# Tool design ## Concepts sbom-cve-check tool is composed of 3 types of concept: - [Database](database.md) - [SBOM](sbom.md) - [Export](export.md) For each concept, [plugins](plugins.md) can be registered to add custom functionalities. ### CVE database A {term}`CVE database` contains {term}`CVE` entries. An {term}`annotation` entry is a special kind of CVE entry, which is contained in an {term}`Annotation database`. Each database class is automatically registered into a registry, thanks to the `@register_vuln_db('...')` decorator. The `register_vuln_db` function parameter is the type name to register. The list of builtins CVE database type names is provided in the [CVE database](database.md#database-type) section. In the diagram below, the class diagram associated with CVE databases. :::{note} Not all class are listed, only the most important ones. ::: ```mermaid classDiagram class VulnDatabase class GitVulnDatabase VulnDatabase <|-- GitVulnDatabase class CveListVulnEntry class CveListVulnDatabase GitVulnDatabase <|-- CveListVulnDatabase CveListVulnDatabase o-- CveListVulnEntry class NvdVulnEntry class NvdFkieVulnDatabase GitVulnDatabase <|-- NvdFkieVulnDatabase NvdFkieVulnDatabase o-- NvdVulnEntry class AnnotDatabase VulnDatabase <|-- AnnotDatabase class GitAnnotDatabase AnnotDatabase <|-- GitAnnotDatabase class OpenVexAnnotEntry class OpenVexAnnotDatabase GitAnnotDatabase <|-- OpenVexAnnotDatabase OpenVexAnnotDatabase o-- OpenVexAnnotEntry class Spdx3AnnotEntry class Spdx3AnnotDatabase AnnotDatabase <|-- Spdx3AnnotDatabase Spdx3AnnotDatabase o-- Spdx3AnnotEntry class YoctoAnnotEntry class YoctoAnnotDatabase AnnotDatabase <|-- YoctoAnnotDatabase YoctoAnnotDatabase o-- YoctoAnnotEntry class VulnDbEntry VulnDbEntry <|-- CveListVulnEntry VulnDbEntry <|-- NvdVulnEntry class AnnotDbEntry VulnDbEntry <|-- AnnotDbEntry AnnotDbEntry <|-- OpenVexAnnotEntry AnnotDbEntry <|-- Spdx3AnnotEntry AnnotDbEntry <|-- YoctoAnnotEntry class GitDatabase GitVulnDatabase o-- GitDatabase GitAnnotDatabase o-- GitDatabase ``` To speed up the lookup of CVEs that are associated with a component, the various databases are indexed: For each database, an index is created, which is a map between CPE product name (and only that part) and the list of potentially associated CVE identifiers. For git databases, `GitVulnDatabase` or `GitAnnotDatabase`, the index of the database is stored to disk at the root of the git tree with the following name: `.sbom-cve-check-cache-index.json`. The index is stored to disk because indexing the database takes a bit of time. To invalidate the cache file, it contains the associated commit hash identifier and the hash of relevant configuration values. The various database indexes are merged into a unique index stored in RAM. The logic to obtain the applicable CVEs for a {term}`component` identifier is described in the [section below](#find-applicable-cve). ### SBOM A {term}`SBOM` provides, among other things, the components contained in the image deployed to the device. Each SBOM class is automatically registered into a registry, thanks to the `@register_sbom('...')` decorator. The `register_sbom` function parameter is the type name to register. The list of SBOM builtins type names is provided in the [SBOM supported formats](sbom.md#supported-formats) section. In the diagram below, the class diagram associated with SBOM: ```mermaid classDiagram class Sbom { +Component components +components_grouped_by_id() +write_to_file() } class Component { +name +version +identifiers +description +compiled_sources } class Spdx3Sbom class Spdx3Component Sbom <|-- Spdx3Sbom Sbom o-- Component Spdx3Sbom o-- Spdx3Component ``` ### Export The tool provides multiple kinds of export types. The list of builtins export type names is provided in the [export formats](export.md#export-formats) section. Each export class is automatically registered into a registry, thanks to the `@register_export('...')` decorator. The `register_export` function parameter is the type name to register. In the diagram below, the class diagram associated with export types: ```mermaid classDiagram class BaseExport { +process_export() -_is_vuln_filtered() } class CsvExport class Spdx3Export class YoctoCveCheckExport BaseExport <|-- CsvExport BaseExport <|-- Spdx3Export BaseExport <|-- YoctoCveCheckExport ``` From the `process_export()` function: - From the [SBOM](#sbom) the list of build "recipe" is retrieved, thanks to `iterate_component_builds()`. This function returns `CompBuild` objects, each containing one or multiple components with the same vendor and product name, and with the same version. Typically, there are multiple components with the same identifier when a package is split into sub-packages. - Then, for each group of components with the same identifier and the same version, a search for applicable CVE is realized as described in the [subsection below](#find-applicable-cve). Here, the term "applicable" means that the CVE is associated with this component identifier regardless of the component version. - For each found CVE identifier, a special annotation object is created, named `AggregateAnnotEntry`. This object aggregates the various sources of information from the CVE databases that were registered. This object is also responsible for computing the [VEX assessment](#compute-vex-assessment), as described in the subsection below, associated with the previously mentioned group of components. - The `_is_vuln_filtered()` method of the `BaseExport` class allows to filter (exclude) annotations that will be exported. The various filters are described in the [export options](export.md#export-options). ## Find applicable CVE In this section, the term "applicable" means that the CVE is associated with this component identifier regardless of the component version. It does not mean that the component is vulnerable. To find applicable CVE, from one or more component identifiers, obtained, for example, from a CPE, the following strategy is realized: - First get a unique list of product names and group component identifiers by product name. - For each product name, the database index, which is described in the [CVE database](#cve-database) subsection, is queried to obtain a unique set of potential associated CVEs. Some CVEs in this list may not be applicable, since we only looked for the product name, without checking for the vendor part of the CPE. - In some databases, for the same CVE identifier, the information