What are the best practices for serverless security?

What are the best practices for serverless security?

Serverless security focuses on securing code, configurations, and dependencies while minimizing risks from third-party services. Unlike traditional architectures, serverless shifts infrastructure management to cloud providers, but developers remain responsible for securing their functions, data, and access controls. Key practices include strict permission policies, dependency management, and continuous monitoring.

First, enforce the principle of least privilege for permissions. Serverless functions often interact with databases, storage, or APIs, so granting excessive access increases attack surfaces. For example, an AWS Lambda function writing to an S3 bucket should only have write permissions to that specific bucket—not full S3 access. Use tools like AWS IAM Roles or Azure Managed Identities to define granular permissions. Avoid wildcard policies (e.g., "s3:*") and audit roles regularly to remove unused privileges. Additionally, secure environment variables by encrypting secrets (e.g., API keys) with services like AWS Secrets Manager instead of hardcoding them in function code.

Second, manage dependencies and code vulnerabilities. Serverless functions rely on third-party libraries, which can introduce security flaws. Use tools like Snyk or Dependabot to scan dependencies for known vulnerabilities. For instance, a Node.js function using an outdated lodash version with a prototype pollution flaw could be exploited if not patched. Also, minimize function code size to reduce attack surfaces—avoid unnecessary packages and implement input validation to prevent injection attacks. For example, sanitize user inputs in a REST API handler to block SQLi or XSS attempts.

Finally, implement logging and monitoring. Serverless architectures are distributed, making tracing threats harder. Centralize logs using services like AWS CloudWatch or Datadog to detect anomalies, such as unexpected spikes in function invocations or unauthorized access attempts. Set up alerts for suspicious activities, like repeated failed authentication in an Auth0-protected API. Conduct regular penetration tests and use tools like AWS GuardDuty to identify misconfigurations. For example, a misconfigured public API Gateway endpoint could expose sensitive data, so automated scans can flag such issues early.

By combining strict access controls, dependency hygiene, and proactive monitoring, developers can mitigate risks in serverless environments effectively.