AWS Lambda Function Without Appropriate Network Access and Isolation


AWS Lambda allows you to run code without provisioning servers. While Lambda functions can operate without VPC connectivity, integrating them with a VPC ensures better network isolation and security. Without appropriate network access and isolation, a Lambda function might be exposed to unintended network access, potential data exfiltration, or unauthorized access to internal resources. Ensuring that Lambda functions have only the necessary network permissions and are properly isolated within a VPC is crucial for security best practices.


1. Configure Lambda for VPC and Restrict Network Access:

AWS Management Console:
  • Navigate to the Lambda service in the AWS Console.
  • Choose the Lambda function you want to update.
  • Under the Configuration tab, go to the VPC section.
  • Assign the Lambda function to a specific VPC, Subnets, and Security Groups.
    • Ensure the chosen subnets provide the required access to resources (like databases or cache) and have no direct internet access unless necessary.
    • The Security Groups should have minimal inbound/outbound rules, granting only the necessary permissions.
  • Save your changes.

To update a Lambda function's VPC configuration:

aws lambda update-function-configuration --function-name YOUR_LAMBDA_FUNCTION_NAME --vpc-config SubnetIds=subnet-0123456789abcdef0,subnet-0123456789abcdef1,SecurityGroupIds=sg-0123456789abcdef0

Replace the subnet and security group IDs with your specific IDs.


Using Terraform to configure the Lambda function for VPC:

resource "aws_lambda_function" "example" {
  # ... other Lambda configurations ...

  vpc_config {
    subnet_ids         = [,]
    security_group_ids = []

Ensure that the associated Security Groups and NACLs for the VPC and subnets are configured to allow only necessary traffic.


Always configure Lambda functions with appropriate network access and isolation, especially when they interact with sensitive internal resources or databases. Associating them with a VPC and carefully crafted security groups ensures network isolation and reduces potential risks. Periodically review the network configurations and ensure that security groups and NACLs align with the principle of least privilege, granting only the permissions necessary for the function's operation.