# SRI uses SHA-384 or stronger

- **Pattern:** `ab-002429` (`security-headers-ii.supply-chain.sri-strong-hash`)
- **Severity:** medium
- **Lifecycle:** active
- **Last modified:** 2026-04-18
- **Canonical URL:** https://auditbuffet.com/patterns/ab-002429
- **License:** CC-BY-4.0 — attribute to AuditBuffet Pattern Catalog (https://auditbuffet.com/patterns/ab-002429)

## Why it matters

Subresource Integrity hashes cryptographically verify that a resource loaded from a CDN has not been tampered with. SHA-256 is technically valid but weaker than the W3C-recommended minimum of SHA-384 — collision attacks on SHA-256 are within the theoretical reach of well-resourced adversaries, and the W3C explicitly recommends SHA-384 for SRI. CWE-345 (Insufficient Verification of Data Authenticity) and CWE-494 (Download of Code Without Integrity Check) both apply when hash strength is below recommended minimums. OWASP A08 (Software and Data Integrity Failures) flags weak or absent integrity verification as a supply chain risk.

## Severity rationale

Medium because SHA-256-only SRI hashes are technically valid but below the W3C recommended strength floor, creating a marginal but unnecessary gap in supply chain integrity verification.

## Remediation

Upgrade all SRI hashes from SHA-256 to SHA-384. Regenerate hashes using OpenSSL or a trusted SRI hash generator.

```html
<!-- Before: SHA-256 only (below W3C recommended minimum) -->
<script src="https://cdn.example.com/lib.js"
  integrity="sha256-abc123..."
  crossorigin="anonymous"></script>

<!-- After: SHA-384 (W3C recommended minimum) -->
<script src="https://cdn.example.com/lib.js"
  integrity="sha384-xyz789..."
  crossorigin="anonymous"></script>
```

Generate SHA-384 hashes: `openssl dgst -sha384 -binary lib.js | openssl base64 -A`. You can also specify both algorithms (`sha384-... sha512-...`) for belt-and-suspenders verification — the browser uses the strongest supported hash.

## Detection

- **ID:** `sri-strong-hash`
- **Severity:** `medium`
- **What to look for:** Search all HTML templates, page components, and layout files for elements with `integrity` attributes. For each, parse the hash algorithm prefix. SHA-384 is the W3C recommended minimum — SHA-256 is technically valid but weaker. Count all SRI integrity attributes and their hash strengths.
- **Pass criteria:** 100% of SRI hashes use SHA-384 or SHA-512. Report: "X of Y SRI hashes use SHA-384+."
- **Fail criteria:** Any SRI integrity attribute uses only SHA-256 without SHA-384 or SHA-512.
- **Skip (N/A) when:** No external scripts or stylesheets loaded — all resources are first-party or bundled.
- **Detail on fail:** `"X of Y SRI hashes use only SHA-256 — SHA-384 is the W3C recommended minimum"` or `"External stylesheet integrity uses sha256 only — upgrade to sha384"`
- **Remediation:** Upgrade SRI hashes from SHA-256 to SHA-384 (the W3C recommended minimum):

  ```html
  <!-- Before: SHA-256 only -->
  <script src="https://cdn.example.com/lib.js"
    integrity="sha256-abc123..."
    crossorigin="anonymous"></script>

  <!-- After: SHA-384 (recommended) -->
  <script src="https://cdn.example.com/lib.js"
    integrity="sha384-xyz789..."
    crossorigin="anonymous"></script>
  ```

  Generate SHA-384 hashes: `openssl dgst -sha384 -binary lib.js | openssl base64 -A`

## External references

- cwe CWE-345
- cwe CWE-494
- owasp A08

Taxons: supply-chain, cryptography-and-secrets

HTML version: https://auditbuffet.com/patterns/ab-002429