Title

For zones split between the external and internal sides of a network, the RRs for the external hosts must be separate from the RRs for the internal hosts. (Cat II impact)

Discussion

Authoritative name servers for an enterprise may be configured to receive requests from both external and internal clients. External clients need to receive RRs that pertain only to public services (public Web server, mail server, etc.) Internal clients need to receive RRs pertaining to public services as well as internal hosts. The zone information that serves the RRs on both the inside and the outside of a firewall should be split into different physical files for these two types of clients (one file for external clients and one file for internal clients).

Check Content

Review the Resource Records (RRs) of each zone which is split between external and internal networks. For those internal hosts which are intended to be accessed by both internal and external users, a different RR should be listed on each of the internal and external name servers, with IP addresses reflective of the external or internal network. Traffic destined for those internal hosts will resolve to the IP address in the external name server and then should be NAT'd through the perimeter firewall. Verify the RRs in the internal name server are not also listed in the external name server. If there are RRs in the internal name server for hosts also listed in the external name server, and the IP to which it resolves is on the external network, this is a finding. Verify the RRs in the external name server are not also listed in the internal name server. If there are RRs in the external name server for hosts also listed in the internal name server, and the IP to which it resolves is on the internal network, this is a finding.

Fix Text

Remove any RRs listed in the internal name server configuration which resolve for external hosts and remove any RRs listed in the external name server configuration which resolve to internal hosts. For hosts intended to be accessed by both internal and external clients, configure unique IP addresses in each of the internal and external name servers, respective to their location. The perimeter firewall, or other routing device, should handle the Network Address Translation to the true IP address of the destination.

Additional Identifiers

Rule ID: SV-205236r961863_rule

Vulnerability ID: V-205236

Group Title: SRG-APP-000516

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.