Description:
Cross-origin resource sharing (CORS) is a mechanism that allows a web page to request resources from a different origin. This can be useful for loading scripts, images, or other content from a different domain. However, it can also be used to exploit security vulnerabilities.

This policy ensures that Lambda function URL CORS configurations are checked to prevent unauthorized access to the function.

Rationale:
CORS configurations can be used to restrict access to a Lambda function to specific domains or origins. This helps to protect the function from unauthorized access.

Impact:
If CORS configurations are not checked, then unauthorized users may be able to access the Lambda function. This could lead to data breaches, loss of functionality, or other security vulnerabilities.

Default Value:
AWS will recommend that CORS configurations are enabled for all Lambda functions. This means that only requests from specific domains or origins will be able to access the function.

Pre-requisites:

  • Access to the AWS Lambda console or the AWS CLI.
  • Knowledge of CORS configurations.

Remediation Steps:

  1. Go to the AWS Lambda console or the AWS CLI.
  2. Select the Lambda function that you want to check the CORS configurations for.
  3. Click on the "Configuration" tab.
  4. Under the "CORS" section, check the "Enable CORS" checkbox.
  5. Enter the domains or origins that you want to allow to access the function.
  6. Click on the "Save" button.

Test Plan:

  1. Make a request to the Lambda function from a domain or origin that is not listed in the CORS configurations.
  2. If the request is successful, then the CORS configurations are not set correctly.
  3. If the request is denied, then the CORS configurations are set correctly.

Implementation Plan:

  1. Follow the remediation steps to enable CORS for the Lambda function.
  2. Test the CORS configurations to make sure that they are working correctly.

AWS CLI Process:

To enable CORS for a Lambda function using the AWS CLI, you can use the following command:

aws lambda update-function-configuration --function-name <function-name> --cors-configuration "'*'"

Using AWS GUI:

To enable CORS for a Lambda function using the AWS GUI, you can follow these steps:

  1. Go to the AWS Lambda console.
  2. Select the Lambda function that you want to enable CORS for.
  3. Click on the "Configuration" tab.
  4. Under the "CORS" section, check the "Enable CORS" checkbox.
  5. Enter the domains or origins that you want to allow to access the function.
  6. Click on the "Save" button.

Backout Plan:

To backout the changes to the CORS configurations, you can follow these steps:

  1. Go to the AWS Lambda console or the AWS CLI.
  2. Select the Lambda function that you want to disable CORS for.
  3. Click on the "Configuration" tab.
  4. Under the "CORS" section, uncheck the "Enable CORS" checkbox.
  5. Click on the "Save" button.

Note:

  • This policy is only applicable to Lambda functions that have a public URL.
  • If you are not sure whether a Lambda function has a public URL, you can check the "Configuration" tab in the AWS Lambda console.

Reference: