A vendor may sell a proprietary product while most of its software stack contains open source components. That is normal and can accelerate secure innovation. The risk comes from weak visibility, careless package selection, untrusted build inputs, abandoned dependencies, delayed remediation, or an inability to tell customers which deployed versions are affected by a new vulnerability.
TPRM teams do not need to review every line of source code. They do need evidence that the vendor governs the software it consumes, knows what is in each released product, protects the build process, monitors emerging risk, and can remediate or contain affected components within timeframes that match the service’s criticality. This guide turns open source assurance into practical questions and decision records.
What Open Source Risk Actually Includes
Open source risk is broader than a list of known vulnerabilities. A third-party product can be exposed through direct packages, transitive dependencies, build tools, containers, operating-system libraries, code copied into the repository, models, plugins, or hosted services. Key risk domains include:
- Known vulnerabilities: exploitable weaknesses in a component or its dependencies.
- Malicious packages: dependency confusion, typosquatting, account takeover, or intentionally harmful releases.
- Maintenance health: unsupported, abandoned, or single-maintainer components with no practical replacement plan.
- Provenance and integrity: uncertainty about where an artifact came from, who changed it, and whether the build was protected.
- Patch capability: inability to identify affected releases, prioritize exposure, test fixes, or ship updates quickly.
- License and obligation risk: incompatible terms, missing notices, source-disclosure obligations, or restrictions that affect distribution.
- Visibility gaps: incomplete inventories, stale SBOMs, missing transitive dependencies, or mismatches between build and production.
The assessment should distinguish component risk from product exposure. A critical CVE in an inventory is important, but reachability, configuration, compensating controls, data flow, privilege, and deployed version determine the actual impact. Conversely, a component with no published CVE can still create risk if it is unmaintained or its release channel is compromised.
Where TPRM Responsibility Starts And Stops
Engineering and product security own technical implementation. TPRM owns the third-party decision: whether the vendor’s governance and evidence are sufficient for the proposed use. The analyst should connect technical facts to service criticality, data sensitivity, access, exposure, contract rights, incident duties, and remediation commitments.
A low-risk internal tool does not need the same depth as an internet-facing platform with privileged access to production data. Apply tiering first. Then request evidence proportional to the risk and involve application security, architecture, legal, privacy, procurement, or open source counsel where specialist judgment is required.
Evidence To Request
A product-specific SBOM
Request a software bill of materials for the product and version being assessed. It should use a machine-readable format such as SPDX or CycloneDX, include direct and transitive components where possible, identify versions and package origins, and state when and how it was generated. Confirm whether the SBOM represents source, build, release, container, or deployed runtime. Those inventories can differ.
Open source governance
Look for a policy covering component selection, approved sources, license review, security review, version pinning, updates, exceptions, end-of-life handling, and developer education. Ask who owns the program and how policy violations are detected. A policy without inventory, tooling, and accountable owners is weak evidence.
Software composition analysis and continuous monitoring
The vendor should scan source, manifests, lock files, containers, and release artifacts at appropriate stages. Ask how findings are deduplicated, validated, prioritized, and linked to deployed products. CISA’s software supply-chain guidance recommends validating supplier SBOMs with software composition analysis and continuously monitoring relevant vulnerability sources.
Vulnerability response and VEX
Review patch SLAs, severity methods, exploit intelligence, customer notifications, emergency release processes, and exception approval. A Vulnerability Exploitability eXchange statement can communicate whether a product is affected, not affected, fixed, or under investigation. Treat VEX as a signed, scoped assertion to evaluate, not a reason to ignore a vulnerable component.
Build integrity and provenance
Ask how the vendor protects source repositories, package registries, CI/CD runners, signing keys, build credentials, and release approvals. Useful evidence can include branch protection, peer review, isolated builds, signed artifacts, provenance attestations, protected registries, dependency pinning, reproducible-build practices, and traceability from source commit to released artifact.
Maintenance and substitution planning
Determine how the vendor identifies abandoned projects, evaluates maintainer health, and replaces critical dependencies. For components essential to the product, ask whether the vendor can upgrade, fork, fund, isolate, or remove the dependency. “The community will fix it” is not a recovery strategy.
License and distribution controls
Security review does not replace license review. Confirm that the vendor inventories licenses, evaluates obligations, maintains notices, controls prohibited licenses, and can respond to claims. Escalate complex compatibility or distribution questions to qualified legal counsel.
How To Validate An SBOM
An SBOM is useful only when it is complete enough, current enough, and connected to operational response. Check the product name, version, generation date, format, component identifiers, versions, hashes, dependency relationships, supplier information, and scope. Ask whether dynamically loaded packages, operating-system components, containers, build dependencies, and vendored code are included.
Then test the process, not just the file. Select a small sample of components and ask the vendor to show the source, approved version, scan result, exposure conclusion, owner, and update history. Choose one recent high-profile vulnerability and ask how the vendor determined whether specific customer versions were affected. This reveals whether the inventory supports decisions.
| Control area | Useful evidence | Warning sign |
|---|---|---|
| Inventory | Version-specific SBOM generated from the release | One generic spreadsheet for all products |
| Selection | Approved-source policy, health checks, exceptions | Developers install any package directly from the internet |
| Integrity | Signed artifacts, protected builds, provenance | No traceability from source to customer release |
| Monitoring | SCA coverage, alerts, reachability analysis, owners | Annual scanning only |
| Remediation | Patch SLA results and validated emergency process | Targets exist but performance is not measured |
Questions To Ask Before Approval
- Which product releases have complete, machine-readable SBOMs, and how soon after release are they available?
