seikaikyo/scanning-iac-and-images-with-trivy

Scanning IaC and Images with Trivy

Overview

Trivy (by Aqua Security) is a comprehensive, open-source security scanner that finds vulnerabilities (CVEs), misconfigurations (IaC), secrets, software licenses, and software supply-chain weaknesses across a wide range of targets: container images, filesystems, Git repositories, virtual machine images, Kubernetes clusters, and SBOM documents. It is widely adopted as a "shift-left" gate in CI/CD pipelines because it is fast, runs as a single static binary, requires no agent, and supports machine-readable output formats (JSON, SARIF, CycloneDX, SPDX) for integration with code-scanning dashboards.

Trivy bundles four primary scanners that can be toggled with --scanners:

• vuln — OS package and language-dependency vulnerability detection (CVE matching against the Trivy vulnerability DB).
• misconfig — Infrastructure-as-Code and configuration misconfiguration detection (Terraform, CloudFormation, Kubernetes manifests, Dockerfile, Helm) using built-in and custom Rego policies.
• secret — Hard-coded secret/credential detection (API keys, tokens, private keys).
• license — Software license identification and policy enforcement.

This skill covers building a Trivy-based scanning workflow that gates a CI/CD pipeline: scanning images before push, scanning IaC before apply, generating and re-scanning SBOMs, and failing builds on policy violations. Detecting these weaknesses defends against the MITRE ATT&CK technique T1525 (Implant Internal Image), where adversaries plant malicious or vulnerable images in a registry to be deployed across the environment.

When to Use

• When integrating vulnerability and misconfiguration scanning into a CI/CD pipeline as a quality/security gate before images are pushed or infrastructure is applied.
• When auditing container images in a registry for known CVEs prior to deployment.
• When validating Terraform, CloudFormation, Kubernetes, Dockerfile, or Helm IaC for security misconfigurations.
• When generating an SBOM (CycloneDX/SPDX) for supply-chain transparency and later re-scanning that SBOM for newly disclosed CVEs.
• When scanning a running Kubernetes cluster for vulnerable workloads and misconfigured RBAC/resources.
• When enforcing license compliance policy on dependencies.

Prerequisites

• A Linux/macOS/Windows host or CI runner with network access to download the Trivy vulnerability database.
• Docker (optional) if scanning local images by name or using the containerized Trivy.
• Install Trivy (Aqua Security official methods):

# Debian/Ubuntu (APT repository)
sudo apt-get install -y wget gnupg
wget -qO - https://aquasecurity.github.io/trivy-repo/deb/public.key | gpg --dearmor | sudo tee /usr/share/keyrings/trivy.gpg > /dev/null
echo "deb [signed-by=/usr/share/keyrings/trivy.gpg] https://aquasecurity.github.io/trivy-repo/deb generic main" | sudo tee /etc/apt/sources.list.d/trivy.list
sudo apt-get update
sudo apt-get install -y trivy

# RHEL/CentOS (YUM repository), macOS (Homebrew), and install script
brew install trivy
curl -sfL https://raw.githubusercontent.com/aquasecurity/trivy/main/contrib/install.sh | sudo sh -s -- -b /usr/local/bin

# Containerized usage (no install)
docker run --rm -v /var/run/docker.sock:/var/run/docker.sock aquasec/trivy:latest image python:3.10-alpine

# Verify
trivy --version

• For air-gapped or rate-limited environments, pre-download the DB with trivy image --download-db-only and the Java/policy bundles as needed.

Objectives

• Scan a container image for OS and language vulnerabilities and fail the build above a severity threshold.
• Scan IaC (Terraform/Kubernetes/Dockerfile) for misconfigurations.
• Detect hard-coded secrets in a repository or filesystem.
• Generate a CycloneDX or SPDX SBOM and re-scan it for vulnerabilities.
• Emit SARIF for GitHub code scanning and JSON for programmatic gating.
• Wire Trivy into a CI/CD pipeline with --exit-code to enforce policy.

MITRE ATT&CK Mapping

| Technique ID | Name | Tactic | Relevance | |--------------|------|--------|-----------| | T1525 | Implant Internal Image | Persistence | Trivy detects vulnerable or malicious images/layers and embedded secrets before they are implanted in a registry and propagated to running workloads. |

Workflow

1. Scan a container image for vulnerabilities

Run a vulnerability-only scan of a registry image, restricting to high/critical findings and ignoring CVEs with no available fix:

trivy image \
  --scanners vuln \
  --severity HIGH,CRITICAL \
  --ignore-unfixed \
  --format table \
  python:3.10-alpine

Scan an image saved as a tarball (useful when the image is built but not yet pushed):

docker save myorg/app:1.4.0 -o app.tar
trivy image --input app.tar --severity CRITICAL --format json --output app-vulns.json

2. Enable multiple scanners on an image

Run vulnerability, misconfiguration, secret, and license scanners together:

trivy image \
  --scanners vuln,misconfig,secret,license \
  --severity MEDIUM,HIGH,CRITICAL \
  myorg/app:1.4.0

