vexctl: A tool to make VEX work

vexctl is a tool to create, apply, and attest VEX (Vulnerability Exploitability eXchange) data. Its purpose is to help with the creation and management of VEX documents that allow "turning off" security scanner alerts of vulnerabilities known not to affect a product.

VEX can be thought of as a "negative security advisory". Using VEX, software authors can communicate to their users that an otherwise vulnerable component has no security implications for their product.

Installing

If you have Go 1.16 or later installed, you can run the following to install vexctl:

go install github.com/openvex/vexctl@latest

Operational Model

To achieve its mission, vexctl has three main modes of operation:

1. Creating VEX documents
2. Wrapping VEX documents in signed attestations
3. Applying the VEX data to scanner results

1. Creating VEX Documents

Creating New VEX Documents

VEX data can be created to a file on disk, or it can be captured in a signed attestation that can be attached to a container image.

The easiest way to create a VEX document is using the vexctl create command:

vexctl create --product="pkg:apk/wolfi/git@2.38.1-r0?arch=x86_64" \
               --vuln="CVE-2014-123456" \
               --status="not_affected" \
               --justification="inline_mitigations_already_exist"

The previous invocations creates a VEX document with a single statement asserting that the WolfiOS package git-2.38.1-r0 is not affected by CVE-2014-123456 because it has already been mitigated in the distribution.

This is the resulting document:

{
  "@context": "https://openvex.dev/ns",
  "@id": "https://openvex.dev/docs/public/vex-23429cd0c468676c544579ddc118d76b5aa52aff8203c332d2c14dc2a415a551",
  "author": "Unknown Author",
  "role": "Document Creator",
  "timestamp": "2023-02-03T08:10:46.087206-07:00",
  "version": "1",
  "statements": [
    {
      "vulnerability": "CVE-2014-123456",
      "products": [
        "pkg:apk/wolfi/git@2.38.1-r0?arch=x86_64"
      ],
      "status": "not_affected",
      "justification": "inline_mitigations_already_exist"
    }
  ]
}

vexctl can create VEX documents from three different sources:

1. From the command line, as shown
2. From a golden file of predefined rules
3. From merging other VEX documents into a new one

The data is generated from a known rule set (the Golden Data) which is reused and reapplied to new releases of the same project.

Merging Existing Documents

When more than one stakeholder is issuing VEX metadata about a piece of software, vexctl can merge the documents to get the most up-to-date impact assessment of a vulnerability. The following example can be run using the test documents found in this repository:

vexctl merge --product=pkg:apk/wolfi/bash@1.0.0 \
             pkg/ctl/testdata/document1.vex.json \
             pkg/ctl/testdata/document2.vex.json

The resulting document combines the VEX statements that express data about bash@1.0.0 into a single document that tells the whole story of how CVE-2014-123456 was under_investigation and then fixed four hours later:

{
  "@context": "",
  "@id": "merged-vex-67124ea942ef30e1f42f3f2bf405fbbc4f5a56e6e87684fc5cd957212fa3e025",
  "author": "Unknown Author",
  "role": "Document Creator",
  "timestamp": "2023-02-03T08:11:42.525456-07:00",
  "version": "",
  "statements": [
    {
      "vulnerability": "CVE-1234-5678",
      "timestamp": "2022-12-22T16:36:43-05:00",
      "products": [
        "pkg:apk/wolfi/bash@1.0.0"
      ],
      "status": "under_investigation"
    },
    {
      "vulnerability": "CVE-1234-5678",
      "timestamp": "2022-12-22T20:56:05-05:00",
      "products": [
        "pkg:apk/wolfi/bash@1.0.0"
      ],
      "status": "fixed"
    }
  ]
}

2. Attesting Examples

# Attest and attach VEX statements in mydata.vex.json to a container image:
vexctl attest --attach --sign mydata.vex.json cgr.dev/image@sha256:e4cf37d568d195b4..

3. VEXing a Results Set

Using statements in a VEX document or from an attestation, vexctl will filter security scanner results to remove VEX'ed out entries.

Filtering Examples

# From a VEX file:
vexctl filter scan_results.sarif.json vex_data.csaf

# From a stored VEX attestation:
vexctl filter scan_results.sarif.json cgr.dev/image@sha256:e4cf37d568d195b4b5af4c36a...

The output from both examples will be the same: the SARIF result data, but without the vulnerabilities that were stated as not exploitable:

{
  "version": "2.1.0",
  "$schema": "https://json.schemastore.org/sarif-2.1.0-rtm.5.json",
  "runs": [
    {
      "tool": {
        "driver": {
          "fullName": "Trivy Vulnerability Scanner",
          "informationUri": "https://github.com/aquasecurity/trivy",
          "name": "Trivy",
          "rules": [

We support results files in SARIF for now. We plan to add support for the proprietary formats of the most popular scanners.

Multiple VEX Files

Assessing impact is process that takes time. VEX is designed to communicate with users as time progresses. An example timeline may look like this:

1. A project becomes aware of CVE-2014-123456, associated with one of its components.
2. Developers issue a VEX data file with a status of under_investigation to inform their users they are aware of the CVE but are checking what impact it has.
3. After investigation, the developers determine the CVE has no impact in their project because the vulnerable function in the component is never executed.
4. They issue a second VEX document with a status of not_affected and using the vulnerable_code_not_in_execute_path justification.

vexctl will read all the documents in chronological order and "replay" the known impacts statuses the order they were found, effectively computing the not_affected status.

If a SARIF report is VEX'ed with vexctl any entries alerting of CVE-2014-123456 will be filtered out.

Build vexctl

To build vexctl, clone this repository and run make.

$ git clone https://github.com/openvex/vexctl.git
$ cd vex
$ make
$ ./vexctl version
 _   _  _____ __   __ _____  _____  _
| | | ||  ___|\ \ / //  __ \|_   _|| |
| | | || |__   \ V / | /  \/  | |  | |
| | | ||  __|  /   \ | |      | |  | |
\ \_/ /| |___ / /^\ \| \__/\  | |  | |____
 \___/ \____/ \/   \/ \____/  \_/  \_____/
vexctl: A tool for working with VEX data

GitVersion:    v0.1.0-21-g769ba3f-dirty
GitCommit:     769ba3f0c638003b6c5e3c41ae88f4cdc63555ab
GitTreeState:  dirty
BuildDate:     2023-01-18T00:19:24Z
GoVersion:     go1.19.4
Compiler:      gc
Platform:      darwin/arm64