CM-5(6): Limit Library Privileges

CM-5(6): Limit Library Privileges requires you to tightly restrict who can change software stored in “software libraries” (your approved repositories, package registries, golden image stores, and artifact repos) so only explicitly authorized roles can modify what gets built and deployed ¹. Operationalize it by locking down write access, enforcing change workflows, and keeping auditable logs.

Key takeaways:

• Treat “software libraries” as production-adjacent crown jewels: restrict write privileges to a small, approved set of maintainers ¹.
• Enforce controlled change paths (PRs, approvals, CI/CD gates) so changes are attributable and reviewable.
• Keep evidence that proves who can write, how changes are approved, and what changed, across every library that feeds production.

CM-5(6) is a deceptively small requirement with outsized operational impact: it targets the point where software becomes “official” for your environment. In practice, that means your artifact repositories, container registries, package repos, internal libraries, base images, and any “golden” software distribution points that developers and deployment pipelines pull from. If the wrong person, service account, or compromised credential can overwrite those contents, you can end up deploying unreviewed code while your normal application controls still look “green.”

For a Compliance Officer, CCO, or GRC lead, the fastest path to implementation is to scope what counts as a software library, assign a single accountable owner, and force all changes through controlled, logged mechanisms. You do not need to boil the ocean. You need provable restrictions on write privileges and clear evidence that the restrictions are enforced, reviewed, and monitored.

This page translates the cm-5(6): limit library privileges requirement into specific operational steps, audit-ready artifacts, and a practical execution plan aligned to NIST SP 800-53 Rev. 5 ².

Regulatory text

Requirement (excerpt): “Limit privileges to change software resident within software libraries.” ¹

Operator interpretation: You must ensure only a restricted, explicitly authorized set of identities (people and service accounts) can modify software stored in repositories and library locations that feed builds, deployments, or enterprise distribution. This is a permissions and workflow control: minimize who can write, require traceable changes, and preserve evidence that access is controlled and reviewed ¹.

Plain-English interpretation (what it really means)

A “software library” is any place your organization treats as a source of approved software artifacts. Typical examples:

• Source code repos for shared libraries and deployment manifests
• Artifact repositories (binary repositories)
• Container registries and base image repositories
• Internal package registries
• Golden images / VM templates
• Configuration “libraries” that drive infrastructure-as-code

CM-5(6) focuses on change privilege. Read access can be broad in many environments; write access must be narrow and governed. If an attacker (or a well-meaning engineer) can bypass review and directly modify library contents, you lose integrity of the software supply chain.

Who it applies to

Entities: Federal information systems and contractor systems handling federal data ¹.

Operational contexts where auditors will expect coverage:

• Any system boundary where you claim NIST SP 800-53 alignment ²
• DevSecOps environments that produce artifacts for production
• Central IT teams maintaining “standard” images, endpoint software catalogs, or enterprise packages
• Third-party-supported repositories where external maintainers have access (still your risk)

Key roles:

• Control owner: typically AppSec, Platform Engineering, or Configuration Management
• Library administrators: repo/registry admins with permission to grant access
• Change approvers: code owners, release managers, CAB (if applicable)
• Identity owners: IAM team managing groups, RBAC, and service accounts

What you actually need to do (step-by-step)

1) Define and inventory “software libraries” in scope

Create a definitive list of repositories/registries that qualify as software libraries for your boundary. Include:

• System name, owner, platform (Git, artifact repo, container registry)
• Environment (prod, non-prod, shared services)
• What consumes it (CI/CD, production hosts, other apps)
• Authentication method (SSO, tokens, keys)

Execution tip: Start with the few that can affect production. If it can be deployed or pulled into a build, treat it as in scope.

2) Establish privilege tiers and a default-deny stance for write access

Define roles with clear intent. A workable model:

• Reader: can pull/clone/download
• Contributor: can propose changes via PR/MR, cannot directly write to protected branches/tags
• Maintainer/Publisher: can publish artifacts or merge to protected branches, tightly limited
• Admin: can change permissions and protection rules, extremely limited

Then implement default deny for write privileges: nobody gets publisher/maintainer/admin by default; they must be explicitly approved.

3) Implement technical controls that prevent unreviewed changes

Pick controls that your platforms can enforce reliably:

For source code libraries (Git-based):

• Protect main/release branches from direct pushes
• Require pull requests/merge requests
• Enforce required reviewers and/or CODEOWNERS
• Restrict who can create or update release tags
• Require signed commits or verified build provenance if available (keep focus on privilege limitation as the primary objective)

For artifact repositories and package registries:

• Restrict “publish” or “upload” permissions to a small group and CI service accounts
• Prefer CI-based publishing over human publishing
• Block overwrite of existing versions where supported (prevents “replace in place” attacks)
• Require scoped tokens with least privilege

For container registries and base images:

• Restrict push to production namespaces
• Control who can mark images as “trusted” or “golden”
• Gate promotion from staging to production registries through CI

4) Control and monitor service accounts (common failure point)

Most organizations lock down humans and forget the robot identities. Require:

• Dedicated CI/CD service accounts per pipeline or per product line
• Short-lived credentials where supported; otherwise rotate and scope tokens
• Explicit mapping between service account permissions and the pipeline/job that needs them
• Separation between “build” identities and “admin” identities

5) Add an access approval and periodic review process

Operationalize with a lightweight workflow:

• Access request ticket with business justification and duration (if you use time-bound access)
• Approval by the library owner plus security or platform owner (two-person integrity where feasible)
• Periodic access review of all publisher/admin roles for each library, with documented removals

6) Centralize logging and make changes attributable

Ensure you can answer:

• Who changed the artifact/library contents?
• When did it change?
• What mechanism allowed the change (PR merge, direct push, upload API)?
• Which identity performed it (person or service account)?

