: a container platform that starts a new pod on a node reclaims memory pages from a terminated pod, and the organization must confirm whether the kernel, the container runtime or the hypervisor zeroes those pages before reuse. In most stacks the operating system, hypervisor, cloud platform or storage array supplies the mechanism, so the organization's job is to identify which layer does it, confirm the behavior for each service in scope, and record that confirmation in the system security documentation. Ask the platform owner for the documented sanitization behavior of swap, ephemeral disks and snapshot restore, and test it rather than accept it on trust.

For a self-hosted platform, the practical check is to map each shared resource to the layer responsible for its reuse, then gather configuration evidence that the setting is on. Examine system design documentation and configuration settings for swap encryption or disabled swap, default volume encryption for block storage, and tmpfs and cache cleanup policies. Audit records can show teardown and provisioning events for the same resource. Where a vendor's behavior cannot be confirmed in writing, record that gap in the plan of action and milestones with an owner and a test, rather than leaving the control described only in general terms.

Implementing SC-4 in five steps

This sequence moves SC-4 from a requirement on paper to a documented, tested and monitored control, with each step producing an artifact an assessor can examine. It starts with ownership and ends with a recurring check that the configuration has not drifted.

Name an owner for each shared resource type
Assign a named owner for each category of shared resource that the system uses, such as physical memory, virtual memory, block storage, object storage, caches, registers and temporary files. The platform team usually owns the operating system and hypervisor layers, while the application or database team owns resources that its software allocates and releases. Each owner signs off on the resources in their area. The output is an owner record that maps every resource type to one accountable person or team, which the assessor can use to trace who answers for object reuse.
Inventory the shared resources in scope
List every shared resource in the system boundary where information from one user or process could reach another. Include operating system memory and swap, file systems and volumes, container and virtual machine images, database buffers, message queues, backup media that is reused, and any hardware that moves between tenants or workloads. Record the component, the layer that clears it and the boundary it belongs to. The output is an inventory tied to the system security plan's component list, so no resource is left unassessed.
Confirm the clearing mechanism for each layer
For each inventory entry, confirm how the platform releases and reinitializes the resource before another user or process receives it. Typical mechanisms include zeroing memory pages on allocation or release, wiping or cryptographically erasing volumes before reassignment, and starting containers and virtual machines from clean images. Ask the vendor or your platform documentation to confirm the behavior for your specific versions, because the mechanism differs by layer and product. Export the relevant configuration settings and store them with a note on what each one guarantees. The output is a configuration export per layer.
Test reuse on a non-production copy
Run a reuse test on a non-production copy of the system. Have one process or user write recognizable test data into memory, storage and temporary areas, release those resources, then have a second process or user allocate them and search what it receives for the marker values. Repeat the test for each resource type in the inventory and across container restarts, volume reassignment and VM reuse where those occur. Record the test steps, the observed result and any exceptions, and retain the output. The result is a dated test record that shows whether residual information was exposed, and any failures go back into the remediation plan.
Document the control in the system security plan
Write the SC-4 implementation statement in the system security plan. It should name the responsible owners, describe the clearing mechanism at each layer, reference the configuration exports and test results, and state how the control applies to the system's deployment model. Note any resource that relies on an inherited control from a hosting provider, and cite the agreement or document that defines that inheritance. The output is an updated plan section that matches the inventory and the evidence, so an assessor can compare the written claim against the artifacts without interviewing the team first.
Set a recurring check for configuration drift
Schedule a recurring check that the clearing settings still match the documented configuration and that the reuse test still passes after changes. Compare the current configuration export with the baseline, and review changes to images, hypervisor settings, storage policies and container runtime options. Where your tooling supports it, use policy checks that run against hosts or clusters and report pass or fail for each setting, and route failures to the owner. Confirm the cadence with your own assessment program, since the scope of the control determines how often evidence must be refreshed. The output is a drift report with its review record, kept with the system's continuous monitoring evidence.

Evidence that passes an SC-4 assessment

SP 800-53A asks assessors to examine design documentation, configuration settings and audit records for SC-4, and to test that residual data does not leak between sessions. The cards below cover the artifacts that answer those examine and test steps, and how to keep each one current between assessments.

