Trust in Open Source: Securing the Software Supply Chain for

Every modern application is built on open-source dependencies. The average project has hundreds of transitive dependencies, each one a potential attack vector. Software supply chain security is not about trusting open source less — it is about verifying more.

The Supply Chain Attack Surface

Recent high-profile attacks:

• SolarWinds (2020): Build system compromised, malicious code injected into updates
• Codecov (2021): CI/CD tool compromised, credentials harvested
• Log4Shell (2021): Critical vulnerability in ubiquitous logging library
• xz Utils (2024): Maintainer social engineering — malicious code inserted over 2 years
• PyPI/npm malware: Thousands of typosquatting packages published monthly

The SLSA Framework

Supply chain Levels for Software Artifacts (SLSA, pronounced “salsa”) provides a maturity model:

Implementing Supply Chain Security

Step 1: Software Bill of Materials (SBOM)

Generate an SBOM for every build:

# Generate SBOM with Syft
syft dir:. -o spdx-json > sbom.spdx.json

# Or with Trivy
trivy fs . --format spdx-json --output sbom.spdx.json

# For container images
syft myapp:latest -o cyclonedx-json > sbom.cdx.json

Step 2: Vulnerability Scanning

Scan dependencies continuously:

# GitHub Actions: scan on every PR
- name: Trivy vulnerability scan
  uses: aquasecurity/trivy-action@master
  with:
    scan-type: 'fs'
    scan-ref: '.'
    format: 'sarif'
    output: 'trivy-results.sarif'
    severity: 'CRITICAL,HIGH'

Step 3: Artifact Signing

Sign all build artifacts with Sigstore:

# Sign a container image
cosign sign --key cosign.key ghcr.io/my-org/myapp:v1.0.0

# Verify a signed image
cosign verify --key cosign.pub ghcr.io/my-org/myapp:v1.0.0

Step 4: Admission Control

Only allow signed, scanned images in your cluster:

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: verify-image-signatures
spec:
  validationFailureAction: Enforce
  rules:
    - name: check-signature
      match:
        resources:
          kinds: [Pod]
      verifyImages:
        - imageReferences: ["ghcr.io/my-org/*"]
          attestors:
            - entries:
                - keys:
                    publicKeys: |-
                      -----BEGIN PUBLIC KEY-----
                      ...
                      -----END PUBLIC KEY-----

Step 5: Dependency Review

Before merging dependency updates:

# GitHub Actions: dependency review
- name: Dependency Review
  uses: actions/dependency-review-action@v4
  with:
    fail-on-severity: high
    deny-licenses: AGPL-3.0, GPL-3.0
    allow-dependencies-licenses: MIT, Apache-2.0, BSD-2-Clause, BSD-3-Clause

Kubernetes-Specific Supply Chain

• Image provenance: Require SLSA provenance attestations for all images
• Base image management: Maintain curated, scanned base images
• Helm chart verification: Sign and verify Helm charts
• Operator trust: Verify operator images from OperatorHub

Related Reading

• Container Security Scanning with Trivy
• Trivy vs Grype Comparison
• Kyverno CNCF Graduation