OS Hardening as Code, Episode 5
Cloud AMI Security Risks · Linux Hardening as Code · Multi-Cloud OS Hardening · Automated OpenSCAP Compliance · CI/CD Compliance Gate**

Note: the tool in this series was released as Stratum and renamed to BakeX at
v0.6.0 — same project, same license, same team. Commands below use the current bakex
CLI. If you arrived here looking for stratum or pip install stratumoss, you’re in the
right place: github.com/invicton/bakex.

TL;DR

• A CI/CD compliance gate turns an OS hardening grade from a report into a build constraint — unhardened images fail the pipeline before they can be deployed
• POST /api/pipeline/scan scores an image against a pass_threshold and a severity_threshold, and returns a passed boolean
• The endpoint returns HTTP 200 even when the gate fails. curl -sf will not catch it — you must parse .passed. This is the single most important detail on this page
• The gate is two-dimensional: a score floor and a severity ceiling, so one critical finding blocks a release that scores 94
• GitHub Actions, GitLab CI, Jenkins, and Tekton integrations are one curl plus one jq
• The structural guarantee: an image that doesn’t pass the gate doesn’t reach the deploy job

The Problem: A Grade No One Checks Is Decoration

Pipeline without compliance gate:
  Build → Test → Security scan (results to dashboard) → Deploy

What actually happens:
  Build → Test → Security scan → "C grade, but we need to ship" → Deploy anyway
                                           │
                                           └─ Dashboard shows C grade
                                              Nobody is paged
                                              Deployment succeeds

A CI/CD compliance gate means the pipeline can’t continue if the grade is below threshold.

EP04 showed that automated OpenSCAP compliance gives every image a verified, reproducible grade before deployment. What it assumed is that someone checks the grade before deploying. They don’t — not under deadline pressure, not when the image has been “working fine for months,” not at 2am.

The same problem that made hardening runbooks skippable applies to compliance grades: if checking the grade is a discretionary step, it will be skipped.

A new microservice was deployed from an unhardened base image. The team had built it quickly during a sprint, used a community AMI as the base, and planned to harden it “in the next sprint.”

Three weeks later, a penetration test found it. SSH password authentication enabled. Three unnecessary services running — one of them with a known CVE. The finding: the instance had full inbound access from the VPC and was reachable from a compromised adjacent instance.

The deployment had gone through the normal CI/CD pipeline. Unit tests passed. Integration tests passed. A vulnerability scan ran. The scan produced a report that went to a dashboard. Nobody had a gate set up to fail the build if the image was unhardened.

The hardening work from the “next sprint” plan would have taken four hours. The pentest remediation took a week, plus the time to investigate what had been exposed during the three weeks the instance was running.

The CI/CD pipeline had every check except the one that would have caught the base image problem before the first deployment.

The Pipeline API

The Pipeline API is a single HTTP endpoint that takes an image ID, scans it, and returns a verdict:

curl -s -X POST https://bakex.yourdomain.com/api/pipeline/scan \
  -H "X-API-Key: ${BAKEX_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{
    "image_id": "ami-0a7f3c9e82d1b4c05",
    "provider": "aws",
    "region": "us-east-1",
    "pass_threshold": 75.0,
    "severity_threshold": "high",
    "wait": true
  }'

Authentication takes either X-API-Key or Authorization: Bearer; keys are created at
/settings/api-keys. With wait: true the request blocks until the scan completes — which is what
you want in CI, where a job that returns before the answer exists is worse than a slow one. There’s
a timeout_seconds (default 900) for when it doesn’t.

The response is the same shape whether you passed or failed:

{
  "job_id": "7f3c9e82-4d1b-4c05-a7f3-c9e82d1b4c05",
  "status": "complete",
  "passed": false,
  "grade": "C",
  "score_pct": 72.0,
  "severity_counts": { "critical": 0, "high": 2, "medium": 5, "low": 11 },
  "threshold_violations": ["high"],
  "pass_threshold": 75.0,
  "severity_threshold": "high",
  "image_id": "ami-0c9d5e3f81a2b6e07",
  "sarif_url": ".../api/auditor/scan-image/7f3c9e82.../report?fmt=sarif",
  "html_report_url": ".../api/auditor/scan-image/7f3c9e82.../report"
}

The detail that will silently break your gate

A failed gate still returns HTTP 200. There is no 4xx on failure — the verdict is in the
passed field, not the status code.

