Lambda permission principal is wildcard

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Metadata

Id: e08ed7eb-f3ef-494d-9d22-2e3db756a347

Cloud Provider: AWS

Platform: Terraform

Severity: Medium

Category: Access Control

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Description

Lambda function permissions should not define the principal attribute with a wildcard (*) value. Using a wildcard as the principal allows any AWS account or service to invoke the Lambda function, significantly increasing the risk of unauthorized access or unintentional exposure. Instead, the principal should be set to the specific AWS service or account that requires access, such as events.amazonaws.com, to enforce strict access controls and limit potential abuse.

Compliant Code Examples

resource "aws_lambda_permission" "negative1" {
  statement_id  = "AllowExecutionFromCloudWatch"
  action        = "lambda:InvokeFunction"
  function_name = aws_lambda_function.test_lambda.function_name
  principal     = "events.amazonaws.com"
  source_arn    = "arn:aws:events:eu-west-1:111122223333:rule/RunDaily"
  qualifier     = aws_lambda_alias.test_alias.name
}

Non-Compliant Code Examples

resource "aws_lambda_permission" "positive1" {
  statement_id  = "AllowExecutionFromCloudWatch"
  action        = "lambda:InvokeFunction"
  function_name = aws_lambda_function.test_lambda.function_name
  principal     = "*"
  source_arn    = "arn:aws:events:eu-west-1:111122223333:rule/RunDaily"
  qualifier     = aws_lambda_alias.test_alias.name
}