Skip to main content
Oversight Institute
Category: Software Supply Chain Security

Hardware Bill of Materials

Also known as: HBOM, hardware BOM
Simply put

A Hardware Bill of Materials (HBOM) is a structured list of the physical components used to build a hardware product. It gives purchasers and asset owners a way to see what is inside the products they buy, which can help them evaluate and address supply chain risks. Requesting an HBOM is one of several activities a purchaser can use to understand a supplier's hardware, though it is not on its own a complete risk assessment.

Formal definition

An HBOM is a standardized inventory that enumerates the physical components incorporated into a hardware product, intended to support cyber supply chain risk management (C-SCRM). The HBOM Framework, developed by the Hardware Bill of Materials Working Group under CISA, establishes a consistent naming approach and a repeatable, structured method for vendors to communicate hardware component information to purchasers. In practice, requesting HBOMs is one of multiple due-diligence activities purchasers may leverage to evaluate supply chains and mitigate risk; it is not a certification, an attestation of security, or a substitute for broader assessment. The HBOM addresses hardware component transparency and is distinct from a Software Bill of Materials (SBOM), which enumerates software components; the two are complementary rather than interchangeable. Scope, completeness, and the depth of supplier tiers reflected in an HBOM can vary, and its usefulness depends on the accuracy and currency of the information the vendor provides.

Why it matters

Hardware supply chains often extend across multiple tiers of component suppliers, and purchasers frequently have limited visibility into what physical parts are actually inside the products they acquire. An HBOM addresses this gap by giving purchasers and asset owners a structured way to see the components that make up a hardware product, which can support cyber supply chain risk management (C-SCRM) activities such as identifying components sourced from suppliers of concern or assessing exposure when a component is later found to be problematic. Without this transparency, organizations may struggle to answer basic questions about what they have deployed.

The HBOM Framework developed by the Hardware Bill of Materials Working Group under CISA responds to a practical problem: vendors and purchasers have historically lacked a consistent, repeatable way to communicate hardware component information. By establishing a consistent naming approach and a structured method, the framework aims to make component data more comparable across suppliers and easier to act on.

It is important to keep the HBOM's role in perspective. Requesting an HBOM is one of several activities a purchaser can use to evaluate a supply chain, not a complete risk assessment in itself. An HBOM is not a certification, and it does not constitute an attestation that a product is secure. Its value depends heavily on the accuracy, completeness, and currency of the information the vendor supplies, and the depth of supplier tiers reflected can vary considerably. Purchasers should treat it as an input to due diligence rather than as a guarantee.

Who it's relevant to

Procurement and Supplier Due-Diligence Teams
Procurement and sourcing teams may request HBOMs from hardware vendors as one input among several during supplier evaluation and onboarding. An HBOM can help these teams understand what components are inside a product, but it should be paired with broader assessment activities, since it is not itself a full risk assessment or an attestation of security.
Cyber Supply Chain Risk Management (C-SCRM) Practitioners
C-SCRM practitioners can use HBOM data to identify component-level exposure, such as reliance on suppliers of concern, and to support mitigation planning. Because the depth of supplier tiers and the completeness of an HBOM can vary, practitioners should weigh how much visibility a given HBOM actually provides beyond the first tier.
Asset Owners and Operators
Asset owners and operators deploying hardware products benefit from knowing what physical components they have in their environment, which can support responses when a specific component is later found to be problematic. The usefulness of the HBOM for this purpose depends on the accuracy and currency of the vendor-provided data.
Hardware Manufacturers and Vendors
Manufacturers and vendors are the parties who compile and communicate HBOMs. Adopting the consistent naming approach and structured method in the CISA HBOM Framework can make it easier to respond to purchaser requests in a comparable, repeatable way, though producing an HBOM does not certify a product as secure.

Inside HBOM

Component identification
Structured records of the discrete hardware elements within a product, which may include integrated circuits, semiconductors, printed circuit board assemblies, connectors, and other electronic and mechanical parts, typically identified by part numbers and reference designators.
Manufacturer and supplier attribution
Information on the entities that produce or supply each component, which can help trace direct suppliers and, where visibility permits, upstream sources; visibility often diminishes beyond the first tier of the supply chain.
Provenance and sourcing data
Attributes describing where and by whom components were made, intended to support authenticity and counterfeit-detection efforts, though the completeness of such data depends on what suppliers disclose and can independently be verified.
Version and revision identifiers
Details distinguishing component revisions, lot or date codes, and hardware versions, which are relevant because a given HBOM typically reflects a point-in-time configuration that can change across production runs.
Structural relationships
Hierarchical or assembly relationships showing how components combine into subassemblies and finished products, which support impact analysis when a specific part is implicated in a risk.

