V-285227

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. Primary name servers also make outbound connections to secondary name servers to provide zone transfers and accept inbound connection requests from clients wishing to provide a dynamic update. Primary name servers should explicitly limit zone transfers to be made only to designated secondary name servers. Because zone transfers involve the transfer of entire zones and use TCP connections, they place substantial demands on network resources relative to normal DNS queries. Errant or malicious frequent zone transfer requests on the name servers of the enterprise can overload the master zone server and result in DoS to legitimate users. Primary name servers should be configured to limit the hosts from which they will accept dynamic updates. Additionally, the number of concurrent clients, especially TCP clients, needs to be kept to a level that does not risk placing the system in a DoS state.

Check Content

Verify that Infoblox is configured to limit the number of concurrent client connections to the number of allowed dynamic update clients.

Infoblox can be configured in two ways to limit Dynamic DNS (DDNS) client updates.

For clients that support Generic Security Service Algorithm for Secret Key Transaction (GSS-TSIG):
1. From the Infoblox GUI, navigate to Data Management >> DNS >> Members tab. 
2. Review each server with the DNS service enabled, select each server, and then click "Edit".
3. Click "Toggle Advanced Mode", and select General >> GSS-TSIG tab. 
4. Verify "Enable GSS-TSIG authentication of clients" is enabled.

For clients that do not support GSS-TSIG:
1. From the Infoblox GUI, navigate to Data Management >> DNS >> Members tab. 
2. Review each server with the DNS service enabled, select each server, and then click "Edit". 
3. Select the Updates >> Basic tab. Verify that either a Named Access Control List (ACL) or Set of Access Control Entities (ACEs) are defined to limit client DDNS. 
4. When complete, click "Cancel" to exit the "Properties" screen. 

If "Enable GSS-TSIG authentication of clients" is disabled for clients supporting GSS-TSIG, or a Named ACL or set of ACEs is not defined to limit DDNS for clients without GSS-TSIG support, this is a finding.