Scan the image's embedded config (Dockerfile-equivalent build history and history secrets):

trivy image --image-config-scanners misconfig,secret myorg/app:1.4.0

3. Scan Infrastructure-as-Code (misconfiguration)

Scan a directory of Terraform / Kubernetes / Dockerfile / Helm / CloudFormation for misconfigurations using the config target:

# Scan a Terraform / IaC directory
trivy config \
  --severity HIGH,CRITICAL \
  --format table \
  ./infra

# Scan with custom Rego policies and a specific policy namespace
trivy config \
  --config-policy ./policies \
  --policy-namespaces user \
  ./infra

Alternatively use the fs (filesystem) target with the misconfig scanner explicitly:

trivy fs --scanners misconfig,secret --severity HIGH,CRITICAL ./infra

4. Scan a repository and detect secrets

Scan a local working tree (or remote repo) for vulnerabilities in lockfiles and hard-coded secrets:

# Local filesystem (dependencies + secrets)
trivy fs --scanners vuln,secret --severity HIGH,CRITICAL .

# Remote Git repository
trivy repository --scanners vuln,secret https://github.com/myorg/myrepo

5. Generate and re-scan an SBOM

Produce a CycloneDX SBOM from an image, then scan the SBOM itself for vulnerabilities (so a stored SBOM can be re-evaluated as new CVEs are disclosed):

# Generate CycloneDX SBOM
trivy image --format cyclonedx --output sbom.cdx.json myorg/app:1.4.0

# Generate SPDX SBOM
trivy image --format spdx-json --output sbom.spdx.json myorg/app:1.4.0

# Re-scan the SBOM for vulnerabilities later
trivy sbom --severity HIGH,CRITICAL sbom.cdx.json

6. Emit SARIF for code-scanning dashboards

Produce SARIF for GitHub Advanced Security / code scanning ingestion:

trivy image \
  --format sarif \
  --output trivy-results.sarif \
  --severity HIGH,CRITICAL \
  myorg/app:1.4.0

7. Gate the CI/CD pipeline with exit codes

Use --exit-code 1 so the pipeline step fails when findings at or above the chosen severity are present. Separate the "report everything" run (exit 0) from the "enforce" run (exit 1):

# 1) Informational report (never fails the build)
trivy image --severity LOW,MEDIUM,HIGH,CRITICAL --exit-code 0 --format table myorg/app:1.4.0

# 2) Enforcement gate (fails build on HIGH/CRITICAL with a fix available)
trivy image \
  --severity HIGH,CRITICAL \
  --ignore-unfixed \
  --exit-code 1 \
  --format json --output gate.json \
  myorg/app:1.4.0

Example GitHub Actions step using the official action:

- name: Run Trivy image scan (gate)
  uses: aquasecurity/trivy-action@master
  with:
    image-ref: 'myorg/app:1.4.0'
    format: 'sarif'
    output: 'trivy-results.sarif'
    severity: 'HIGH,CRITICAL'
    ignore-unfixed: true
    exit-code: '1'

8. Manage false positives and the DB

Suppress accepted-risk findings with a .trivyignore file and keep the DB current:

# .trivyignore — one CVE/AVD/secret rule ID per line
echo "CVE-2023-12345" >> .trivyignore
echo "AVD-AWS-0089"   >> .trivyignore

# Refresh DBs explicitly (useful for caching layers in CI)
trivy image --download-db-only
trivy image --download-java-db-only

# Scan a Kubernetes cluster (summary report)
trivy k8s --report summary --severity HIGH,CRITICAL cluster

Tools and Resources

| Tool / Resource | Purpose | Link | |------------------|---------|------| | Trivy | Core scanner CLI | https://github.com/aquasecurity/trivy | | Trivy Documentation | Official docs (targets, scanners, flags) | https://trivy.dev/latest/docs/ | | trivy-action | GitHub Actions integration | https://github.com/aquasecurity/trivy-action | | Trivy Operator | In-cluster Kubernetes continuous scanning | https://github.com/aquasecurity/trivy-operator | | Trivy vulnerability DB | OSS vulnerability data source | https://github.com/aquasecurity/trivy-db | | CycloneDX | SBOM standard emitted by Trivy | https://cyclonedx.org/ |

Validation Criteria

• [ ] Trivy installed and trivy --version reports a valid version.
• [ ] Container image scanned for vulnerabilities with severity filtering applied.
• [ ] Image scanned with multiple scanners (vuln, misconfig, secret, license).
• [ ] IaC directory scanned with trivy config and misconfigurations reviewed.
• [ ] Secret scanning run against the repository.
• [ ] CycloneDX/SPDX SBOM generated and successfully re-scanned with trivy sbom.
• [ ] SARIF output produced for the code-scanning dashboard.
• [ ] CI/CD gate fails the build on HIGH/CRITICAL findings via --exit-code 1.
• [ ] .trivyignore configured for accepted-risk findings with documented justification.