# Source: https://github.com/aquasecurity/trivy/blob/main/docs/guide/supply-chain/attestation/rekor.md

# Scan SBOM attestation in Rekor

!!! warning "EXPERIMENTAL"
    This feature might change without preserving backwards compatibility.

## Container images
Trivy can retrieve SBOM attestation of the specified container image in the [Rekor][rekor] instance and scan it for vulnerabilities.

### Prerequisites
1. SBOM attestation stored in Rekor
    - See [the "Keyless signing" section][sbom-attest] if you want to upload your SBOM attestation to Rekor.
 

### Scanning
You need to pass `--sbom-sources rekor` so that Trivy will look for SBOM attestation in Rekor.

!!! note
    `--sbom-sources` can be used only with `trivy image` at the moment.

```bash
$ trivy image --sbom-sources rekor otms61/alpine:3.7.3                                                                            [~/src/github.com/aquasecurity/trivy]
2022-09-16T17:37:13.258+0900	INFO	Vulnerability scanning is enabled
2022-09-16T17:37:13.258+0900	INFO	Secret scanning is enabled
2022-09-16T17:37:13.258+0900	INFO	If your scanning is slow, please try '--scanners vuln' to disable secret scanning
2022-09-16T17:37:13.258+0900	INFO	Please see also https://trivy.dev/dev/docs/secret/scanning/#recommendation for faster secret detection
2022-09-16T17:37:14.827+0900	INFO	Detected SBOM format: cyclonedx-json
2022-09-16T17:37:14.901+0900	INFO	Found SBOM (cyclonedx) attestation in Rekor
2022-09-16T17:37:14.903+0900	INFO	Detected OS: alpine
2022-09-16T17:37:14.903+0900	INFO	Detecting Alpine vulnerabilities...
2022-09-16T17:37:14.907+0900	INFO	Number of language-specific files: 0
2022-09-16T17:37:14.908+0900	WARN	This OS version is no longer supported by the distribution: alpine 3.7.3
2022-09-16T17:37:14.908+0900	WARN	The vulnerability detection may be insufficient because security updates are not provided

otms61/alpine:3.7.3 (alpine 3.7.3)
==================================
Total: 2 (UNKNOWN: 0, LOW: 0, MEDIUM: 0, HIGH: 0, CRITICAL: 2)

┌────────────┬────────────────┬──────────┬───────────────────┬───────────────┬──────────────────────────────────────────────────────────┐
│  Library   │ Vulnerability  │ Severity │ Installed Version │ Fixed Version │                          Title                           │
├────────────┼────────────────┼──────────┼───────────────────┼───────────────┼──────────────────────────────────────────────────────────┤
│ musl       │ CVE-2019-14697 │ CRITICAL │ 1.1.18-r3         │ 1.1.18-r4     │ musl libc through 1.1.23 has an x87 floating-point stack │
│            │                │          │                   │               │ adjustment im ......                                     │
│            │                │          │                   │               │ https://avd.aquasec.com/nvd/cve-2019-14697               │
├────────────┤                │          │                   │               │                                                          │
│ musl-utils │                │          │                   │               │                                                          │
│            │                │          │                   │               │                                                          │
│            │                │          │                   │               │                                                          │
└────────────┴────────────────┴──────────┴───────────────────┴───────────────┴──────────────────────────────────────────────────────────┘

```

If you have your own Rekor instance, you can specify the URL via `--rekor-url`.

```bash
$ trivy image --sbom-sources rekor --rekor-url https://my-rekor.dev otms61/alpine:3.7.3
```

## Non-packaged binaries
Trivy can retrieve SBOM attestation of non-packaged binaries in the [Rekor][rekor] instance and scan it for vulnerabilities.

### Prerequisites
1. SBOM attestation stored in Rekor
    - See [the "Keyless signing" section][sbom-attest] if you want to upload your SBOM attestation to Rekor.

