Container Scanning and SBOM

Overview

Scan an image for CVEs, produce a Software Bill of Materials (SBOM), and decide fix vs accept risk for a release gate.

Trivy, Docker Scout, and registry scanners find known vulnerabilities. An SBOM inventories packages for compliance and incident response. Scanning without a triage process becomes noise.

This is a core tutorial in Module 12 · Container Scanning of the REBASH Academy Docker for Cloud & DevOps Engineers series — written for Cloud, DevOps, Platform, and SRE engineers.

Prerequisites

• Docker Security Hardening

Learning Objectives

By the end of this tutorial, you will be able to:

• Run Trivy (or Scout) against a local image
• Explain CRITICAL/HIGH triage
• Generate an SBOM (Syft/Trivy)
• List hardening moves that reduce findings

Architecture

This topic’s control points and relationships are shown below.

Theory

What

Vulnerability scanning analyses image contents for known Common Vulnerabilities and Exposures (CVEs). A Software Bill of Materials (SBOM) lists packages and dependencies you shipped. Tools such as Trivy, Docker Scout, Syft, and Grype integrate into CI to gate or inform releases.

Why

You cannot patch what you cannot see. Base OS packages and language libraries both introduce risk. SBOMs support incident response (“are we affected?”) and emerging compliance expectations. Failing CI on CRITICAL findings for production images is a common policy.

How it works

Scanners index installed packages and match them to vulnerability databases. Results include severity, fixed versions, and sometimes misconfiguration checks (Dockerfile smells). Generate an SBOM at build time and store it with the artefact. Fix order is usually: upgrade base image → upgrade application dependencies → rebuild → accept residual risk with a ticket if needed. Do not ignore OS packages because “we only care about the app language”.

Tool	Role
Trivy	OSS vuln + misconfig + SBOM
Docker Scout	Hub-integrated insights
Syft / Grype	SBOM + scan ecosystem

Key concepts

• CVE noise — triage by reachability and exploitability when possible
• Rebuild cadence — periodic rebuilds pick up base patches
• Private base images — control inheritance
• Sign + scan — complementary supply-chain controls

Wire scanners into both pull-request and main-branch pipelines so developers see findings early. Keep an allow-list process for accepted risks with expiry dates — permanent mute rules become invisible debt. After a major base-image upgrade, re-scan and redeploy even if application code did not change.

Common pitfalls

• Scanning once at project start and never again
• Suppressing all CVEs to keep CI green
• Treating SBOM generation as paperwork without storing it
• Scanning only the final stage while shipping a fat single-stage image

Hands-on Lab

Create a workspace for this tutorial.

mkdir -p ~/rebash-docker/module-12 && cd ~/rebash-docker/module-12

Focus: build an image and run a vulnerability scan when tools exist

Step 1 – Build + scan attempt

cat > Dockerfile << 'EOF'
FROM alpine:3.20
RUN apk add --no-cache curl
USER nobody
CMD ["curl", "--version"]
EOF
docker build -t rebash-scan:lab .
if command -v trivy >/dev/null; then
  trivy image --severity HIGH,CRITICAL rebash-scan:lab || true
else
  echo "Install Trivy or Docker Scout for CVE scanning"
  docker image inspect rebash-scan:lab --format '{{.Id}}'
fi
echo "Generate SBOMs in CI and store as artefacts" > sbom-notes.md

Step 2 – Cleanup image

docker rmi rebash-scan:lab

Final step – Cleanup note

docker rmi rebash-scan:lab 2>/dev/null || true
# Keep ~/rebash-docker/ for later tutorials

Validation

• Lab commands run under ~/rebash-docker/module-12/
• You can explain each Theory section in your own words
• You used modern tooling where it applies to this topic
• You can describe one production failure mode for this topic

Code Walkthrough

Production practice for Container Scanning and SBOM always combines:

1. Inspect before you change (status, plan, logs, dry-run)
2. Prefer reversible, documented changes (Git, IaC, drop-ins, version pins)
3. Capture evidence (command output, pipeline logs) for handovers
4. Prefer current tools and APIs over legacy shortcuts
5. Least privilege — escalate credentials only when required

Keep runbooks short enough to follow under pressure. Automate checks; keep humans for judgement.

Security Considerations

• Treat credentials and tokens for docker as privileged — never commit them
• Prefer short-lived auth (OIDC, roles, SSO) over long-lived keys
• Validate blast radius before apply/deploy/delete operations
• Restrict who can approve production changes
• Collect audit logs; limit who can read sensitive traces

Common Mistakes

Scanning once at project start and never again

Validate assumptions against the Theory section and official docs before changing production.

Suppressing all CVEs to keep CI green

Lab shortcuts (open security groups, admin roles, skip approvals) must not ship unchanged.

Changing production without a rollback path

Always know how to revert (previous artefact, prior release, state rollback, DNS failback).

Best Practices

• Encode Container Scanning and SBOM changes as code and review them in pull requests
• Pin versions (images, modules, actions, provider plugins)
• Separate environments with clear promotion gates
• Alert on symptoms with runbooks attached
• Destroy lab resources; tag everything with owner and expiry where possible

Troubleshooting

Symptom	Likely cause	Fix
Auth / permission denied	Wrong identity, policy, or scope	Check caller identity, roles, and least-privilege policies
Timeout / no route	Network, DNS, security group, or endpoint	Trace path, DNS, and allow-lists before retrying
Drift / unexpected plan	Manual change or wrong state/workspace	Reconcile desired vs actual; avoid click-ops on managed resources
Pipeline/job red	Flaky step, cache, or missing secret	Read failing step logs; bisect recent workflow/config changes
Cost spike	Idle load balancer, NAT, oversized compute	Inventory billable resources; stop/delete labs promptly

Summary

Container Scanning and SBOM is essential for Cloud and DevOps engineers working with docker. Practise the lab until the inspection and change path is muscle memory, then continue the track.

Interview Questions

1. What is an SBOM and why store it in CI?
2. How do you triage a CRITICAL CVE in a base image?
3. Scanner false positives — how do you handle them?
4. When should a pipeline fail on findings?
5. Difference between image scan and runtime detection?

Sample answer — question 2

Confirm the package is present in the final image and whether a fixed base exists.

Sample answer — question 4

Gate production on policy and keep SBOMs as artifacts for incident response.

Related Tutorials

• Course overview
• Container Logging and Monitoring

References

• Trivy · Docker Scout