2.1.4.1 Ensure ntp access control is configured
Audit#
IF ntp is in use on the system, run the following command to verify the restrict lines:
# grep -P -- '^\h*restrict\h+((-4\h+)?|-6\h+)default\h+(?:[^#\n\r]+\h+)*(?!(?:\2|\3|\4|\5))(\h*\bkod\b\h*|\h*\bnomodify\b\h*|\h*\bnotrap\b\h*\h*\bnopeer\b\h*|\h*\bnoquery\b\h*)\h+(?:[^#\n\r]+\h+)*(?!(?:\1|\3|\4|\5))(\h*\bkod\b\h*|\h*\bnomodify\b\h*|\h*\bnotrap\b\h*|\h*\bnopeer\b\h* \h*\bnoquery\b\h*)\h+(?:[^#\n\r]+\h+)*(?!(?:\1|\2|\4|\5))(\h*\bkod\b\h*|\h*\bnomodify\b\h*|\h*\bnotrap\b\h*|\h*\bnopeer\b\h*|\h*\bnoquery\b\h*)\h+(?:[^#\n\r]+\h+)*(?!(?:\1|\2|\3|\5))(\h*\bkod\b\h*|\h*\bnomodify\b\h*|\h*\bnotrap\b\h*|\h*\bnopeer\b\h*|\h*\bnoquery\b\h*)\h+(?:[^#\n\r]+\h+)*(?!(?:\1|\2|\3|\4))(\h*\bkod\b\h*|\h*\bnomodify\b\h*|\h*\bnotrap\b\h*|\h*\bnopeer\b\h*|\h*\bnoquery\b\h*)\h*(?:\h+\H+\h*)*(?:\h+#.*)?$' /etc/ntp.conf
Output should be similar to:
restrict -4 default kod notrap nomodify nopeer noquery
restrict -6 default kod notrap nomodify nopeer noquery
Verify that the output includes two lines, and both lines include: default, kod, nomodify, notrap, nopeer and noquery.
Note: The -4 in the first line is optional, options after default may appear in any order, and additional options may exist.
Remediation#
Add or edit restrict lines in /etc/ntp.conf to match the following:
restrict -4 default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
OR
If another time synchronization service is in use on the system, run the following command to remove ntp from the system:
Default Value: