Cis Bind9 V301 6 2

CIS 6.2 — Hide Nameserver ID

Profile Applicability

• Level 1 - Authoritative Name Server
• Level 1 - Caching Only Name Server

Description

The server-id option provides a server identifier that will be returned in response to an NSID query. An NSID query is described in RFC-5001, and is a method to identify servers in an environment where there are multiple DNS servers sharing the same IP address. With the use of load balancing and other IP sharing mechanisms, it can become difficult to discern exactly which name server is responding to a particular query. NSID allows a name server to respond with identifying information. The server-id option should be disabled with a value of none.

Rationale

Enabling the NSID option may allow external parties to obtain information about the configuration and architecture of the DNS server. If it is found to be necessary to enable this service, then the identifying information should be generic. You should not use the server's geographic location, internal IP address or any other privileged information.

Impact

None noted.

Audit Procedure

Use the dig command below to send an NSID query, on the built-in zone id.server, for a chaos class TXT record. There should not be any output for a compliant configuration.

$ dig @ns2.cisecurity.local id.server chaos txt | grep '^id.server.' | grep TXT

An example of a non-compliant response to an NSID query is shown below.

$ dig @ns1.cisecurity.local id.server chaos txt | grep '^id.server.' | grep TXT
id.server.          0       CH      TXT     "cpe-172.lima.ny.us.local"

Remediation

To explicitly disable NSID support, add or modify the server-id option in the global BIND options with a value of none as shown below.

server-id none;

Default Value

NSID is disabled by default.

References

1. https://tools.ietf.org/html/rfc5001

CIS Controls

MITRE ATT&CK Mappings

Profile

• Level 1 - Authoritative Name Server
• Level 1 - Caching Only Name Server