---
id: wiki-2026-0508-sca-fundamentals
title: SCA Fundamentals (Software Composition Analysis)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Software Composition Analysis, Dependency Scanning, OSS Security]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [sca, security, devsecops, sbom, supply-chain]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: Multi
  framework: Snyk / Dependabot / Trivy / Grype
---

# SCA Fundamentals (Software Composition Analysis)

## 매 한 줄
> **"매 third-party (OSS) dependency 의 vuln/license/integrity scan — 매 modern app 의 80%+ 가 OSS 코드라는 현실 위의 baseline 통제"**. 매 Heartbleed (2014), Equifax/Struts (2017), Log4Shell (2021), xz-utils backdoor (2024) 가 매 SBOM + SCA 를 매 NIST/EU CRA/US EO 14028 의 의무 사항 으로 격상. 매 2026 supply chain 공격 시대의 first line of defense.

## 매 핵심

### 매 What SCA scans
- **Direct deps**: package.json, requirements.txt, go.mod, Cargo.toml.
- **Transitive deps**: full dependency tree (often 10x direct).
- **Container images**: OS packages + app deps (Trivy, Grype).
- **License**: GPL/AGPL/proprietary compliance.
- **Integrity**: signature, provenance (Sigstore, SLSA).

### 매 Vulnerability sources
- **NVD/CVE**: NIST National Vulnerability Database.
- **GitHub Advisory Database (GHSA)**: ecosystem-aware.
- **OSV.dev**: Google distributed vuln DB.
- **Vendor advisories**: Snyk DB, Mend, Sonatype OSS Index.
- **EPSS**: Exploit Prediction Scoring System (probabilistic priority).

### 매 SBOM formats
- **SPDX**: ISO/IEC 5962, Linux Foundation.
- **CycloneDX**: OWASP, security-focused, VEX support.
- **VEX** (Vulnerability Exploitability eXchange): "vulnerable but not exploitable in our config".

### 매 응용
1. PR-time scanning (Dependabot, Snyk PR check).
2. Container scan in CI (Trivy in GitHub Actions).
3. SBOM generation for compliance (EU CRA, US EO).
4. Runtime correlation (Sysdig, Wiz — used vs unused vulns).
5. License audit before release.

## 💻 패턴

### npm audit + fix in CI
```bash
npm audit --audit-level=high --json > audit.json
# Auto-fix non-breaking
npm audit fix
# Force breaking fix only on dev branches
npm audit fix --force
```

### Trivy container scan (GitHub Actions)
```yaml
- name: Run Trivy
  uses: aquasecurity/trivy-action@master
  with:
    image-ref: 'ghcr.io/org/app:${{ github.sha }}'
    format: 'sarif'
    output: 'trivy.sarif'
    severity: 'CRITICAL,HIGH'
    exit-code: '1'
    ignore-unfixed: true
- uses: github/codeql-action/upload-sarif@v3
  with: { sarif_file: 'trivy.sarif' }
```

### CycloneDX SBOM (Python)
```bash
pip install cyclonedx-bom
cyclonedx-py requirements -i requirements.txt -o sbom.json --format json
# Validate
cyclonedx validate --input-file sbom.json
```

### Dependabot config (GitHub)
```yaml
# .github/dependabot.yml
version: 2
updates:
  - package-ecosystem: "npm"
    directory: "/"
    schedule: { interval: "weekly" }
    open-pull-requests-limit: 10
    groups:
      minor-and-patch:
        update-types: ["minor", "patch"]
  - package-ecosystem: "docker"
    directory: "/"
    schedule: { interval: "daily" }
```

### EPSS-based prioritization
```python
import requests

def epss_score(cve_id):
    r = requests.get(f"https://api.first.org/data/v1/epss?cve={cve_id}").json()
    if r["data"]:
        return float(r["data"][0]["epss"]), float(r["data"][0]["percentile"])
    return None, None

# Prioritize: high CVSS AND high EPSS (likely exploited in wild)
for cve in scan_results:
    epss, pct = epss_score(cve.id)
    if cve.cvss >= 7.0 and epss and epss > 0.5:
        page_oncall(cve)
```

### Sigstore cosign verification (provenance)
```bash
# Verify image was built by trusted GitHub Actions workflow
cosign verify ghcr.io/org/app:v1.2.3 \
  --certificate-identity "https://github.com/org/repo/.github/workflows/release.yml@refs/tags/v1.2.3" \
  --certificate-oidc-issuer "https://token.actions.githubusercontent.com"
```

### VEX statement (CycloneDX)
```json
{
  "vulnerabilities": [{
    "id": "CVE-2024-XXXX",
    "ratings": [{"severity": "critical"}],
    "analysis": {
      "state": "not_affected",
      "justification": "code_not_reachable",
      "detail": "Vulnerable function in lib X is never called; entrypoint disabled."
    }
  }]
}
```

### Grype with custom policy
```bash
grype dir:./app -o sarif --fail-on high \
  --only-fixed \
  --exclude './vendor/**'
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Open source project | Dependabot (free, GitHub-native) |
| Polyglot enterprise | Snyk / Mend / Sonatype Lifecycle |
| Container-heavy | Trivy / Grype + admission controller |
| Air-gapped | Self-hosted DB (Anchore Enterprise, Trivy with local DB) |
| Compliance (EU CRA, FedRAMP) | SBOM + VEX + signed attestations (SLSA L3+) |

**기본값**: Trivy in CI + Dependabot for upgrades + CycloneDX SBOM + Sigstore signing.

## 🔗 Graph
- 부모: [[DevSecOps]] · [[Application-Security]]
- 변형: [[SAST]] · [[DAST]] · [[Container-Scanning]]
- 응용: [[SBOM]] · [[License-Compliance]] · [[Vulnerability-Management]]
- Adjacent: [[Supply-Chain-Security]] · [[SLSA]] · [[Sigstore]]

## 🤖 LLM 활용
**언제**: triaging vuln noise (false positive vs real), generating VEX justifications from code context, summarizing CVE for stakeholders, suggesting upgrade paths.
**언제 X**: as the source of truth for vuln data — use NVD/OSV/GHSA. LLM only for prioritization and explanation.

## ❌ 안티패턴
- **Scan once, ship**: vulns appear post-release; need continuous monitoring.
- **Block on every CVE**: dev fatigue → bypass culture; use EPSS + reachability.
- **No transitive scan**: direct deps look clean while transitive has critical CVE.
- **SBOM but no VEX**: dump 10k vulns on customers without exploitability context.
- **Ignore lockfiles**: scan only manifest → miss pinned vulnerable transitive.

## 🧪 검증 / 중복
- Verified (NIST SP 800-218 SSDF, CISA SBOM guidance, OWASP Dependency-Track).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — SCA, SBOM, EPSS, VEX, Sigstore patterns |
