Securing your CI/CD pipeline: practical patterns for supply chain defense

The software you build relies on a chain of dependencies, tools, and processes—your supply chain. If any link is weak, attackers can inject malicious code, tamper with builds, or compromise your deployed applications. This isn’t theoretical; real-world attacks like SolarWinds demonstrate the critical need to defend your CI/CD pipeline.

Securing your CI/CD isn’t a one-time task, but a continuous effort applying security principles throughout the automation workflow. Let’s explore practical patterns you can adopt.

Guard your source code

Your source code is the foundation. Protect it. Use version control systems (like Git) with branch protection rules requiring reviews before merging code into main branches. Enable multi-factor authentication (MFA) for all users and integrate with identity providers.

Consider signing your commits. Git supports GPG signing. This verifies the identity of the committer, making it harder for an attacker to inject code masquerading as a trusted team member. Why sign? It adds non-repudiation; you can be more confident who wrote which line of code.

Manage dependencies carefully

Most applications use open-source libraries. These are frequent targets for supply chain attacks (e.g., typosquatting, malicious versions). Don’t pull dependencies blindly.

Pin your dependency versions explicitly. Avoid using floating versions (latest, *) that can change unexpectedly. Use lock files (package-lock.json, yarn.lock, Gemfile.lock, Pipfile.lock) and commit them. Why lock? It ensures reproducible builds and prevents unexpected malicious updates.

Scan your dependencies for known vulnerabilities using tools like OWASP Dependency Check, Snyk, or Renovate. Integrate scanning into your pull request process. Why scan? It proactively identifies risky components before they enter your codebase.

Consider using private package registries or proxying public ones. This gives you more control and allows pre-scanning or policy enforcement on dependencies entering your environment.

Harden your build environment

The environment where your code is built is a prime target. Treat build agents/runners as ephemeral and disposable. Spin them up for a single job and tear them down. Why ephemeral? It limits the window of opportunity for an attacker to persist on a build machine.

Apply the principle of least privilege to build agent permissions. They should only access what’s strictly necessary for the build. Avoid giving them broad network access or permissions to sensitive systems.

Use minimal, hardened container images for builds. Reduce the attack surface by including only essential tools.

Hermetic builds are ideal but complex. They ensure builds only use source code and dependencies explicitly defined, ignoring anything else in the environment. Bazel is an example of a tool supporting hermeticity. Why hermetic? It prevents environmental variations or injected artifacts from affecting the build output.

Secure your artifacts and provenance

The output of your build—your container images, binaries, packages—must be protected. Sign your build artifacts. Sigstore is a project providing tools (like Cosign for containers) to sign artifacts and store signatures publicly in a transparency log. Why sign artifacts? Consumers of your artifact can verify it hasn’t been tampered with since it was built by you.

Generate and store build provenance. This is metadata detailing how an artifact was built: source code version, build environment, dependencies used. Standards like SLSA (Supply Chain Levels for Software Artifacts) define levels of provenance.

Store artifacts in secure, access-controlled registries.

Protect your secrets

CI/CD pipelines need access to secrets (API keys, credentials). Do not hardcode secrets in code or configuration files. Use a dedicated secrets management system (like HashiCorp Vault, AWS Secrets Manager, Kubernetes Secrets). Why use a manager? It centralizes secret storage, encrypts secrets at rest and in transit, and allows fine-grained access control and auditing.

Inject secrets into the build or deployment process at runtime, exposed only as environment variables or files available briefly to the specific job that needs them.

Monitor and audit everything

Implement comprehensive logging and monitoring across your CI/CD pipeline. Track code changes, build executions, dependency updates, security scan results, and deployment events.

Analyze logs for suspicious activity: builds running at unusual times, unexpected changes to build scripts, unauthorized access attempts. Integrate with a SIEM (Security Information and Event Management) system.

Regularly audit pipeline configurations, access controls, and security policies.

Put patterns into practice

Implementing these patterns requires effort. Start small. Prioritize based on your risk assessment. Protecting your CI/CD pipeline is fundamental to delivering trustworthy software. By adopting these practical defense mechanisms, you significantly raise the bar for attackers targeting your software supply chain.