At minimum, retain audit logs from the repo/registry platform and IAM logs for permission changes.

7) Document the control and map it to an owner and evidence set

Auditors do not grade intent. They grade design and operation. Write a short procedure:

• Scope definition (what “software libraries” means for you)
• Roles and permission model
• Required workflows for change
• Logging and review cadence
• Exception handling (break-glass)

Daydream (as a GRC workflow system) fits naturally here by storing the control narrative, ownership, recurring evidence requests, and review attestations so you can produce an assessment-ready packet without rebuilding it each cycle.

Required evidence and artifacts to retain

Keep evidence that proves both restriction and operation:

Access control evidence

• Current access lists for each library/registry (export showing who has write/admin)
• IAM group definitions and membership for “publishers” and “admins”
• Screenshots or config exports of branch protection / repository rules

Change control evidence

• Sample of merged PRs showing required approvals
• CI/CD job configuration demonstrating publishing path uses a service account
• Registry configuration showing immutability/overwrite protections (if configured)

Monitoring and auditability

• Audit logs for repository/registry actions (push, tag, publish, permission changes)
• Central log retention configuration or SIEM forwarding proof
• Evidence of periodic access review and resulting removals

Governance

• Written procedure for CM-5(6) implementation, assigned owner, and exception process ¹

Common exam/audit questions and hangups

Expect assessors to ask:

• “List all software libraries in scope. How did you determine completeness?”
• “Who can publish artifacts or push to protected branches today? Show me.”
• “How do you prevent direct pushes or overwriting released artifacts?”
• “How do you control CI/CD service accounts that have publish permissions?”
• “Show evidence of access reviews and deprovisioning.”
• “How do you detect and respond to unauthorized changes in repositories/registries?”

Hangups that slow audits:

• “Software library” scope ambiguity (teams argue whether Git counts, whether non-prod counts)
• Overreliance on policy text without permission exports and logs
• Orphaned admin accounts and legacy groups nobody owns

Frequent implementation mistakes (and how to avoid them)

1. Treating Git as out of scope. If production builds pull from it, it’s a software library in effect. Include it.
2. Too many maintainers. If everyone can publish, nobody controls integrity. Cap publisher roles and justify each one.
3. Service accounts with admin permissions. CI should publish, not administer. Split duties.
4. No control on tags/releases. Tagging can be a release mechanism. Protect it like a production deploy.
5. Evidence gaps. Strong controls without exports, logs, and review records still fail an assessment. Define recurring evidence up front.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement. Practically, CM-5(6) maps to software integrity and supply chain risk: if library write access is broad or unmonitored, an attacker can insert malicious code or backdoored artifacts that propagate through normal deployment channels. The business impact usually shows up as incident response scope expansion, loss of system integrity, and prolonged recovery because you can’t trust what was deployed.

Practical 30/60/90-day execution plan

First 30 days (stabilize scope and stop the bleeding)

• Name the control owner and system owners for each library ¹.
• Inventory software libraries that feed production builds/deployments.
• Export current write/admin access lists; identify “everyone can write” hotspots.
• Implement immediate restrictions: remove broad write access, protect main/release branches, restrict registry push to a small group and CI accounts.
• Turn on and retain audit logs for repo/registry and permission changes.

Days 31–60 (standardize controls and approvals)

• Create a standard permission model (reader/contributor/publisher/admin) and apply it consistently.
• Require PR approvals and enforce branch protection across all in-scope repos.
• Move publishing to CI/CD where humans still publish manually.
• Stand up an access request workflow with required approvals and documented justifications.
• Begin a recurring access review cycle for publisher/admin roles, with tracking in your GRC system.

Days 61–90 (prove operation and harden exceptions)

• Run the first formal access review and record results (adds strong audit credibility).
• Implement immutability/anti-overwrite controls in artifact repos where supported.
• Tighten service account governance: scoped tokens, rotation process, owner assignment.
• Define break-glass access with approval, logging, and post-event review.
• Build an “assessment packet” in Daydream: scope list, procedure, permission exports, sample PRs, logs, and review attestations.

Frequently Asked Questions

What counts as a “software library” for CM-5(6)?

Any repository or registry that stores software artifacts or code that your organization treats as approved inputs to builds or deployments qualifies ¹. If production can consume it directly or indirectly, include it in scope.

Do I have to remove all developer write access?

You need to limit privileges to change software in the library, so broad write access is hard to justify ¹. A common pattern is to allow developers to propose changes via PRs but restrict direct writes to protected branches and restrict publishing rights.

Are CI/CD service accounts allowed to publish to registries?

Yes, if the account is explicitly authorized, scoped to the minimum permissions required, and monitored with audit logs. Auditors will want to see that the service account cannot grant permissions or bypass controls.

How do we handle emergency fixes?

Use a break-glass process: time-bound elevated access, explicit approval, mandatory logging, and a post-change review that confirms the change was appropriate and access was removed. Keep the ticket and logs as evidence.

What evidence is most persuasive to an auditor?

Permission exports showing limited write/admin access, branch protection or registry rule configurations, and audit logs that tie changes to specific identities are the fastest “proof” set. Pair that with documented access reviews to show the control operates over time.

We use third parties to manage parts of our build pipeline. Does CM-5(6) still apply?

Yes. If a third party can change your software libraries, you still need to govern and monitor that access inside your boundary and contractually where applicable. Treat third-party identities like any other privileged identity and require the same evidence.

Footnotes

1. NIST SP 800-53 Rev. 5 OSCAL JSON

2. NIST SP 800-53 Rev. 5