cache ci compliance config container containerd cyclonedx docker dockerfile github kubernetes license misconfig oci offline podman registry sarif sbom sca secret security spdx tar trivy vulnerability

DevSecOps: Scan Container Images with Trivy¶

Containers images ship software. They also ship vulnerabilities. Outdated base images, exposed secrets, misconfigured image instructions. Trivy scans container images for CVEs, misconfigurations, secrets, and license issues in one command.

TL;DR: Install Trivy, scan your container images with trivy image, enable additional scanners, and add it to your CI pipeline to catch vulnerabilities before deployment.

Install Trivy¶

# Ubuntu/Debian
sudo apt install apt-transport-https ca-certificates curl gnupg
curl -fsSL https://aquasecurity.github.io/trivy-repo/deb/public.key | sudo gpg --dearmor -o /usr/share/keyrings/trivy.gpg
echo "deb [signed-by=/usr/share/keyrings/trivy.gpg] https://aquasecurity.github.io/trivy-repo/deb $(lsb_release -sc) main" | sudo tee -a /etc/apt/sources.list.d/trivy.list
sudo apt update
sudo apt install trivy

Verify:

trivy --version

Scan a container image¶

Basic usage: scan a public image for vulnerabilities and secrets:

trivy image python:3.4-alpine

Vulnerability and secret scanning are both enabled by default. The output groups findings by OS package type, then gets into specific packages:

Report Summary

┌────────────────────────────────────────────────────────────────────────────┬────────────┬─────────────────┬─────────┐
│                                   Target                                   │    Type    │ Vulnerabilities │ Secrets │
├────────────────────────────────────────────────────────────────────────────┼────────────┼─────────────────┼─────────┤
│ python:3.4-alpine (alpine 3.9.2)                                           │   alpine   │       37        │    -    │
├────────────────────────────────────────────────────────────────────────────┼────────────┼─────────────────┼─────────┤
...

python:3.4-alpine (alpine 3.9.2)

Total: 37 (UNKNOWN: 0, LOW: 4, MEDIUM: 16, HIGH: 13, CRITICAL: 4)

┌──────────────┬────────────────┬──────────┬────────┬───────────────────┬───────────────┬──────────────────────────────────────────────────────────────┐
│   Library    │ Vulnerability  │ Severity │ Status │ Installed Version │ Fixed Version │                            Title                             │
├──────────────┼────────────────┼──────────┼────────┼───────────────────┼───────────────┼──────────────────────────────────────────────────────────────┤
│ expat        │ CVE-2018-20843 │ HIGH     │ fixed  │ 2.2.6-r0          │ 2.2.7-r0      │ expat: large number of colons in input makes parser consume  │
│              │                │          │        │                   │               │ high amount...                                               │
│              │                │          │        │                   │               │ https://avd.aquasec.com/nvd/cve-2018-20843                   │
...

To scan only vulnerabilities (disables the default secret scanner):

trivy image --scanners vuln python:3.4-alpine

To enable only misconfiguration or license scanning:

trivy image --scanners misconfig myapp:latest
trivy image --scanners license myapp:latest

Scan container image metadata¶

Container images have configuration metadata, the container image instructions that built them. Trivy can scan this configuration for misconfigurations and secrets:

# Dockerfile-style misconfigurations (USER, HEALTHCHECK, ADD vs COPY)
trivy image --image-config-scanners misconfig myapp:latest

# Secrets in environment variables (credential leaks in config)
trivy image --image-config-scanners secret myapp:latest

These are disabled by default. The misconfiguration scanner converts the image config into Dockerfile format and runs Dockerfile checks against it. The secret scanner looks for credentials in environment variables stored in the config JSON.

Scan an image tar file¶

Trivy can scan images saved as tar archives. Useful for offline or CI environments:

docker pull ruby:3.1-alpine3.15
docker save ruby:3.1-alpine3.15 -o ruby-3.1.tar
trivy image --input ruby-3.1.tar

Scan by architecture¶

By default, Trivy scans on the host's architecture. Cross-architecture images need the --platform flag:

trivy image --platform=linux/arm alpine:3.16.1

SBOM generation and vulnerability scanning¶

Trivy can generate Software Bill of Materials (SBOM) for container images:

# Generate SBOM in CycloneDX format
trivy image --format cyclonedx -o sbom.json python:3.4-alpine

# Generate SBOM in SPDX format
trivy image --format spdx-json -o sbom.json python:3.4-alpine

Compliance¶

The docker-cis-1.6.0 check evaluates container image configurations against the CIS Docker Benchmark:

trivy image --compliance docker-cis-1.6.0 myapp:latest

Authentication¶

For private registries, authenticate with:

trivy registry login --username myuser --password mypassword registry.example.com

Then scan as normal. Trivy reads the registry credentials before pulling the image.

Filter findings¶

Trivy lets you narrow scans by severity:

# Only HIGH and CRITICAL
trivy image --severity HIGH,CRITICAL alpine:3.18

# Only HIGH severity
trivy image --severity HIGH alpine:3.18

Add to CI/CD¶

# .github/workflows/trivy.yml
name: Trivy
on: [pull_request]
jobs:
  trivy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Run Trivy vulnerability scanner
        uses: aquasecurity/trivy-action@v0.36.0
        with:
          image-ref: myapp:latest
          format: table
          exit-code: 1
          severity: HIGH,CRITICAL

exit-code: 1 causes the job to fail on HIGH or CRITICAL findings. Use format: sarif and add the upload-sarif action for inline annotations.

Understand what Trivy scans¶

Trivy checks four categories against files inside container images:

Category	What it finds	Enabled by default
Vulnerabilities	CVEs in OS packages and language dependencies	Yes
Misconfigurations	IaC files inside the image (Kubernetes, Terraform)	No
Secrets	Hardcoded credentials, tokens, API keys	Yes
Licenses	Open source license compliance	No

Takeaways¶

Trivy scans for vulnerabilities and secrets by default. Use --scanners to enable misconfiguration and license scanning.
--image-config-scanners scans the image's configuration metadata, not the filesystem inside it.
--input lets you scan tar files and OCI layout directories instead of live registries. Useful for offline CI.
--severity and --exit-code control CI gating.
Use --platform for multi-arch images. Trivy only scans the host architecture without it.