What Is Serverless Security

Serverless security is the practice of addressing security risks specific to serverless computing environments such as AWS Lambda, Azure Functions, and Google Cloud Functions.

In serverless environments, OS and runtime management is delegated to the provider, so the shared responsibility model shifts. While the burden of OS patching and server hardening is eliminated, application-layer security - function code, permissions, dependencies, and input validation - becomes the customer's primary responsibility.

Serverless-Specific Attack Surfaces

Serverless environments have different attack surfaces than traditional server-based applications.

Event Injection: Lambda functions are invoked from diverse event sources such as API Gateway, S3, SQS, and DynamoDB Streams. Input from each event source must not be trusted - always validate and sanitize within the function. For example, an S3 object key containing special characters could trigger path traversal if used directly in file operations
Overly Broad Permissions: Assigning a single IAM role with broad permissions to all functions means that if one function is compromised, the attacker gains access to all resources. Design the minimum required permissions for each function individually
Dependency Vulnerabilities: Third-party libraries included in function packages may contain known vulnerabilities. Since serverless functions are deployed frequently, dependency scanning must be integrated into the CI/CD pipeline
Execution Environment Reuse: Lambda reuses execution environments (warm starts) for performance. Data stored in global variables or the /tmp directory from a previous invocation may persist. Never store sensitive information in these locations

Serverless Security Best Practices

Practical measures to strengthen serverless environment security.

Per-Function Least-Privilege IAM Roles: Do not share a common IAM role across all functions. Define policies per function using AWS SAM or Serverless Framework templates
Input Validation: Validate event data schema, data types, and value ranges at the function entry point. Use API Gateway request validators and Lambda Powertools for structured validation
Dependency Management: Regularly update dependencies and integrate vulnerability scanning (Snyk, Dependabot) into CI/CD. Pin dependency versions and verify integrity with lock files
Environment Variable Encryption: Encrypt Lambda environment variables with KMS. For highly sensitive information, retrieve directly from Secrets Manager at runtime rather than using environment variables

Monitoring and Incident Response

Monitoring serverless environments requires a different approach than traditional server monitoring.

Function-Level Logging: Output structured logs to CloudWatch Logs, making request IDs, execution times, and error information traceable. Filter logs to ensure secrets and personal information are not included
Anomaly Detection: Detect anomalies such as unusual increases in function invocation count, execution time spikes, and error rate increases. CloudWatch Alarms and third-party tools (Datadog, Lumigo) provide serverless-specific monitoring
Distributed Tracing: Use AWS X-Ray to visualize call chains across multiple functions and services. This enables quick identification of performance bottlenecks and error origins

To learn more about this topic, see API Security Basics: Protecting the Backend of Web Services.

Common Misconceptions

Serverless means no servers, so there are no security concerns: Even in serverless environments, application-layer security risks exist, including function code vulnerabilities, IAM misconfigurations, dependency vulnerabilities, and malicious input from event sources. While OS management burden is reduced, security responsibility does not disappear.
Lambda functions execute for such short periods that there is no time to be attacked: Even with short execution times, a single invocation can steal sensitive data or misuse resources. In environments where functions are repeatedly invoked, attackers can try as many times as they want. Short execution time is not a security guarantee.

Serverless Security