ring:dev-docker-security

Docker Security — Docker Hub Health Score Grade A

Overview

General Dockerfile patterns are documented in dev-team/docs/standards/devops.md#containers. This skill focuses specifically on Docker Hub Health Score compliance.

This skill creates or audits Dockerfiles and image configurations to achieve Docker Hub Health Score grade A.

Docker Hub Health Score Policies

#	Policy	Weight	How to Comply
1	Default non-root user	Required	Dockerfile MUST have a USER directive with a non-root user
2	No fixable critical/high CVEs	Required	Zero critical/high vulnerabilities with available fixes
3	No high-profile vulnerabilities	Required	Zero CVEs in the CISA KEV catalog
4	No AGPL v3 licenses	Required	No packages with AGPL-3.0 licenses
5	Supply chain attestations	Required	SBOM + provenance attached to pushed images (pipeline config)
6	No outdated base images	Optional	Only evaluated for Docker Hub hosted base images
7	No unapproved base images	Optional	Only evaluated for Docker Hub hosted base images

Policies 6 and 7 are optional — not evaluated when using non-Docker Hub base images (e.g., gcr.io/distroless). Do not treat them as blockers.

---

Pipeline Enforcement

These policies are automatically enforced on every PR that changes application components. The PR Security Scan workflow blocks merge if any required policy fails.

What happens on every PR

1. Docker image is built from the Dockerfile in the PR
2. Trivy scans the image for vulnerabilities and AGPL-3.0 licenses
3. Dockerfile analysis verifies the USER directive
4. CISA KEV cross-reference checks found CVEs against the Known Exploited Vulnerabilities catalog
5. Health Score Compliance table is posted as a PR comment

Merge gate

Any policy failure blocks the PR — missing USER directive, a fixable critical/high CVE, a KEV vulnerability, or an AGPL-3.0 package.

Policy 5 (SBOM + provenance) is evaluated only on release builds via pipeline config:

sbom: generator=docker/scout-sbom-indexer:latest
provenance: mode=max

---

Step 1: Analyze Current State

1. Read the Dockerfile (if mode=audit)
2. Identify: base image, build stages, USER directive, package installation
3. If mode=create, gather requirements from inputs

Step 2: Apply Security Policies

Policy 1 — Default Non-Root User

Every Dockerfile MUST set a non-root user after all RUN/COPY steps:

USER nonroot:nonroot          # distroless (pre-existing user)

# Alpine: create user first
RUN addgroup -S appgroup && adduser -S appuser -G appgroup
USER appuser

# Debian/Ubuntu: create user first
RUN groupadd -r appgroup && useradd -r -g appgroup appuser
USER appuser

USER root does NOT satisfy this policy. The user must be non-root and must exist in the image.

Policies 2 & 3 — No Fixable CVEs / No KEV Vulnerabilities

Both policies share the same remediation — minimize the attack surface:

• Prefer distroless — ~0 CVEs (no shell, no package manager)
• Alpine over Debian/Ubuntu — fewer packages = fewer CVEs
• Multi-stage builds — build tools stay in builder, only runtime in final
• Pin versions — avoid pulling newly vulnerable packages
• Update base images regularly

FROM gcr.io/distroless/static-debian12    # Go (statically compiled)
FROM gcr.io/distroless/base-debian12      # Dynamically linked
FROM node:22-alpine                        # Node.js

Policy 4 — No AGPL v3 Licenses

Audit dependencies before adding them. Use trivy fs --scanners license to check. If AGPL-3.0 is found, replace the dependency. This applies to ALL packages in the final image, including OS packages.

Policy 5 — Supply Chain Attestations

Not a Dockerfile concern — configured in the build pipeline (sbom: + provenance: mode=max). When auditing, verify the CI/CD pipeline includes both parameters.

---

Step 3: Dockerfile Templates

Go Service

FROM golang:1.24-alpine AS builder
RUN apk add --no-cache ca-certificates tzdata
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 \
    go build -ldflags="-s -w" -o /app/server ./cmd/app

FROM gcr.io/distroless/static-debian12
COPY --from=builder /app/server /server
EXPOSE 8080
USER nonroot:nonroot
ENTRYPOINT ["/server"]

Node.js Service

FROM node:22-alpine AS builder
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci --only=production
COPY . .
RUN npm run build

FROM node:22-alpine
RUN addgroup -S appgroup && adduser -S appuser -G appgroup
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY --from=builder /app/package.json ./
EXPOSE 3000
USER appuser
CMD ["node", "dist/index.js"]

Python Service

FROM python:3.13-slim AS builder
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir --prefix=/install -r requirements.txt
COPY . .

FROM python:3.13-slim
RUN groupadd -r appgroup && useradd -r -g appgroup appuser
WORKDIR /app
COPY --from=builder /install /usr/local
COPY --from=builder /app .
EXPOSE 8000
USER appuser
CMD ["python", "-m", "uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

---

Step 4: Audit Checklist

CRITICAL (blocks grade A):
[ ] USER directive exists with non-root user
[ ] Multi-stage build (build tools not in final image)
[ ] Minimal base image (distroless/alpine preferred)
[ ] No secrets or credentials in image layers

HIGH (impacts CVE count):
[ ] Base image is up to date
[ ] Package versions are pinned
[ ] No development dependencies in final image

MEDIUM (best practices):
[ ] .dockerignore excludes .git, node_modules, etc.
[ ] COPY used instead of ADD
[ ] Build cache leveraged (COPY deps before source)

SUPPLY CHAIN (pipeline):
[ ] sbom: parameter in build-push-action
[ ] provenance: mode=max in build-push-action

---

Step 5: Generate Report

## Health Score Compliance

**Target:** Grade A
**Result:** [PASS|FAIL]

### Policy Results

| Policy | Status | Details |
|--------|--------|---------|
| Default non-root user | [PASS/FAIL] | USER [username] at line [N] |
| No fixable critical/high CVEs | [PASS/RISK] | Base: [image], [N] packages in final |
| No high-profile vulnerabilities | [PASS/RISK] | Base image [up to date/outdated] |
| No AGPL v3 licenses | [PASS/RISK] | [N] dependencies audited |
| Supply chain attestations | [PASS/MISSING] | sbom: [yes/no], provenance: [yes/no] |

## Actions Taken

| File | Action | Changes |
|------|--------|---------|
| Dockerfile | [CREATED/UPDATED] | [summary] |
| .dockerignore | [CREATED/UPDATED/UNCHANGED] | [summary] |

---

Severity Calibration

Severity	Criteria	Examples
CRITICAL	Blocks grade A	Missing USER, running as root, secrets in layers
HIGH	Causes CVE failures	Full debian base, unpinned versions, outdated base
MEDIUM	Reduces security posture	No .dockerignore, ADD instead of COPY, no multi-stage
LOW	Best practice deviation	Missing labels, suboptimal layer ordering