# CVSS v4.0 Receipts – Hardening Guide

Source advisory: `docs/product-advisories/25-Nov-2025 - Add CVSS v4.0 Score Receipts for Transparency.md` (CV1–CV10). This guide turns the gaps into implementable rules for Sprint 0190.

## Canonical hashing (CV2)
- Serializer: JSON Canonicalization Scheme (JCS).
- Ordering: lexicographic keys; arrays keep order; drop nulls.
- Numbers: fixed 4-decimal precision; invariant culture; no exponent.
- Time: UTC ISO-8601 `Z`; strip milliseconds unless non-zero.
- Hash: SHA-256 of canonical JSON; store as `inputsHash` and DSSE subject.
- Test vectors: `tests/Policy/StellaOps.Policy.Scoring.Tests/Fixtures/hashing/` (`receipt-input.json` + `receipt-input.sha256`).
- Recompute locally:
  ```bash
  python - <<'PY'
  import json, hashlib, pathlib
  data=json.loads(pathlib.Path('tests/Policy/StellaOps.Policy.Scoring.Tests/Fixtures/hashing/receipt-input.json').read_text())
  canon=json.dumps(data, sort_keys=True, separators=(',', ':'), ensure_ascii=False)
  print(hashlib.sha256(canon.encode()).hexdigest())
  PY
  ```

## Policy replay & backfill (CV1)
- Policies immutable; bump version for any change.
- On change, emit new receipts with `supersedesReceiptId` and retain old ones.
- Backfill job: re-score under new policy, append history, re-sign DSSE.

## Tenant segregation & RBAC (CV4, CV9)
- Storage keys include `tenantId`; hashes/DSSE annotate tenant.
- Roles: Security Engineer (Base), SOC Analyst (Threat), Customer Admin (Env), Viewer (read-only).
- Enforce at API/repo layer and in canonical hash.

## Deterministic exports (CV8)
- JSON export: JCS ordering, UTF-8, UTC timestamps, stable severity palette.
- PDF export: embed fonts (Source Sans 3 + Roboto Mono), A4, fixed margins; hash PDF bytes and persist `exportHash`.
- Offline receipt bundle: include JSON, PDF, DSSE envelope, and policy hash; tar with sorted names + fixed mtime.

## v3.1 → v4.0 conversion (CV5)
- Deterministic mapping; tag `source: "converted-v3.1"`, set `conversionMethod` + `confidence`; retain vendor vector.
- Record `conversionHash` of the original v3.1 vector (JCS + SHA-256) and store in receipt history for audit.

## Evidence provenance (CV6)
- Evidence items use CAS URIs + DSSE refs, include `retentionClass`, `redactionStatus`, `verifiedAt`, `hashMismatch`.
- Receipt schema enforces evidence array; DSSE subject hash must match `inputsHash`.

## Immutability & monitoring (CV7, CV10)
- Receipts append-only; amendments create new IDs + DSSE.
- Alerts: DSSE verify failures, policy hash drift, hash mismatch, engine version skew. Prometheus counters: `cvss_receipt_dsse_failures_total`, `cvss_policy_drift_total`, `cvss_hash_mismatch_total`.
- Receipt history includes `supersedesReceiptId` and `amendsReceiptId`; policy backfill job must set `supersedesReceiptId` when replaying.
- Dashboard SLO: DSSE failure rate <0.1% per 24h; policy drift alerts page security on-call.

## Golden fixtures & locations
- Hashing vectors: `tests/Policy/StellaOps.Policy.Scoring.Tests/Fixtures/hashing/receipt-input.json` with expected hash `receipt-input.sha256`.
- Receipt DSSE/PDF examples to live under `tests/Policy/StellaOps.Policy.Scoring.Tests/Fixtures/receipts/` as exports land.
- Sample PDFs in `Fixtures/exports/` once generated; hash each to `*.pdf.sha256`.

## Implementation checklist
- Wire `ReceiptCanonicalizer` to JCS rules above.
- Add backfill job + history persistence.
- Enforce tenant/RBAC and annotate hashes/DSSE.
- Implement deterministic PDF export and record `exportHash`.
- Store conversion metadata for v3.1 sources.
- Verify evidence CAS/DSSE on ingest; fail closed.
- Expose metrics/alerts listed above.

