Set Default ip6tables Policy for Incoming Packets
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Description
To set the default policy to DROP (instead of ACCEPT) for
the built-in INPUT chain which processes incoming packets,
add or correct the following line in
/etc/sysconfig/ip6tables
:
If changes were required, reload the ip6tables rules:
$ sudo service ip6tables reload
Rationale
In ip6tables
, the default policy is applied only after all
the applicable rules in the table are examined for a match. Setting the
default policy to DROP
implements proper design for a firewall, i.e.
any packets which are not explicitly permitted should not be
accepted.
Shell script
The following script can be run on the host to remediate the issue.
#!/bin/bash
# Remediation is applicable only in certain platforms
if ( ! ( dpkg-query --show --showformat='${db:Status-Status}\n' 'nftables' 2>/dev/null | grep -q installed ) && ! ( dpkg-query --show --showformat='${db:Status-Status}\n' 'ufw' 2>/dev/null | grep -q installed ) && dpkg-query --show --showformat='${db:Status-Status}\n' 'iptables' 2>/dev/null | grep -q installed ); then
sed -i 's/^:INPUT ACCEPT.*/:INPUT DROP [0:0]/g' /etc/sysconfig/ip6tables
else
>&2 echo 'Remediation is not applicable, nothing was done'
fi