tfsec (legacy) - migration reference

Companion reference for trivy-config. tfsec is transitioning to Trivy per Aqua Security's own guidance - the host skill is the forward path, and tfsec's checks ship inside trivy config. Keep this reference for an existing Terraform-only tfsec stack while the migration lands.

Overview

Per tfsec-home, tfsec is transitioning to Trivy, Aqua Security's consolidated scanner. For new projects, evaluate Trivy first; tfsec remains stable for existing usage.

When to use

• Existing tfsec project; team isn't ready to migrate to Trivy.
• Terraform-only stack; want a focused Terraform-specific scanner.
• A specific tfsec rule covers something Trivy doesn't yet.

How to use

1. Install tfsec via Homebrew or the release binary (Step 1).
2. Run tfsec . against the Terraform tree, starting at --minimum-severity HIGH to keep the signal high (Step 2).
3. Emit SARIF for GitHub Code Scanning, or JUnit / Markdown for CI and PR comments (Step 3).
4. Triage findings - fix real issues, annotate intentional exceptions with justified tfsec:ignore: comments (Step 4).
5. Verify: re-run tfsec . --minimum-severity HIGH after remediation and assert it reports no HIGH findings before merging; if any remain, fix or justify-ignore them and re-run.
6. Add custom YAML rules for team-specific policy, then wire the scan into CI (Steps 5-6).
7. Confirm cloud coverage; fall back to OPA / Conftest for unsupported clouds (Step 7).
8. Plan the Trivy migration for new work, and combine with Checkov / KICS for overlapping coverage (Steps 8-9).

Step 1 - Install

# macOS
brew install tfsec

# Linux
curl -L https://github.com/aquasecurity/tfsec/releases/latest/download/tfsec-linux-amd64 \
  -o /usr/local/bin/tfsec
chmod +x /usr/local/bin/tfsec

Step 2 - Run

# Scan current directory
tfsec .

# Scan specific path
tfsec ./terraform/

# Concise output
tfsec . --concise-output

# Specific severity threshold
tfsec . --minimum-severity HIGH

Step 3 - Output formats

Per tfsec-home: "JSON and SARIF output capabilities for integration with external tools and workflows."

# JSON
tfsec . -f json > tfsec.json

# SARIF (GitHub Code Scanning)
tfsec . -f sarif -O tfsec.sarif

# JUnit XML
tfsec . -f junit -O tfsec.xml

# Markdown (PR comments)
tfsec . -f markdown

Step 4 - Skip checks

# Skip specific checks
tfsec . -e aws-s3-enable-bucket-encryption,aws-s3-enable-versioning

# Skip everything matching a pattern
tfsec . -e aws-s3-*

Inline:

# main.tf
resource "aws_s3_bucket" "public_data" {
  # tfsec:ignore:aws-s3-enable-bucket-encryption Public dataset, not encrypted by design
  # tfsec:ignore:aws-s3-enable-bucket-logging Public CDN, no audit logging needed
  bucket = "my-public-data"
  acl    = "public-read"
}

Step 5 - Custom rules

Author custom YAML rules for team-specific policy the built-in set misses: tfsec-custom-rules-and-ci.md.

Step 6 - CI integration

Run the official tfsec action with SARIF upload to GitHub Code Scanning: tfsec-custom-rules-and-ci.md.

Step 7 - Supported clouds

Per tfsec-home, tfsec covers AWS (S3, EC2, RDS, IAM, Lambda, API Gateway, and 30+ services), Azure (App Service, Storage, Database, Container, Key Vault), Google Cloud (Compute, GKE, SQL, Storage, IAM, BigQuery), plus Kubernetes, OpenStack, Oracle, DigitalOcean, and CloudStack.

For unsupported clouds, fall back to OPA / Conftest with custom Rego per policy-as-code-runner.

Step 8 - Migration to Trivy

Per tfsec-home guidance:

# Install Trivy
brew install trivy   # or apt-get / etc.

# Trivy includes tfsec's checks under `trivy config`
trivy config ./terraform/

The migration is mostly mechanical - Trivy ingests the same .tf files; rule names may differ.

Step 9 - Combine with Checkov + KICS

Multiple scanners catch overlapping but non-identical issues. tfsec is faster and Terraform-specific; Checkov (checkov-policy) is broader; the KICS tool adds different rule classes.

tfsec . -f json > tfsec.json
checkov -d . -o json > checkov.json
kics scan -p . --report-formats json
# unify results across the three scanners

Worked example

A team runs tfsec on an AWS Terraform module while planning a Trivy migration.

1. brew install tfsec, then tfsec ./terraform/ --minimum-severity HIGH to focus on the worst findings first.
2. tfsec flags an unencrypted S3 bucket (aws-s3-enable-bucket-encryption) as HIGH.
3. The bucket is a public dataset by design, so the author adds # tfsec:ignore:aws-s3-enable-bucket-encryption Public dataset, not encrypted by design inline.
4. CI runs aquasecurity/tfsec-action@v1.0.3 with format: sarif; the SARIF upload posts remaining findings to the Security tab.
5. Ahead of the switch they dry-run trivy config ./terraform/ and confirm the same .tf files scan under Trivy.

Result: HIGH-severity misconfigurations gate the build, intentional exceptions are documented inline, and the Trivy forward-path is validated before switching.

Anti-patterns

Limitations

• Terraform-only. Doesn't scan Kubernetes / Dockerfile / CloudFormation directly (Trivy expands).
• Maintenance pace slowing. Per tfsec-home, tfsec gets bug fixes but not new features.
• Some new cloud services lag in coverage. Newer AWS / Azure resources may not have rules yet.
• No baseline support out of the box. Adopt against legacy via skip annotations or wrapper scripts.

References

• tfs - tfsec overview, transition-to-Trivy positioning, developer-friendly output, AWS / Azure / GCP / Kubernetes / OpenStack / Oracle / DigitalOcean / CloudStack support, JSON / SARIF output.
• Custom YAML rules + CI workflow: tfsec-custom-rules-and-ci.md.
• checkov-policy - sister scanner.
• policy-as-code-runner - custom OPA / Rego policies (for unsupported clouds or custom rules).