AWS Lambda Security Best Practices
Tags: aws, lambda, security, cybersecurity
Published: 2022-12-18 15:14:37

AWS Lambda is a powerful and popular serverless computing platform that allows you to run code without the need to provision or manage servers. However, like any cloud service, it's important to ensure that your Lambda functions are secure and follow best practices to protect against potential vulnerabilities.

Here are some key security best practices for AWS Lambda:

**Use tight IAM Roles and Least Privilege Permissions**
To secure an AWS Lambda function using IAM (Identity and Access Management), you can follow these steps:

- Navigate to the IAM console in the AWS Management Console.

- Create an IAM policy that defines the permissions you want to grant to the function. For example, you might want to allow the function to access certain resources in an Amazon S3 bucket, or to write logs to Amazon CloudWatch. Keep it tight and exercise least privilege - e.g. only a single S3 bucket not all S3 buckets! Remember the Capital One breach ;)

- Create an IAM role that you will attach to the function. This role should be based on the policy you created in step 2.

- In the AWS Lambda console, open the function that you want to secure.

Under the "Execution role" section, select the IAM role you created in step 3. This will allow the function to assume the role and use the permissions defined in the associated policy when it is executed.

Fine-grained access control in AWS Identity and Access Management (IAM) is a way to grant specific permissions to users or processes in your AWS account. This allows you to limit access to certain resources or actions in your AWS environment, helping to secure your resources and prevent unauthorized access or modifications.

Here is an example of an IAM policy that uses fine-grained access control to allow a user to perform only specific actions on a specific resource:

`{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowReadOnlyAccessToS3Bucket",
            "Effect": "Allow",
            "Action": [
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource": [
                "arn:aws:s3:::my-bucket",
                "arn:aws:s3:::my-bucket/*"
            ]
        }
    ]
}`
In this example, the policy allows the user to perform the s3:ListBucket and s3:GetObject actions on the my-bucket Amazon S3 bucket and all of its objects. This allows the user to list the contents of the bucket and retrieve objects from it, but does not allow them to perform any other actions (such as deleting objects or modifying bucket permissions).

You can use fine-grained access control in IAM policies to limit access to specific AWS resources or actions in your account, helping to improve the security of your AWS environment.

Save your changes.

Note that you can also use resource-based policies to control access to your Lambda functions. These policies can be attached directly to the function, and define which AWS accounts or IAM users have permission to invoke the function.


**API Gateway**
Using an API Gateway with AWS Lambda can provide better security in a number of ways:

Access control: The API Gateway can enforce fine-grained access control to your backend resources. For example, you can use IAM policies to specify which users or groups have access to which API methods and resources.

Throttling: The API Gateway allows you to set limits on the number of requests that can be made to your backend resources, helping to prevent Denial of Service (DoS) attacks.

Encryption: The API Gateway can automatically encrypt the data transmitted between it and the client using SSL/TLS.

Monitoring: The API Gateway provides detailed logs and metrics on all API traffic, allowing you to monitor for unusual activity or unauthorized access attempts.

To use the API Gateway with AWS Lambda, you can create a new API Gateway resource and then create a new Lambda function to handle the requests. You can then map the incoming HTTP requests to the appropriate Lambda function using the API Gateway's integration settings.

For more information, you can refer to the AWS documentation on Using an API Gateway with AWS Lambda @ https://docs.aws.amazon.com/lambda/latest/dg/services-apigateway.html

**Use CORS on Lambda URLs**
Cross-Origin Resource Sharing (CORS) is a security feature that allows a web browser to make requests to a server from a different origin (domain, protocol, or port) than the one that served the web page. Enabling CORS in an AWS Lambda function is done by specifying the appropriate headers in the response from the function.

Here's an example of how you can enable CORS in an AWS Lambda function written in Node.js:

`exports.handler = async (event) => {
  // Your code goes here

  const response = {
    statusCode: 200,
    headers: {
      "Access-Control-Allow-Origin": "*",  // Allow requests from any origin
      "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE",  // Allow these HTTP methods
      "Access-Control-Allow-Headers": "Content-Type"  // Allow these HTTP headers
    },
    body: JSON.stringify({
      message: 'Hello from Lambda!'
    })
  };
  return response;
};`

In this example, the Access-Control-Allow-Origin header allows requests from any origin, the Access-Control-Allow-Methods header allows GET, POST, PUT, and DELETE methods, and the Access-Control-Allow-Headers header allows the Content-Type header. You can customize these headers to fit your specific needs.

Note that CORS is only one aspect of security. You should also consider implementing other security measures, such as authentication and authorization, to further protect your application.

For more see:
- https://docs.aws.amazon.com/lambda/latest/dg/lambda-security.html