V-285278

Discussion

The only protection approach for content control of DNS zone files is the use of a zone file integrity checker. The effectiveness of integrity checking using a zone file integrity checker depends upon the database of constraints built into the checker. The deployment process consists of developing these constraints with the right logic, and the only determinant of the truth value of these logical predicates is the parameter values for certain key fields in the format of various RRTypes. The serial number in the SOA RDATA is used to indicate to secondary name servers that a change to the zone has occurred and a zone transfer should be performed. It should always be increased whenever a change is made to the zone data. DNS NOTIFY must be enabled on the master authoritative name server.

Check Content

Review DNS zone data to validate the SOA on all authoritative DNS service members. Remote DNS service members that do not have the same serial number as the primary DNS service member may have network issues or misconfiguration blocking updates. 

Use either the "nslookup" or "dig" utility to review the serial number returned from each DNS service member. 

1. Open a command line/terminal.
2. Query the Primary Name Server using either dig or nslookup 'dig @<Primary_IP> <ZONE> SOA' or nslookup 'nslookup -type=SOA <ZONE> <PRIMARY_IP>'
With dig, the SOA serial will be the first number after the zone, with nslookup, it will be listed as serial.
3. Perform step 2 to query all other name servers for that zone.

If any serial numbers for the same zone do not match, this is a finding.