- How do you discover direct, transitive, container, operating-system, and build-time dependencies?
- Which repositories and registries are approved, and how are malicious or substituted packages blocked?
- How are components evaluated for security, maintenance activity, ownership, popularity, and license obligations?
- How do you determine whether a vulnerable component is reachable or exploitable in the product?
- What are your remediation targets, actual performance, exception process, and customer notification thresholds?
- Can you trace a customer release to source, dependency set, build system, approvals, and signed artifact?
- What happens when a critical project is abandoned, compromised, relicensed, or removed?
Eight-Step Open Source Assessment Workflow
- Tier the use case. Record product criticality, exposure, data, privileges, deployment model, users, and recovery needs.
- Define the evidence scope. Name the exact product, edition, version, hosting model, and release channel under review.
- Assess governance. Review ownership, policy, approved sources, license controls, developer practices, and exception authority.
- Validate inventory. Inspect the SBOM’s format, date, coverage, relationships, and connection to the released artifact.
- Test monitoring and triage. Sample vulnerabilities and confirm discovery, exposure analysis, severity, ownership, and customer communication.
- Review build trust. Evaluate repositories, CI/CD, registry controls, signing, provenance, credentials, and release approval.
- Decide and document. Record gaps, compensating controls, residual risk, contractual commitments, owners, and deadlines.
- Monitor change. Reassess after major releases, incidents, critical dependency changes, acquisitions, end-of-life notices, or missed remediation targets.
Contract And Monitoring Considerations
Where the risk justifies it, contracts can require secure development practices, product-specific SBOM delivery, timely vulnerability notifications, remediation targets, support periods, change notices, incident cooperation, audit evidence, and obligations that flow to relevant subcontractors. Be precise about format, product version, timing, confidentiality, and how emergency risk is communicated.
Ongoing monitoring should prioritize material changes rather than generate an endless vulnerability feed. Track critical exploitable vulnerabilities affecting deployed versions, repeated SLA breaches, unsupported components, compromised maintainers or registries, major architecture changes, SBOM quality, security incidents, and overdue remediation. Connect each alert to an owner and a decision rule.
Red Flags That Need Escalation
- The vendor cannot produce an SBOM for the assessed product version.
- The inventory excludes transitive dependencies or production containers without explanation.
- Scanning occurs only before an annual audit or customer request.
- Critical findings are closed because “open source is community maintained.”
- The vendor has no process for malicious packages, registry compromise, or dependency confusion.
- Patch targets exist, but actual remediation performance and exceptions are not tracked.
- Build artifacts are unsigned and cannot be traced to reviewed source.
- A core dependency is unsupported and no replacement, isolation, or fork plan exists.
Common TPRM Mistakes
Treating every CVE as equal
Use severity, exploitability, reachability, exposure, asset criticality, controls, and deployed version. A long unfiltered list creates noise and can hide the finding that actually affects the service.
Accepting an SBOM as proof of security
An inventory is foundational evidence, not a conclusion. Verify how it is generated, how accurately it reflects releases, and whether the vendor uses it to respond.
Ignoring build and package provenance
A component may have no known vulnerability while the acquisition or build path is compromised. Review trusted sources, integrity checks, signing, and protected build processes.
Requesting sensitive detail without a decision use
Large SBOMs and scan exports create storage and confidentiality obligations. Define who will analyze the data, how it will be secured, how long it will be kept, and what action thresholds apply.
Leaving ownership entirely with procurement
Procurement can secure commitments, but product security, engineering, legal, TPRM, and the business owner may all be needed to interpret evidence and accept residual risk.
Analyst Takeaway
Open source is not itself a control failure. The decision depends on whether the vendor can identify what it ships, trust where it came from, detect emerging risk, explain product exposure, and remediate at a pace that matches the service. Start with a product-specific SBOM, then validate the governance and operating process behind it. The final assessment should state which version was reviewed, which evidence was relied on, what remains uncertain, and who owns every condition of approval.
Frequently Asked Questions
Should TPRM require an SBOM from every vendor?
Use a risk-based threshold. Software suppliers supporting critical, internet-facing, privileged, regulated, or sensitive processes are stronger candidates. For low-risk services, lighter assurance may be proportionate.
Which SBOM format is best?
SPDX and CycloneDX are widely used machine-readable formats. The best choice is one the vendor can generate accurately and the customer can process. Scope, identifiers, versions, relationships, and freshness matter more than a logo on the file.
Does a VEX document replace vulnerability analysis?
No. VEX communicates a supplier’s status for a vulnerability in a product. Review its scope, product version, justification, status, signature or provenance, date, and supporting evidence.
How often should open source evidence be refreshed?
SBOMs should align with relevant releases, while vulnerability monitoring should be continuous. Refresh the TPRM conclusion after material releases, incidents, missed patch targets, major dependency changes, or changes in product criticality.
Authoritative Sources
- NIST SP 800-218: Secure Software Development Framework
- CISA: Managing Open Source Software and Software Bills of Materials
- European Commission: Cyber Resilience Act and open source software
- OpenSSF Concise Guide for Evaluating Open Source Software
- OpenSSF Open Source Project Security Baseline
- NIST SP 800-161 Rev. 1: Cybersecurity Supply Chain Risk Management