That means the pattern everyone reaches for first is wrong:

# WRONG — this never fails. -f only reacts to HTTP >= 400,
# and a failed gate returns 200.
curl -sf -X POST .../api/pipeline/scan -d '...' || exit 1

You have to read the body:

# RIGHT
RESULT=$(curl -s -X POST "${BAKEX_URL}/api/pipeline/scan" \
  -H "X-API-Key: ${BAKEX_TOKEN}" \
  -H "Content-Type: application/json" \
  -d "{\"image_id\": \"${AMI_ID}\", \"pass_threshold\": 75.0, \"severity_threshold\": \"high\"}")

echo "$RESULT" | jq -r '"grade=\(.grade) score=\(.score_pct) passed=\(.passed)"'

if [ "$(echo "$RESULT" | jq -r '.passed')" != "true" ]; then
  echo "Compliance gate failed — violations: $(echo "$RESULT" | jq -c '.threshold_violations')"
  echo "Report: $(echo "$RESULT" | jq -r '.html_report_url')"
  exit 1
fi

A gate that reports failure and exits 0 is worse than no gate, because it produces a green
pipeline and the belief that something was checked.

Two thresholds, not one

passed is the AND of two independent conditions:

passed = (score_pct >= pass_threshold) AND (no findings at or above severity_threshold)

severity_threshold: "high" means any critical or high finding fails the build regardless of
score. An image can score 94 — a comfortable A — and still fail on a single critical finding. That
is the right default: scores average away the thing that gets you breached.

GitHub Actions Integration

# .github/workflows/deploy.yml

jobs:
  build-image:
    runs-on: ubuntu-latest
    outputs:
      ami_id: ${{ steps.build.outputs.ami_id }}
    steps:
      - name: Build hardened AMI
        id: build
        run: |
          AMI_ID=$(bakex build blueprints/ubuntu/22.04/cis-l1-aws.yaml --json \
            | jq -r '.artifact_id')
          echo "ami_id=${AMI_ID}" >> $GITHUB_OUTPUT

  compliance-gate:
    runs-on: ubuntu-latest
    needs: build-image
    steps:
      - name: BakeX compliance gate
        run: |
          RESULT=$(curl -s -X POST ${{ vars.BAKEX_URL }}/api/pipeline/scan \
            -H "X-API-Key: ${{ secrets.BAKEX_TOKEN }}" \
            -H "Content-Type: application/json" \
            -d "{\"image_id\": \"${{ needs.build-image.outputs.ami_id }}\",
                 \"pass_threshold\": 75.0, \"severity_threshold\": \"high\"}")

          echo "$RESULT" | jq -r '"grade=\(.grade) score=\(.score_pct)"'

          # Must check .passed — the endpoint returns 200 on failure
          if [ "$(echo "$RESULT" | jq -r '.passed')" != "true" ]; then
            echo "::error::Compliance gate failed: $(echo "$RESULT" | jq -c '.threshold_violations')"
            exit 1
          fi

      - name: Upload SARIF to code scanning
        if: always()
        run: |
          curl -s -o bakex.sarif "$(echo "$RESULT" | jq -r '.sarif_url')"
      - uses: github/codeql-action/upload-sarif@v3
        if: always()
        with:
          sarif_file: bakex.sarif

  deploy:
    runs-on: ubuntu-latest
    needs: [build-image, compliance-gate]
    steps:
      - name: Deploy to staging
        run: |
          aws autoscaling update-auto-scaling-group \
            --auto-scaling-group-name my-asg \
            --launch-template "ImageId=${{ needs.build-image.outputs.ami_id }}"

The deploy job only runs if compliance-gate passes. The AMI doesn’t reach the autoscaling group if it doesn’t meet the grade threshold.

GitLab CI Integration

# .gitlab-ci.yml

stages:
  - build
  - compliance
  - deploy

build-image:
  stage: build
  script:
    - |
      AMI_ID=$(bakex build blueprints/ubuntu/22.04/cis-l1-aws.yaml --json \
        | jq -r '.artifact_id')
      echo "AMI_ID=${AMI_ID}" >> build.env
  artifacts:
    reports:
      dotenv: build.env

compliance-gate:
  stage: compliance
  needs: [build-image]
  script:
    - |
      RESULT=$(curl -s -X POST ${BAKEX_URL}/api/pipeline/scan \
        -H "X-API-Key: ${BAKEX_TOKEN}" \
        -H "Content-Type: application/json" \
        -d "{\"image_id\": \"${AMI_ID}\", \"pass_threshold\": 75.0,
             \"severity_threshold\": \"high\"}")
      echo "$RESULT" | jq -r '"grade=\(.grade) score=\(.score_pct) passed=\(.passed)"'
      test "$(echo "$RESULT" | jq -r '.passed')" = "true"

deploy:
  stage: deploy
  needs: [build-image, compliance-gate]
  script:
    - ./deploy.sh ${AMI_ID}

What the Failed Gate Tells You

The value of the CI/CD compliance gate is not just that it blocks bad images — it’s that the failure output tells engineers what to fix.