System design documentation for object reuse

Document where the platform reuses memory, block storage, container file systems and registers between users or processes, and which layer (kernel, hypervisor, storage array or application) is responsible for clearing each one. Name the mechanism per layer, not just the product. Assessors look for a design that explains why residual information cannot reach the next consumer. Keep it current by reviewing it whenever the architecture changes and recording the review date in the document header.

Configuration exports for zeroing settings

Export the effective settings that govern sanitization, such as kernel page zeroing, volume encryption defaults, ephemeral disk wipe behavior and container runtime options that control shared resources. Store each export with a timestamp and the host or cluster it came from. Assessors compare these exports against the design. Schedule the export on a fixed cadence and diff it against the previous run so unexpected drift is visible before an assessment begins.

Audit records showing the control is active

Collect logs that show the sanitization and isolation mechanisms are operating, such as volume provisioning events, pod or VM teardown records and failures reported by the storage layer. Confirm that the audit pipeline captures these events and that someone reviews them. Assessors also check that records are protected from alteration. Ask your logging team to confirm retention and review frequency in writing, since those values are set by your own policy rather than by SC-4.

Test records of residual data reuse

Run a reuse test on a schedule: write a known marker into a memory region, disk block or scratch volume as one tenant or process, release it, then have the next consumer attempt to read it. Record the method, the platform version, the result and the tester. A passing test shows that the design works in practice. Store results with the release they tested so a later change can be compared to the earlier run.

System security plan entry naming the owner

The system security plan should state the SC-4 implementation, the components that carry it and the role accountable for maintaining it. Assessors use this entry to confirm that responsibility is assigned and that the implementation matches the design documents. Review the entry at each assessment cycle and whenever a shared component is added. Confirm with your compliance lead which title and review interval your organization uses.

Change records for platform and storage upgrades

Upgrades to the hypervisor, kernel, container runtime, storage driver or encryption layer can change how memory and disks are cleared. Keep a changelog entry for each platform change that notes whether sanitization behavior was reviewed, and attach the post-upgrade reuse test result. Assessors often ask how the organization knows a patch did not weaken SC-4. A dated changelog with a linked test run answers that question directly.

What meeting SC-4 costs in money and effort

This table breaks down the cost and effort components of meeting SC-4 so you can see who is paid for each part, whether it recurs, and what moves it up or down. NIST does not estimate compliance costs, so use the rows to structure your own quote requests rather than to predict totals. Read the one-time and recurring columns together: the main takeaway is that licence savings from open-source platforms do not remove the engineering and evidence work SC-4 requires.

Cost component	One-time or recurring, and who is paid	What drives it up or down
Platform configuration and sanitization engineering	One-time for the initial baseline, then recurring when platforms change. Paid to the internal platform team or an implementation partner.	Up: number of shared resource types (memory, storage, registers, swap, caches, virtual disks) and number of platforms. Down: one documented platform baseline that sets zeroing or scrubbing behavior for each resource type.
Reuse behavior testing	One-time for the test design, recurring when re-run after upgrades. Paid to internal testers, a security testing firm or both.	Up: managed services where the provider controls memory or storage reuse and the organization cannot inspect it. Down: repeatable test scripts that run on each image build or hypervisor upgrade.
Automated configuration export and evidence capture	One-time to build the export, then recurring as configurations drift. Paid mainly through internal engineering time.	Up: manual screenshots and ad hoc commands. Down: scheduled exports of kernel, hypervisor and storage settings that are stored with a date and an owner.
Evidence upkeep	Recurring. Paid through internal compliance and engineering time, or to a partner who maintains the system security plan entries.	Up: frequent platform changes that are not reflected in the documentation. Down: linking the SC-4 entry to the configuration baseline and change records so updates happen in one place.
External review or independent testing (optional)	Recurring if scheduled, one-time for a single engagement. Paid to a third-party tester chosen by the organization.	Up: scope that covers many platforms, multi-tenant environments or custom hypervisors. Down: a narrower scope tied to the platform baseline, agreed in writing before work starts.
Assessor sampling effort	Recurring at each assessment cycle. Paid through internal staff time to answer requests and produce artifacts; the assessor is paid by the organization for its independent work.	Up: many distinct resource pools to sample, and missing records of configuration history. Down: a short list of platform types with exported settings and test results that show each one.
Open-source licence spend	Usually zero for the software licence itself. Costs remain for hosting, support contracts, and the engineering labor listed above.	Removing licence fees does not remove configuration, testing or evidence effort. Confirm the licence terms of each component in your own environment.

