No software projects can do without components. Software libraries are the most common ingredient. Some programming languages use the concept of modules or plugins. Then there are frameworks typically used in web applications. All of these parts can feature different versions, because some requirement fixed the version to a major release. If one component exhibits a security vulnerability, then the code in question must be updated. Given the size of modern applications, this can be a challenge. Remember the Log4j vulnerability from last year. Many teams didn’t even know that they were running applications containing Log4j. Attackers know about this and target the supply chain of the code. Finding a critical bug in components can open up a wide variety of code for attacks. This is where the Software Bill of Materials (SBOM) comes into play.
SBOM is simply a list of components that your applications contains. Most teams using build tools have this already implicitly. Basically, SBOM is a standard for the manifest of components your software brings with it. The National Telecommunications and Information Administration (NTIA) has compiled a set of resources describing how to use the standard. The idea is not new. There already exists Software Package Data Exchange® (SPDX®), OWASP CycloneDX, and ISO/IEC 19770-2:2015. Everything boils down to a specification for a JSON document that contains all relevant metadata of all components. The key is to catch all the dependencies. Some libraries depend on others, so package managers can resolve these links and install additional components. Build systems do this automatically, but the SBOM needs to be complete. Another problem is the categorisation. Some parts of the code belong to the runtime, some are managed by the operating system, and others are shipped within the application itself. A full SBOM needs to combine these sources. Your toolchain can help you there. C/C++ compiler can create a list of all headers used during compilation (the Clang/GCC flags -MD and -MF name.out.d take care of it). This is just a part of the development environment. You have to create a manifest for container images and other deployment methods as well. Be as accurate as possible, and make sure that SBOM creating is an automated part of your build pipeline.