Title

The BIND 9.x secondary name server must limit the number of zones requested from a single master name server. (Cat II impact)

Discussion

Limiting the number of concurrent sessions reduces the risk of Denial of Service (DoS) to the DNS implementation. Name servers do not have direct user connections but accept client connections for queries. Original restriction on client connections should be high enough to prevent a self-imposed denial of service, after which the connections are monitored and fine-tuned to best meet the organization's specific requirements.

Check Content

If this is not a secondary name server, this requirement is Not Applicable. Verify that the secondary name server is configured to limit the number of zones requested from a single master name server. Inspect the "named.conf" file for the following: options { transfers-per-ns 2; }; If the "options" statement does not contain a "transfers-per-ns" sub statement, this is a finding.

Fix Text

Edit the "named.conf" file. Add the "transfers-per-ns" sub statement to the "options" statement block. The value of the "transfers-per-ns" option can be increased to a value greater than two based on organizational requirements needed to support DNS operations. Restart the BIND 9.x process.

Additional Identifiers

Rule ID: SV-207549r879511_rule

Vulnerability ID: V-207549

Group Title: SRG-APP-000001-DNS-000001

Expert Comments

CCIs tied to check.

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