CRIN Trac: Ticket #2: Set up firewall and fail2ban to stop brute force ssh attacks

hours changed; totalhours set

chris — Tue, 28 Apr 2015 13:41:10 GMT

hours changed from 0 to 0.25
totalhours set to 0.25

Install:

aptitude install iptables-persistent fail2ban

Create /etc/fail2ban/jail.local containing:

# See http://www.pontikis.net/blog/fail2ban-install-config-debian-wheezy
[DEFAULT]
ignoreip  = 127.0.0.1 93.95.228.179
bantime   = 86400
#destemail = chris@webarchitects.co.uk
banaction = iptables-multiport
#action    = %(action_mwl)s
# JAILS
[ssh]
enabled   = true
maxretry  = 3

Restart:

service fail2ban restart

Edit /etc/iptables/rules.v4 which originally contained:

# Generated by iptables-save v1.4.21 on Tue Apr 28 13:27:23 2015
*filter
:INPUT ACCEPT [2:104]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [2:336]
:fail2ban-ssh - [0:0]
-A INPUT -p tcp -m multiport --dports 22 -j fail2ban-ssh
-A fail2ban-ssh -j RETURN
COMMIT
# Completed on Tue Apr 28 13:27:23 2015

To config from existing servers:

# Generated by iptables-save v1.4.21 on Tue Apr 28 13:27:23 2015
*filter
:INPUT ACCEPT [2:104]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [2:336]
:fail2ban-ssh - [0:0]
-A INPUT -p tcp -m multiport --dports 22 -j fail2ban-ssh
-A fail2ban-ssh -j RETURN
# Allows all loopback (lo0) traffic and drop all traffic to 127/8 that doesn't use lo0
-A INPUT -i lo -j ACCEPT
-A INPUT ! -i lo -d 127.0.0.0/8 -j REJECT
# Accepts all established inbound connections
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# Allows all outbound traffic
# You could modify this to only allow certain traffic
-A OUTPUT -j ACCEPT
# Allows HTTP and HTTPS connections from anywhere (the normal ports for websites)
-A INPUT -p tcp --dport 80 -j ACCEPT
-A INPUT -p tcp --dport 443 -j ACCEPT
# Allows SSH connections
# THE -dport NUMBER IS THE SAME ONE YOU SET UP IN THE SSHD_CONFIG FILE
#-A INPUT -p tcp -m state --state NEW --dport 22 -j ACCEPT
# Allow ping
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
# mysql allow 93.95.228.180
#-A INPUT -p tcp -d 93.95.228.180 --dport 3306 -j ACCEPT
-A INPUT -p tcp -s 93.95.228.180 --dport 3306 -j ACCEPT
-A INPUT -p tcp --dport 3306 -j DROP
# log iptables denied calls (access via 'dmesg' command)
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
# Reject all other inbound - default deny unless explicitly allowed policy:
-A INPUT -j REJECT
-A FORWARD -j REJECT
COMMIT
# Completed on Tue Apr 28 13:27:23 2015

Reload and check:

iptables-restore < /etc/iptables/rules.v4
iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
fail2ban-ssh  tcp  --  anywhere             anywhere             multiport dports ssh
ACCEPT     all  --  anywhere             anywhere
REJECT     all  --  anywhere             loopback/8           reject-with icmp-port-unreachable
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:https
ACCEPT     icmp --  anywhere             anywhere             icmp echo-request
ACCEPT     tcp  --  crin2.crin.org       anywhere             tcp dpt:mysql
DROP       tcp  --  anywhere             anywhere             tcp dpt:mysql
LOG        all  --  anywhere             anywhere             limit: avg 5/min burst 5 LOG level debug prefix "iptables denied: "
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
Chain fail2ban-ssh (1 references)
target     prot opt source               destination
RETURN     all  --  anywhere             anywhere

Disable IPv6 as we are not setting it up right now, add the following to /etc/sysctl.conf:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

The above now needs doing for crin2.

hours, totalhours changed

chris — Tue, 28 Apr 2015 13:48:53 GMT

hours changed from 0 to 0.05
totalhours changed from 0.25 to 0.3

aptitude install iptables-persistent fail2ban
vi /etc/fail2ban/jail.local
service fail2ban restart
vi /etc/iptables/rules.v4
iptables-restore < /etc/iptables/rules.v4
vi /etc/sysctl.conf

The following was added to rules.v4:

# https://wiki.debian.org/iptables
# Allows all loopback (lo0) traffic and drop all traffic to 127/8 that doesn't use lo0
-A INPUT -i lo -j ACCEPT
-A INPUT ! -i lo -d 127.0.0.0/8 -j REJECT
# Accepts all established inbound connections
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# Allows all outbound traffic
# You could modify this to only allow certain traffic
-A OUTPUT -j ACCEPT
# Allows HTTP and HTTPS connections from anywhere (the normal ports for websites)
-A INPUT -p tcp --dport 80 -j ACCEPT
-A INPUT -p tcp --dport 443 -j ACCEPT
# Allows SSH connections
# THE -dport NUMBER IS THE SAME ONE YOU SET UP IN THE SSHD_CONFIG FILE
-A INPUT -p tcp -m state --state NEW --dport 22 -j ACCEPT
# Allow ping
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
# log iptables denied calls (access via 'dmesg' command)
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
# Reject all other inbound - default deny unless explicitly allowed policy:
-A INPUT -j REJECT
-A FORWARD -j REJECT

Check the rules:

iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
fail2ban-ssh  tcp  --  anywhere             anywhere             multiport dports ssh
ACCEPT     all  --  anywhere             anywhere
REJECT     all  --  anywhere             loopback/8           reject-with icmp-port-unreachable
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:https
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh
ACCEPT     icmp --  anywhere             anywhere             icmp echo-request
LOG        all  --  anywhere             anywhere             limit: avg 5/min burst 5 LOG level debug prefix "iptables denied: "
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
Chain fail2ban-ssh (1 references)
target     prot opt source               destination
RETURN     all  --  anywhere             anywhere

That should do for now for this issue.

hours, status, totalhours changed; resolution set

chris — Tue, 28 Apr 2015 13:58:50 GMT

hours changed from 0 to 0.1
status changed from new to closed
resolution set to fixed
totalhours changed from 0.3 to 0.4

Just tested the ssh servers and I had to uncomment this for crin1:

-A INPUT -p tcp -m state --state NEW --dport 22 -j ACCEPT

Think this ticket can now be closed as resolved.

cc changed

chris — Thu, 18 Jun 2015 11:57:05 GMT

cc jenny gillian added; jonas removed

CCs changed.