Open-source tools that support SC-4 evidence

None of the tools below proves that memory, storage and registers are cleared between users or processes. Each one produces records that an assessor can use alongside configuration evidence, operating system settings and design documentation for SC-4 Information in shared system resources.

Falco runtime detection

Falco is licensed under Apache-2.0 and parses Linux system calls at runtime, by default through an eBPF probe. Its rules can flag unauthorized file modification, unexpected network connections and suspicious process execution, with container and Kubernetes metadata attached. For SC-4, the useful question is whether a rule would surface a process reading or writing files it should not touch after a resource changes hands. Confirm which rules are active and what they measure in your environment.

GitLab container scanning with Trivy

GitLab Community Edition is licensed under MIT. Its container scanning job uses Trivy to find vulnerabilities in images, including base images and OS packages, and writes a JSON report plus a CycloneDX SBOM as job artifacts. These records show what software a container image carries and where it came from, which helps assessors confirm that shared base images do not leave residual data or components behind. Scanning does not inspect runtime memory or storage reuse, so confirm that with your own tests.

Wazuh configuration assessment

Wazuh is licensed under GPL-2.0-only. Its Security Configuration Assessment applies YAML policies, mostly based on CIS benchmarks and extendable with custom checks, to files, directories, registry keys and running processes on monitored endpoints. Custom policies can check the kernel and system settings that govern memory and storage handling on your hosts, and report remediation steps for failures. Confirm that the policies you run actually cover the settings your SC-4 design relies on, because the default content is not written for SC-4.

Fleet device policies

Fleet is licensed under MIT. Its policies ask yes or no questions of devices as osquery queries, and the policies page shows which devices in each fleet pass or fail each policy. A policy can check whether disk encryption is on, swap or temporary storage is configured as the design expects, or a host is running an approved image. Passing results give a dated, per-device record for an assessor. Each policy must be written to test the actual SC-4 requirement, which Fleet does not decide for you.

Who owns SC-4 and who prepares its evidence

Your organization owns SC-4. That means accountability for deciding how information in shared system resources is protected, for approving the configuration that enforces it, and for recording the control in the system security plan. Outsourcing preparation does not transfer ownership, and an assessor will ask the accountable owner, not the implementer, to explain the design.

Control ownership: Name an accountable owner for SC-4 and document who approves changes to the memory, storage and register handling that the control relies on.
Platform configuration decisions: Decide which platforms, hypervisors, container runtimes and storage services fall in scope and which reuse mechanisms they must enforce.
System security plan entry: Write or approve the SC-4 implementation statement, including how it is inherited from a cloud provider or shared platform where that applies.
Scope decisions: Decide which system components and data classes are in the boundary, since the reuse question depends on what shares resources.
Exception handling: Own any residual risk accepted when a provider or component cannot demonstrate clearing behavior.

Before engaging anyone, confirm internally who signs the SC-4 entry and who can answer an assessor's questions about system design.

Questions teams ask about SC-4 cost, time and effort

Is SC-4 more work than other SC controls?

SC-4 is usually less work than boundary protection or cryptographic controls, because it has no organization-defined parameters and only one active enhancement that is not assigned to an SP 800-53B baseline. The effort sits in proving a negative: that memory, storage and registers released by one user or process cannot expose data to the next. SC-7 and SC-8 demand network design, traffic rules and encryption configuration across many components, while SC-4 concentrates on how the platform reuses shared resources. Its size depends on how many shared environments you run, such as multi-tenant hypervisors, shared Kubernetes nodes, pooled storage and reused virtual disks. Confirm the component list with your assessor before estimating effort.

Can our team meet SC-4 without outside help?

Often yes, if your engineers understand how the operating system, hypervisor and storage layer clear resources between tenants or sessions. The harder part is producing evidence an assessor can examine: design documentation, configuration settings and audit records that show the behavior is intended and monitored. Teams that lack platform or storage specialists, or that run shared resources across several business units, often bring in help to map components, document the design and set up repeatable checks. DeployOpen prepares systems, configurations and evidence for assessments, but the organization owns the control and an independent assessor determines whether it is met.

What does SC-4 need from platform and storage owners?

