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sec-actions/scan-image/README.md
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# Trivy scan (image)
Composite action that runs **`trivy image`** inside **Docker** with the same hardening style as [setup-db](../setup-db): read-only root filesystem, dropped capabilities, `no-new-privileges`, AppArmor `docker-default`, a private `tmpfs` on `/tmp`, and resource limits.
You pass a pullable **`image`** reference (e.g. `alpine:3.20` or a digest). Trivy pulls and scans it inside the container. The Trivy cache from [setup-db](../setup-db) is mounted **read-only** at `/cache` (**`--skip-db-update`** avoids re-downloading the DB). Your **`output-dir`** is mounted **read-write** at `/out`; the report is written as **`output-file`** inside that directory. The report format is always **SARIF** (`--format sarif`). Trivy is always run with **`--offline-scan`** (no API calls to identify dependencies) and **`--exit-code 0`** (the step succeeds after writing the report even when findings are present). Image layers are still pulled over the network when needed.
**Image scans need network access** to pull the image (and possibly layers). This action does **not** set `--network none` (unlike [scan-config](../scan-config) and [scan-fs](../scan-fs)).
**Bind mounts:** Prefer **`cache-dir`** and **`output-dir`** under **`github.workspace`** (the default cache path does). Paths under **`runner.temp`** can fail on some runners—see [setup-db](../setup-db) README.
## Prerequisites
- Docker on the runner.
- A populated Trivy cache at **`cache-dir`** (typically from the [setup-db](../setup-db) action).
## Usage
```yaml
- name: Setup Trivy DB cache
id: db
uses: ./setup-db
- name: Image scan
id: scan
uses: ./scan-image
with:
image: alpine:3.20
cache-dir: ${{ steps.db.outputs.cache-dir }}
output-dir: ${{ github.workspace }}/trivy-reports
output-file: image.sarif
- name: Upload report
uses: actions/upload-artifact@v4
with:
name: trivy-image
path: ${{ steps.scan.outputs.output-path }}
```
## Inputs
| Input | Description | Required | Default |
| --------------- | --------------------------------------------------------------------------- | -------- | ------- |
| `image` | Image reference to scan (pulled inside the container) | Yes | — |
| `cache-dir` | Trivy cache directory (mounted read-only at `/cache`; created if missing) | No | `${{ github.workspace }}/.trivy-cache` |
| `output-dir` | Host directory for the report (mounted read-write at `/out`; created if missing) | Yes | — |
| `output-file` | SARIF file name only (no `/`); created under `output-dir` | Yes | — |
| `trivy-version` | Trivy Docker image (digest pin recommended) | No | Same pin as `setup-db` / see `action.yaml` |
**`trivy-version` is optional.** Omit it to use the default image from `action.yaml`.
## Outputs
| Output | Description |
| -------------- | ------------------------------------ |
| `output-path` | Absolute path to the SARIF report on the host |
## Notes
- **`cache-dir`** and **`output-dir`** are created with `mkdir -p` if missing (required for Docker bind mounts).
- Local-only images (e.g. built on the host) are not supported unless they are available to the **inner** Docker pull (this action does not mount `docker.sock`).
- The step still fails if Docker or the container exits non-zero before Trivy completes (e.g. mount or runtime errors).