used to identify the component is sometimes incomplete; for example, the vendor part may be missing, but another database may have all the information needed to confirm, without a doubt, whether the component is applicable. To be able to confirm that the CVE is applicable (or not), the following algorithm is used (for each CVE): - For each component product name, get the component identifiers (from CPE) specified in CVEs that loosely match, which means that they have the same product name without checking for other fields (vendor, ...). - Still for each component product name, keep only the best associated CVE component identifiers: If there are CVE component identifiers with the vendor part, only keep those, otherwise take all the identifiers found. - Then check if one of the component identifiers fully matches with the CVE component identifiers that were kept. If there is a match, consider that this CVE identifier is applicable to the component to check. ## Compute VEX assessment To compute the CVE VEX assessment associated with one or more component identifiers and one version, the following algorithm is used. - Retrieve the CVE database entries associated with the CVE identifier to check, and group these entries by priority: - For CVE database entries, which are annotations, check that the component version is exactly the same as one of the versions specified in the annotation. If there is no match, do not use this CVE entry (annotation). - For CVE database entries, which are not annotations (typically an entry from NVD or CVE List CVE database), always take all entries. - First, regardless of the database priority, if any CVE database entry indicates that the vulnerability is rejected, indicate that the component is not affected, and provide this assessment. - For each group of CVE database entries, which were grouped by priority, execute the following checks, starting with the group with the highest priority: - If the CVE database entry is an annotation, take the VEX assessment provided by this annotation if there is any. - Otherwise, "merge" the CVE database entries: retrieve all the version ranges applicable to the component. From these version ranges compute the VEX assessment, which is described in more detail in the [subsection below]( #compute-vex-assessment-from-semantic-version-ranges). - For this current database priority, if no assessment was computed or if the component is considered vulnerable, check if affected sources by the vulnerability are compiled, which is described in more detail in the [subsection below](#compute-vex-assessment-from-compiled-sources). - If no assessment could be computed, repeat this process with CVE database entries with lower priority. In the end if no assessment could be computed, generate a default assessment indicating that databases do not contain enough version information. This default assessment considers that the component is affected (vulnerable) by this CVE. :::{note} To simplify this explanation, the computation of obsolete assessments was ignored. ::: ### Compute VEX assessment from semantic version ranges From the group of CVE database entries with the same priority, retrieve the list of version ranges applicable to the component being assessed. Each version range may indicate either a range of vulnerable versions or a range of unaffected versions. Currently, the version ranges are retrieved from the following sources: - From NVD database, the ranges are retrieved from `configurations` → `nodes` → `cpeMatch`, if the CPE is applicable to the component being assessed. - From CVE List database, from all the containers (CNA, or ADP), the version ranges are retrieved: - From `cpeApplicability` → `nodes` → `cpeMatch`, if the CPE is applicable to the component being assessed. - From `affected` → `versions`, if the version range is considered applicable to the component being assessed: - If one of `affected` → `cpes` matches the component being assessed, - Or, if the `affected` → `packageName` matches the component being assessed, - Or, if both fields (`cpes` and `packageName`) are missing, and there is only one vulnerable CPE provided by `cpeApplicability` → `nodes` → `cpeMatch` matching the component being assessed. Then, the component version is compared against the list of version ranges that was retrieved. For each version range: - If this is a vulnerable version range, check if the component version is within the range, smaller or greater. - If this is an unaffected version range, check if the component version is within the range or outside this range. And finally, the VEX assessment is computed using the following rules: - If the component version is within an unaffected version range, and if this range was provided by the kernel.org CNA, then indicate that the vulnerability is fixed with the following status notes: `version-not-in-range`. - If the component version is within a vulnerable version range, then indicate that the vulnerability is affecting this component with the following status notes: `version-in-range`. - If the component version is only outside an unaffected version range (it is not inside an unaffected version range, and it is not outside a vulnerable version range), then indicate that the vulnerability is affecting this component with the following status notes: `version-maybe-in-range`. - If the component version is outside a vulnerable version range, or it is inside an unaffected version range, then indicate that the vulnerability is fixed with the following status notes: `version-not-in-range`. - Otherwise, if there was no version range found, do not provide a VEX assessment (at this point). ### Compute VEX assessment from compiled sources If the vulnerability database entry (typically from CVE List database) provides a list of affected sources (program files), and if the SBOM provides compiled source files for this component, check if we can ignore this vulnerability. If both conditions are not met, do not provide any assessment. For each listed affected source file, check if the affected file path is a "suffix" of one of the listed compiled file paths. This is done this way, since most of the time the compiled file path is prefixed with the build directory. If all affected source files are not found in the list of compiled files, then indicate that the component is not affected with the following justification: "vulnerable code not present". Otherwise, do not provide any assessment.