## Receipt model (API shape)
- `receiptId`, `schemaVersion`, `format`, `vulnerabilityId`, `tenantId`, `createdAt/by`, `modifiedAt/by`.
- Metric inputs: `baseMetrics`, optional `threatMetrics` and `environmentalMetrics`, optional `supplementalMetrics`.
- Computed outputs: `scores` (base/threat/environmental/full plus `effectiveScore` and `effectiveScoreType`), `vectorString`, `severity`.
- Policy link: `policyRef { policyId, version, hash, activatedAt }` plus `inputHash` (JCS + SHA-256) and optional `exportHash`.
- Evidence: `evidence[]` (type, uri, description, source, collectedAt, dsseRef, isAuthoritative, isRedacted, verifiedAt, retentionClass).
- Attestation + history: `attestationRefs[]` (DSSE envelopes), `history[]` (field, previousValue, newValue, actor, reason, referenceUri, when), `amendsReceiptId`, `supersedesReceiptId`, `isActive`.

## Gateway API (Policy Engine via Gateway)
- Base path: `/api/cvss` (Policy Gateway). Scopes: `policy.run` for create/amend; `findings.read` for read/history/policies.
- Endpoints:
  - `POST /api/cvss/receipts` – Create a receipt and optional DSSE envelope.
  - `GET /api/cvss/receipts/{id}` – Fetch the latest receipt with scores, evidence, and hashes.
  - `PUT /api/cvss/receipts/{id}/amend` – Append a history entry (e.g., policy change, evidence fix); re-sign when `signingKey` is provided.
  - `GET /api/cvss/receipts/{id}/history` – Return ordered history entries for the receipt.
  - `GET /api/cvss/policies` – List available `CvssPolicy` documents (id/version/hash/effective window).

**Create receipt (minimal example)**

```
POST /api/cvss/receipts
Authorization: Bearer <token>
Content-Type: application/json

{
  "vulnerabilityId": "CVE-2025-1234",
  "policy": {
    "policyId": "default",
    "version": "1.0.0",
    "name": "Default CVSS policy",
    "effectiveFrom": "2025-12-01T00:00:00Z",
    "hash": "sha256:..."
  },
  "baseMetrics": { "av": "Network", "ac": "Low", "at": "None", "pr": "None", "ui": "None", "vc": "High", "vi": "High", "va": "High", "sc": "High", "si": "High", "sa": "High" },
  "environmentalMetrics": { "cr": "High", "ir": "High", "ar": "Medium" },
  "signingKey": { "keyId": "cvss-dev", "store": "local" },
  "createdBy": "cli"
}
```

**Response 200 (abridged)**

```json
{
  "receiptId": "cvss-20251207-01",
  "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/CR:H/IR:H/AR:M",
  "scores": { "baseScore": 9.3, "threatScore": 9.3, "environmentalScore": 9.1, "fullScore": 9.1, "effectiveScore": 9.1, "effectiveScoreType": "Environmental" },
  "severity": "Critical",
  "policyRef": { "policyId": "default", "version": "1.0.0", "hash": "sha256:..." },
  "inputHash": "sha256:...",
  "attestationRefs": ["dsse:stella.ops/cvssReceipt@v1/sha256:..."],
  "evidence": [],
  "history": []
}
```

## CLI and UI usage
- CLI (`stella cvss ...` via `src/Cli/StellaOps.Cli`):
  - `stella cvss score --vuln CVE-2025-1234 --policy-file cvss-policy.json --vector CVSS:4.0/AV:N/... [--json]`
  - `stella cvss show <receiptId> [--json]`
  - `stella cvss history <receiptId> [--json]`
  - `stella cvss export <receiptId> --format json --out cvss-receipt.json`
  - Uses Policy Gateway `/api/cvss/...` endpoints, enforces tenant scoping via `--tenant`/profile, and reuses `CvssV4Engine` locally for vector parsing.
- Console (`src/Web/StellaOps.Web`):
  - Route `/cvss/receipts/:receiptId` renders a receipt viewer with score badge, vector summary, and tabs for Base/Threat/Environmental/Evidence/Policy/History.
  - Export and "Recalculate with my env" flows reuse the same receipt payload; UI expects deterministic ordering and stable hashes.