Cosign currently does not support keyless signing for blob attestation, so use our plugin at the moment.
This example uses a cat clone [bat][bat] written in Rust.
You need to generate SBOM from lock files like `Cargo.lock` at first.

```bash
$ git clone -b v0.20.0 https://github.com/sharkdp/bat
$ trivy fs --format cyclonedx --output bat.cdx ./bat/Cargo.lock
```

Then [our attestation plugin][plugin-attest] allows you to store the SBOM attestation linking to a `bat` binary in the Rekor instance.

```bash
$ wget https://github.com/sharkdp/bat/releases/download/v0.20.0/bat-v0.20.0-x86_64-apple-darwin.tar.gz
$ tar xvf bat-v0.20.0-x86_64-apple-darwin.tar.gz
$ trivy plugin install github.com/aquasecurity/trivy-plugin-attest
$ trivy attest --predicate ./bat.cdx --type cyclonedx ./bat-v0.20.0-x86_64-apple-darwin/bat
```

!!! note
    The public instance of the Rekor maintained by the Sigstore team limits the attestation size.
    If you are using the public instance, please make sure that your SBOM is small enough.
    To get more detail, please refer to the Rekor project's [documentation](https://github.com/sigstore/rekor#public-instance).

### Scan a non-packaged binary
Trivy calculates the digest of the `bat` binary and searches for the SBOM attestation by the digest in Rekor.
If it is found, Trivy uses that for vulnerability scanning.

```bash
$ trivy fs --sbom-sources rekor ./bat-v0.20.0-x86_64-apple-darwin/bat
2022-10-25T13:27:25.950+0300    INFO    Found SBOM attestation in Rekor: bat
2022-10-25T13:27:25.993+0300    INFO    Number of language-specific files: 1
2022-10-25T13:27:25.993+0300    INFO    Detecting cargo vulnerabilities...

bat (cargo)
===========
Total: 1 (UNKNOWN: 0, LOW: 0, MEDIUM: 0, HIGH: 1, CRITICAL: 0)

┌───────────┬───────────────────┬──────────┬───────────────────┬───────────────┬────────────────────────────────────────────────────────────┐
│  Library  │   Vulnerability   │ Severity │ Installed Version │ Fixed Version │                           Title                            │
├───────────┼───────────────────┼──────────┼───────────────────┼───────────────┼────────────────────────────────────────────────────────────┤
│ regex     │ CVE-2022-24713    │ HIGH     │ 1.5.4             │ 1.5.5         │ Mozilla: Denial of Service via complex regular expressions │
│           │                   │          │                   │               │ https://avd.aquasec.com/nvd/cve-2022-24713                 │
└───────────┴───────────────────┴──────────┴───────────────────┴───────────────┴────────────────────────────────────────────────────────────┘
```

Also, it is applied to non-packaged binaries even in container images.

```bash
$ trivy image --sbom-sources rekor --scanners vuln alpine-with-bat
2022-10-25T13:40:14.920+0300    INFO    Vulnerability scanning is enabled
2022-10-25T13:40:18.047+0300    INFO    Found SBOM attestation in Rekor: bat
2022-10-25T13:40:18.186+0300    INFO    Detected OS: alpine
2022-10-25T13:40:18.186+0300    INFO    Detecting Alpine vulnerabilities...
2022-10-25T13:40:18.199+0300    INFO    Number of language-specific files: 1
2022-10-25T13:40:18.199+0300    INFO    Detecting cargo vulnerabilities...

alpine-with-bat (alpine 3.15.6)
===============================
Total: 0 (UNKNOWN: 0, LOW: 0, MEDIUM: 0, HIGH: 0, CRITICAL: 0)


bat (cargo)
===========
Total: 4 (UNKNOWN: 3, LOW: 0, MEDIUM: 0, HIGH: 1, CRITICAL: 0)

┌───────────┬───────────────────┬──────────┬───────────────────┬───────────────┬────────────────────────────────────────────────────────────┐
│  Library  │   Vulnerability   │ Severity │ Installed Version │ Fixed Version │                           Title                            │
├───────────┼───────────────────┼──────────┼───────────────────┼───────────────┼────────────────────────────────────────────────────────────┤
│ regex     │ CVE-2022-24713    │ HIGH     │ 1.5.4             │ 1.5.5         │ Mozilla: Denial of Service via complex regular expressions │
│           │                   │          │                   │               │ https://avd.aquasec.com/nvd/cve-2022-24713                 │
└───────────┴───────────────────┴──────────┴───────────────────┴───────────────┴────────────────────────────────────────────────────────────┘
```


!!! note
    The `--sbom-sources rekor` flag slows down the scanning as it queries Rekor on the Internet for all non-packaged binaries.

[rekor]: https://github.com/sigstore/rekor
[sbom-attest]: sbom.md#keyless-signing

[plugin-attest]: https://github.com/aquasecurity/trivy-plugin-attest

[bat]: https://github.com/sharkdp/bat