Do Not Define a Static Source Port

MediumLevel 1Automatedbind

Description

BIND can be configured to always use the same source port when communicating with other DNS servers. This capability is made possible through the query-source port option, and the query-source-v6 port option. It is recommended that the source port be omitted if the query-source option is used, or that the port be specified as a *, so that the port will not be a static port ... The audit fails when any query-source or query-source-v6 statement sets a fixed port (port * / port 0 is allowed). The audit parses the effective configuration printed by named-checkconf -p (all include files resolved) from /etc/named.conf (RHEL; chroot /var/named/chroot is detected) or /etc/bind/named.conf (Debian/Ubuntu).

How it is checked

Audit method: Shell command

shell

if [ -f /var/named/chroot/etc/named.conf ]; then out=$(named-checkconf -t /var/named/chroot -p /etc/named.conf 2>/dev/null) || exit 1
else conf=/etc/named.conf; [ -f "$conf" ] || conf=/etc/bind/named.conf
  out=$(named-checkconf -p "$conf" 2>/dev/null) || exit 1; fi
flat=$(printf '%s\n' "$out" | tr '\t\n' '  ' | tr -s ' ')
opts=$(printf '%s\n' "$out" | awk '/^options[ \t]*\{/{f=1} f{print} f&&/^\};/{exit}' | tr '\t\n' '  ' | tr -s ' ')
bad=$(printf '%s\n' "$flat" | grep -Eo 'query-source(-v6)? [^;]*;' | grep -E ' port [1-9][0-9]*')
[ -z "$bad" ] && echo compliant || { echo 'static query source port:'; printf '%s\n' "$bad"; }

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Either remove the port specification from the query-source or the query-source-v6 option or use an * for the port number.

Properties

Operating systems: Any
Tags: binddnsdnssec
Reference: CIS ISC BIND DNS Server 9.11 Benchmark v1.0.0 - 7.1 Do Not Define a Static Source Port

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target bind