SC-4 needs owners of shared infrastructure to state how released resources are cleared before reuse. Platform owners typically confirm hypervisor and container runtime behavior, memory scrubbing defaults and how nodes are recycled between workloads. Storage owners confirm that new or reallocated volumes, snapshots and deleted blocks do not return prior data, and that encryption at rest or secure erase is applied where relevant. Each owner should provide:

Configuration settings that enforce clearing or encryption, with their change history
Design documentation describing shared resource pools and reuse paths
Audit records or test results that show the behavior works in practice

Agree these deliverables and owners in writing at the start of the work.

How long does SC-4 work take?

Duration depends on scope: how many shared environments are in play, how documented the existing design is, and how much testing your assessor expects. DeployOpen does not publish timelines. Most engagements are fixed-scope, so scope, deliverables and timelines are agreed in writing before work starts, and a quote follows from that written scope. To narrow the estimate, list every shared resource type in the system boundary and note which of them already have documented clearing behavior. Ask any partner to show how the timeline maps to each deliverable.

Do cloud providers handle SC-4 for us?

Cloud providers handle part of SC-4 for the infrastructure they operate, but not all of it. Their shared responsibility documentation generally covers hypervisor and physical resource reuse, while your team still owns guest operating systems, container images, application memory handling, volumes you create and snapshots you retain. Review the provider's published documentation for each service in scope and map which parts of the control they cover. Where the provider documentation does not state clearing behavior clearly, ask the provider directly and record the answer. Your assessor will expect you to show which responsibilities are inherited and which are yours.

How do we keep SC-4 evidence current?

Treat SC-4 evidence as a recurring output of configuration management, not a one-time document. Store clearing and encryption settings as code or versioned configuration, and re-collect the evidence after every platform upgrade, new node image or storage change. Runtime monitoring can help: Falco parses Linux syscalls through an eBPF probe by default, and Wazuh Security Configuration Assessment checks endpoint configuration against YAML policies that can be extended with custom checks. Fleet policies ask yes or no questions of devices and show which ones pass or fail. Confirm each tool's coverage for your specific resource types before relying on it as evidence.

Who signs off that SC-4 is met?

The organization decides whether it accepts the control as implemented, and its authorizing official or equivalent accountable executive takes responsibility for the residual risk. The assessment itself is performed by an independent assessor, whose report states the findings. An implementation partner, including DeployOpen, prepares systems, controls and evidence but does not issue audit reports, attestations or certifications. Confirm with your contracting authority or regulator which assessor role they recognize, since requirements differ between federal, FedRAMP and contractual contexts.

What should a fixed-scope SC-4 quote include?

A fixed-scope quote should state exactly what is in and out of scope, and it should name the deliverables before it names a price. Ask for:

The list of shared resource types in the boundary, such as hypervisors, container nodes, storage pools and backup targets
The evidence package for each, with the configuration, design documents and test results to be produced
Who performs each task and what you must provide, such as access, change windows and named owners
Assumptions about existing documentation, cloud provider responsibilities and assessor expectations
Acceptance criteria and the handover format for evidence

Request a written scope and not a verbal estimate, because pricing and timing should follow directly from it.

How DeployOpen scopes and prepares SC-4 evidence

DeployOpen is a Chainscore Labs company that implements self-hosted open-source platforms inside the client's own infrastructure. For SC-4 Information in shared system resources, we prepare the systems, configuration and evidence an independent assessor will examine, while the organization owns the control and the assessor issues any findings.

How we scope

We agree in writing which systems, shared resources and hosting environments fall under the SC-4 scope.
We confirm with you which SP 800-53B baseline and system boundary apply before any work starts.
Engagements are fixed-scope, with deliverables and timelines written down ahead of implementation.

How we build

We configure memory, storage and register reuse settings on the platforms in scope, documenting each setting.
We test that residual data is cleared between users and processes using repeatable, scripted checks.
We set up runtime monitoring for unexpected cross-process data access and retain the resulting audit records.

How we hand over

We deliver system design documentation and configuration baselines that describe how object reuse protection works.
We provide test results and audit record samples mapped to the SC-4 assessment objects your assessor will request.
We confirm with your assessor which evidence formats they accept before the handover is final.

How we support

Ongoing support, upgrades and continuous testing are available as a retainer after handover.
We re-run residual information checks after platform upgrades or changes to the shared hosting environment.
Your organization remains responsible for the control, so we agree in writing who maintains each evidence item.