NS record in Route53 for my sub domain with some value which is not DNS name

It is possible for a NS record to be created for a subdomain without the administrator's knowledge if the parent domain has been configured to allow this. In Route 53, the administrator of the parent domain can create a delegation set, which consists of a group of NS records that can be used by subdomains. When a subdomain is created, it can be associated with the delegation set, allowing it to use the NS records in the set. This allows the subdomain to use its own set of name servers, independent of the parent domain.

It is also possible that the NS record for the subdomain was created by someone else with access to the parent domain's hosted zone. In this case, the administrator may not have been aware of the creation of the NS record.

If you want to see who created an NS record in Amazon Route 53, you can view the record's history in the Amazon Route 53 console. To do this, follow these steps:

Sign in to the AWS Management Console and open the Amazon Route 53 console.

In the navigation pane, choose Hosted zones.

Select the hosted zone that contains the NS record you want to view.

In the record sets list, choose the NS record you want to view.

In the record set details pane, choose the History tab.

The history of the NS record will be displayed, including the date and time when the record was created or modified, and the AWS Identity and Access Management (IAM) user or role that performed the action.

Keep in mind that this information is only available for up to 90 days after the record was created or modified. After that time, the history for the record will be deleted and cannot be recovered.

Additionally, if you want to see who has permission to create or modify DNS records in your hosted zone, you can view the IAM policies that are attached to your hosted zone. To do this, follow these steps:

Sign in to the AWS Management Console and open the Amazon Route 53 console.

In the navigation pane, choose Hosted zones.

Select the hosted zone that you want to view the permissions for.

In the details pane, choose the Permissions tab.

The IAM policies that are attached to your hosted zone will be listed, along with the actions that are allowed by each policy.

You can use this information to determine who has the ability to create or modify DNS records in your hosted zone, and to make any necessary changes to those permissions.