AWS Lambda Security: Function Hardening and Runtime Protection

Part of the Cybersecurity Skills Guide — This article is one deep-dive in our complete guide series.

By HADESS Team | February 28, 2026 | Updated: February 28, 2026 | 5 min read

Lambda shifts the security model compared to traditional compute. You do not manage the operating system, the runtime environment, or the hypervisor. But you still own the application code, the IAM permissions, the network configuration, and the dependencies bundled with your function. These are the areas where Lambda security goes wrong.

IAM Roles: One Per Function

Every Lambda function needs its own execution role with the minimum permissions required. This is where teams cut corners most often. A shared role across twenty functions means every function has the combined permissions of all twenty — and an attacker who compromises any one of them gets everything.

Use resource-level permissions whenever the service supports it. Instead of s3:GetObject on *, scope it to the specific bucket and prefix your function needs. Add conditions like aws:SourceAccount to prevent confused deputy attacks.

Review what your function actually calls using IAM Access Analyzer’s policy generation. Deploy with broad permissions in a dev environment, let Access Analyzer observe the API calls, then generate a scoped policy for production.

VPC Configuration

Lambda functions do not run in your VPC by default. They run in an AWS-managed VPC with internet access. If your function needs to access resources in your VPC (databases, caches, internal APIs), attach it to your VPC’s private subnets.

Once a Lambda is in your VPC, it loses direct internet access. If it needs to call external APIs or AWS services, route through a NAT gateway or use VPC endpoints. VPC endpoints are preferable for AWS services because traffic stays on the AWS network and you can apply endpoint policies for additional access control.

Do not put Lambda functions in a VPC unless they need to talk to VPC resources. VPC attachment adds cold start latency and requires managing ENIs in your subnets.

Dependencies and Runtime

Lambda functions are only as secure as their dependencies. Use a lock file (package-lock.json, requirements.txt with pinned versions, go.sum) and scan dependencies with Inspector or a third-party SCA tool in your CI pipeline.

Keep your runtime current. AWS deprecates older runtimes and stops applying security patches. Enable Lambda runtime management controls to apply patches automatically. Use Lambda layers for shared dependencies so you can update a library in one place.

Environment Variables and Secrets

Environment variables are stored in the function configuration and visible to anyone with lambda:GetFunction permission. Encrypt sensitive environment variables with a KMS key, and better yet, retrieve secrets at runtime from Secrets Manager or Parameter Store using the AWS Parameters and Secrets Lambda Extension. This caches secrets locally and handles rotation without redeploying the function.

Event Injection

Lambda functions triggered by API Gateway, S3 events, SQS messages, or DynamoDB streams receive untrusted input. Validate and sanitize event data the same way you would in a web application. SQL injection, command injection, and path traversal attacks all apply to Lambda functions that process user-controlled input.

Log event payloads (excluding sensitive fields) for forensic analysis. Use structured logging with a correlation ID to trace events through invocation chains.

Next Steps

• Explore serverless and application security topics in the skills library
• Take a skills assessment to benchmark your serverless security knowledge
• Use the coaching tool to plan your path into cloud-native security

Related Guides in This Series

• Active Directory Security: Attack Paths and Hardening — HADESS | 2026
• AWS ALB Security: TLS, Authentication, and Access Controls — HADESS | 2026
• AWS CloudTrail: Log Analysis and Security Monitoring — HADESS | 2026

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