Title

A BIND 9.x server validity period for the RRSIGs covering a zones DNSKEY RRSet must be no less than two days and no more than one week. (Cat II impact)

Discussion

The best way for a zone administrator to minimize the impact of a key compromise is by limiting the validity period of RRSIGs in the zone and in the parent zone. This strategy limits the time during which an attacker can take advantage of a compromised key to forge responses. An attacker that has compromised a zone signing key (ZSK) can use that key only during the key signing key's (KSK's) signature validity interval. An attacker that has compromised a KSK can use that key for only as long as the signature interval of the RRSIG covering the DS RR in the delegating parent. These validity periods should be short, which will require frequent re-signing.

Check Content

With the assistance of the DNS administrator, identify the RRSIGs that cover the DNSKEY resource record set for each zone. Each record will list an expiration and inception date, the difference of which will provide the validity period. The dates are listed in the following format: YYYYMMDDHHMMSS For each RRSIG identified, verify that the validity period is no less than two days and is no longer than seven days. If the validity period is outside of the specified range, this is a finding.

Fix Text

Re-sign each zone that is outside of the validity period. Restart the BIND 9.x process.

Additional Identifiers

Rule ID: SV-272389r1068006_rule

Vulnerability ID: V-272389

Group Title: SRG-APP-000516-DNS-000078

Expert Comments

CCIs tied to check.

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