Common questions

Answers to the questions practitioners most commonly ask about HBOM.

Is an HBOM the same thing as a Software Bill of Materials (SBOM)?
No. An HBOM inventories the physical components, parts, and assemblies that make up a hardware product, whereas an SBOM inventories software components and dependencies. While both support supply chain transparency, they cover distinct layers of a product. A given device may have both, and firmware or embedded software within hardware is typically documented separately in an SBOM rather than folded into the HBOM. Treating one as a substitute for the other leaves gaps in visibility.
Does producing an HBOM mean an organization has secured its hardware supply chain?
No. An HBOM is an inventory and transparency artifact; it documents what components are present but does not by itself assess, mitigate, or eliminate risk. Visibility into component provenance can support risk assessment, counterfeit detection, and sourcing decisions, but the HBOM is an input to those processes rather than a control that secures the supply chain. Its value depends on how the data is validated, kept current, and acted upon, and an HBOM alone does not confer any certification or compliance guarantee.
How deep into the supply chain should an HBOM go?
Depth depends on the risk tier and the intended use of the HBOM. Many programs begin with first-tier components and struggle to obtain reliable visibility into lower tiers or sub-assemblies sourced by suppliers. Because complete Nth-tier decomposition is often impractical, organizations typically define the level of granularity by criticality, such as prioritizing components with security, safety, or single-source implications. Stating the intended depth and its boundaries up front helps set realistic expectations for downstream users of the data.
How should HBOM data be kept current after a product ships?
An HBOM reflects the component composition at a point in time and can become stale as suppliers substitute parts, address shortages, or issue revisions. In many programs, refresh triggers are tied to engineering change orders, revision releases, or supplier-notified component substitutions rather than a fixed calendar. Because point-in-time inventories degrade in accuracy over time, defining update triggers and version control for the HBOM is generally as important as producing the initial document.
What format should be used to capture and exchange an HBOM?
There is no single universal format, and practices vary across sectors and toolchains. Some organizations extend structured formats also used for SBOMs to accommodate hardware fields, while others rely on spreadsheets or supplier-provided documentation. The practical consideration is whether the chosen format captures the fields needed for the intended use, such as part identifiers, provenance, and sourcing details, and whether it can be exchanged and parsed by the parties who need it. Format choice should follow the use case rather than being adopted in isolation.
How can the accuracy of supplier-provided HBOM data be validated?
Much HBOM data is self-reported by suppliers, and an attestation of contents is not the same as independent verification. Depending on the risk tier, programs may corroborate reported data through inspection, testing, component authentication, or reconciliation against procurement and engineering records. Where independent validation is not feasible, the reliance on self-reported information should be documented as a known limitation, since unverified data can carry gaps or inaccuracies that the HBOM itself does not surface.

Common misconceptions

An HBOM is simply the hardware equivalent of a Software Bill of Materials (SBOM) and can be treated the same way.
While both are inventories of constituent parts, they address distinct domains. An HBOM catalogs physical hardware components and their sourcing, whereas an SBOM catalogs software components and dependencies. The two are complementary rather than interchangeable, and a program focused on one does not cover the risks addressed by the other.
An HBOM gives complete visibility into the full multi-tier supply chain for a product.
HBOM data is often strongest for directly contracted suppliers and components, but visibility typically diminishes beyond the first tier. Coverage depends on what suppliers disclose, and gaps in fourth-party or Nth-party sourcing commonly remain.
Producing an HBOM verifies component authenticity and eliminates counterfeit risk.
An HBOM is primarily an inventory and, where sourcing data is included, can support counterfeit-detection efforts. It does not by itself constitute independent verification of authenticity, and self-reported or point-in-time data can become stale or incomplete.

Best practices

Treat the HBOM as a point-in-time artifact and establish a process to refresh it as component revisions, lot codes, and suppliers change across production runs.
Where feasible, corroborate supplier-provided sourcing and provenance data through independent verification rather than relying solely on attestations.
Document known visibility limits explicitly, noting where data extends only to the first tier and where fourth-party or Nth-party sourcing is unknown.
Maintain the HBOM alongside, but distinct from, any SBOM so that hardware and software risks are each addressed within their proper scope.
Use the HBOM's structural relationships to support impact analysis, enabling rapid identification of affected assemblies when a specific component is implicated in a risk.
Scope the HBOM's purpose clearly, recognizing that it primarily supports component traceability and does not by itself cover financial, operational, geopolitical, or ESG risk of the suppliers involved.
Promotional banner for the Penetration Report Template Kit