@mitre/hdf-extension-graph

@mitre/hdf-extension-graph

Bidirectional extension graph processing for HDF baseline hierarchies.

Why this exists

HDF baseline documents can represent 'overlay' structures that form extension chains of parent baselines and their children. For example, a DISA STIG baseline defines hundreds of requirements; an organizational overlay on that DISA baseline can modify a subset for organization-specific policies; a project overlay can further tighten thresholds for a specific system. When an HDF results file contains multiple baselines linked via parentBaseline, understanding what each layer changed requires walking these chains bidirectionally.

Without this library, answering "did this overlay change the impact of SV-238196, or inherit it unchanged?" requires manually cross-referencing requirements across baselines by ID. The extension graph provides:

• root — jump from any overlay requirement to the original base definition
• modifications — which fields (impact, title, severity, effectiveImpact, disposition) an overlay changed relative to its parent
• isRedundant — whether an overlay re-declares a control without actually changing it
• fullCode — the complete code from all layers in one string
• extensionChain — the ordered list of baselines from root to leaf

This is the same graph algorithm that powers Heimdall's control detail panel, extracted as a standalone library.

Installation

pnpm add @mitre/hdf-extension-graph

Requires @mitre/hdf-schema as a peer dependency.

Usage

Build the graph

import { buildExtensionGraph } from '@mitre/hdf-extension-graph';
import type { HDFResults } from '@mitre/hdf-schema';

const hdfResults: HDFResults = JSON.parse(fileContents);
const graph = buildExtensionGraph(hdfResults);

Navigate baselines

// Find root baselines (no parent)
const roots = graph.rootBaselines;

// Find a specific baseline
const stig = graph.findBaseline('rhel9-stig-baseline');

// See what extends it
for (const overlay of stig.extendedBy) {
  console.log(`${overlay.data.name} extends ${stig.data.name}`);
}

Navigate requirements

// Find all instances of a control across all baselines
const controls = graph.findRequirements('SV-238196');

// Get the root (base) control
const root = controls[1].root; // walks up the chain

// Get the full code with all layers
console.log(controls[1].fullCode);
// # my-overlay
// describe sshd_config do
//   its("ClientAliveInterval") { should cmp <= 300 }
// end
//
// # rhel9-stig-baseline
// describe sshd_config do
//   its("ClientAliveInterval") { should cmp <= 600 }
// end

Detect changes

const overlay = graph.baselines[1].requirements[0];

// Is this overlay just inheriting, or did it change something?
if (!overlay.isRedundant) {
  console.log('This overlay modifies the base control');
}

// What specifically changed?
for (const mod of overlay.modifications) {
  console.log(`${mod.field}: ${mod.originalValue} → ${mod.newValue}`);
}
// impact: 0.5 → 0.9
// title: SSH timeout → SSH timeout (project)

Walk the chain

// Ordered list of baselines from root to current
const chain = overlay.extensionChain;
console.log(chain.map(b => b.data.name));
// ['disa-rhel7-stig', 'cms-rhel7-overlay', 'project-overlay']

API

buildExtensionGraph(results: HDFResults): ExtensionGraph

Builds a bidirectional extension graph from an HDF Results file. Links baselines via parentBaseline and requirements by matching id across linked baselines.

ExtensionGraph

Property / Method	Type	Description
baselines	ContextualizedBaseline[]	All baselines in the graph
requirements	ContextualizedRequirement[]	All requirements across all baselines
rootBaselines	ContextualizedBaseline[]	Baselines with no parent
findBaseline(name)	ContextualizedBaseline | undefined	Find baseline by name
findRequirements(id)	ContextualizedRequirement[]	Find all requirements with given id

ContextualizedBaseline

Property	Type	Description
data	EvaluatedBaseline	Original baseline data
sourcedFrom	HDFResults	The results file this came from
extendsFrom	ContextualizedBaseline[]	Parent baselines
extendedBy	ContextualizedBaseline[]	Child baselines
requirements	ContextualizedRequirement[]	Wrapped requirements

ContextualizedRequirement

Property	Type	Description
data	EvaluatedRequirement	Original requirement data
sourcedFrom	ContextualizedBaseline	Owning baseline
extendsFrom	ContextualizedRequirement[]	Parent requirements
extendedBy	ContextualizedRequirement[]	Child requirements
root	ContextualizedRequirement	Base requirement at bottom of chain
isRedundant	boolean	True if code is empty or matches root
fullCode	string	Concatenated code from all layers
extensionChain	ContextualizedBaseline[]	Baselines from root to leaf
modifications	Modification[]	Fields changed vs immediate parent

Modification

interface Modification {
  field: string;        // 'impact', 'title', or 'severity'
  originalValue: unknown;
  newValue: unknown;
  inBaseline: string;   // Name of the baseline making the change
}

Notes

• TypeScript only — there is no Go implementation of hdf-extension-graph.
• The HDF schemas consumed by this package are documented at https://mitre.github.io/hdf-libs/schemas/.

License

Apache-2.0