The response carries three things an engineer can act on immediately:

$ echo "$RESULT" | jq '{grade, score_pct, threshold_violations, severity_counts}'
{
  "grade": "C",
  "score_pct": 72.0,
  "threshold_violations": ["high"],
  "severity_counts": { "critical": 0, "high": 2, "medium": 5, "low": 11 }
}

threshold_violations names the severities that broke the gate — here, two high findings, not the
score. That distinction matters: an engineer who reads “grade C” starts a broad hardening project,
while one who reads “two high findings” goes and fixes two things.

For the rule-level detail, follow sarif_url. Pushing that SARIF into GitHub code scanning (as in
the workflow above) puts each finding on the pull request diff, which is where someone will actually
read it — a link to a dashboard in a CI log is a link nobody clicks.

Thresholds by Environment

Not all environments need the same bar, and both dimensions are per-request — so the environment
distinction lives in your pipeline, not in BakeX config:

# Production — high score floor, nothing high or above
PASS=90.0 ; SEV=high

# Staging — lower floor, still no criticals
PASS=75.0 ; SEV=critical

# Development — score only, severity effectively off
PASS=60.0 ; SEV=low

curl -s -X POST "${BAKEX_URL}/api/pipeline/scan" \
  -H "X-API-Key: ${BAKEX_TOKEN}" -H "Content-Type: application/json" \
  -d "{\"image_id\": \"${AMI_ID}\", \"pass_threshold\": ${PASS}, \"severity_threshold\": \"${SEV}\"}"

Note that severity_threshold gets stricter as it goes down the list: low fails on any finding
at all, critical fails only on criticals. It reads backwards the first time. Development wanting a
permissive gate wants critical, not low.

Production Gotchas

The 200-on-failure behaviour is the whole ballgame. Repeating it because it is the one thing that
turns this page from useful to harmful if missed: check .passed. Never rely on curl -f, and never
rely on the HTTP status.

Scans take minutes, and wait: true blocks. The endpoint provisions an instance from the image
and scans it. With wait: true your CI job blocks for the duration; timeout_seconds defaults to
900. Set your CI step timeout above that, or use wait: false and poll GET /api/pipeline/scan/{job_id}.

Token rotation. The API key should rotate on the same schedule as other service credentials, and
environments should use different keys — a leaked staging key must not be able to satisfy a
production gate.

The gate needs a reachable BakeX server. This is an HTTP API, not a self-contained action: the
runner must reach the BakeX instance, and that instance needs cloud credentials for the provider
whose image it is scanning.

Key Takeaways

• A CI/CD compliance gate turns a compliance grade from a dashboard metric into a pipeline constraint — the image doesn’t deploy if it doesn’t pass
• POST /api/pipeline/scan is a single HTTP call that any CI/CD system can make — no agent, no plugin, no SDK required
• The endpoint returns 200 even when the gate fails. Parse .passed; curl -sf || exit 1 produces a green pipeline and a false sense of security
• The verdict is two-dimensional — a score floor AND a severity ceiling — so a single critical finding blocks an image that scores 94
• threshold_violations tells an engineer why it failed, which is the difference between “fix two high findings” and “start a hardening project”
• Push the sarif_url into GitHub code scanning so findings land on the pull request, not in a CI log

What’s Next

The CI/CD compliance gate closes the final gap: even if an unhardened image gets built, it can’t deploy. EP05 is the bookmark episode — this is the point where OS hardening becomes structurally enforced rather than procedurally expected.

EP06 is the series closer. For five episodes, you’ve been using BakeX as a user. What does it look like to run it yourself — extend it with a custom provider, deploy it in your own infrastructure, or contribute a blueprint back?

BakeX is Apache 2.0. EP06 is the architecture reveal, the deployment guide, and the extension points for everything the series taught.

Next: BakeX — open-source OS hardening platform for multi-cloud infrastructure

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The post The Pipeline Gate — Hardened Images as a CI/CD Build Constraint appeared first on Linuxcent.