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Table of Contents

Build System Hardening

What is build system hardening?

Build system hardening is the practice of securing the infrastructure, tools, and workflows involved in compiling, linking, and packaging software. It consists of implementing security controls that prevent unauthorized access, reduce the attack surface, and ensure the integrity of the software build process.

This process applies to CI/CD pipelines, build servers (e.g., Jenkins, GitLab, GitHub Actions), and associated systems that convert source code into deployable software.

Why is harden your build systems?

Build systems are a prime target for attackers seeking to compromise software at its source. A successful attack can inject malicious code into trusted outputs, bypass security controls, and impact thousands of downstream users.

Hardening these systems:

  • Protects against insider threats and external attackers
  • Reduces the risk of supply chain compromises (e.g., SolarWinds, XZ Utils)
  • Supports secure software delivery mandates (EO 14028, SLSA, FedRAMP)

How does it work?

Hardening involves implementing layered security controls across five key domains:

  1. Infrastructure Controls
    • Harden base OS images and build containers
    • Enforce isolation between builds (ephemeral runners, VMs)
  2. Identity & Access Management (IAM)
    • Enforce least privilege
    • Use single sign-on (SSO) and MFA
    • Audit and rotate credentials
  3. Integrity & Attestation
    • Sign and verify all build artifacts
    • Maintain build provenance logs
    • Validate SBOMs and hashes
  4. Dependency Management
    • Whitelist trusted packages and registries
    • Scan for vulnerabilities pre-build
  5. Monitoring & Response
    • Detect unauthorized script changes or file access
    • Alert on anomalous builds or pipeline behavior

Benefits

  • Improves Software Integrity: Protects against unauthorized code changes and build tampering
  • Reduces Compliance Risk: Aligns with NIST SSDF, SLSA, and FedRAMP mandates
  • Increases Customer Trust: Demonstrates secure and verifiable software release practices
  • Lowers Cost of Breaches: Reduces attack success rates and recovery expenses

Build system hardening vs

Practice

Focus Area

Key Difference

Secure Build Environments

Physical and infrastructure-level isolation

Hardening includes policies, IAM, integrity, and monitoring

CI/CD Pipeline Security

Workflow and process protection

Build system hardening focuses specifically on build components

Runtime Security

Protects deployed software

Build hardening prevents threats before deployment

Best practices for build system hardening

  • Require signed commits and enforce branch protections
  • Use cryptographic signing and hashing for all outputs
  • Block unapproved plugins and build scripts
  • Regularly audit build tool configurations and permissions
  • Monitor build server logs for anomalies

Use cases

  • Software Vendor Compliance: Meeting EO 14028 or commercial audit requirements
  • SaaS Product Integrity: Ensuring multi-tenant software is securely built and updated
  • Open-Source Project Maintenance: Protecting community contributions and releases
  • Enterprise CI/CD Governance: Securing internal and external development teams

Additional considerations

  • Map build system security controls to SLSA Levels (2–4) for progressive adoption
  • Use Infrastructure-as-Code (IaC) to enforce consistent hardening policies
  • Harden plugins and integrations, not just the core CI/CD tools
  • Avoid hardcoded secrets and credentials in build environments
  • Schedule regular penetration tests and threat simulations on the pipeline

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