AWS SDK for .NET works with Amazon Web Services to help build scalable solutions with Amazon S3, Amazon DynamoDB, Amazon Glacier, and more. From versions 4.0.0 to before 4.0.3.3, Customer applications could be configured to improperly route AWS API calls to non-existent or non-AWS hosts. This notification is related to the use of specific values for the region input field when calling AWS services. An actor with access to the environment in which the SDK is used could set the region input field to an invalid value. This issue has been patched in version 4.0.3.3.

AWS SDK for .NET V4 adopted defense in depth enhancement for region parameter value