RedHat

Posted on August 23, 2022 by admin

The following is a very basic guide for setting up Fail2ban for SSH.

Install and basic config

Install Fail2ban

sudo dnf install fail2ban

You may need to install the epel repo

sudo yum install epel-release

Configure to run on system boot

sudo systemctl enable fail2ban

Start Fail2ban service

sudo systemctl start fail2ban

Copy config file with

sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local

Modify the config file

nano /etc/fail2ban/jail.local

Uncomment the following line and add any IPs that need to be whitelisted

ignoreip = 127.0.0.1/8 ::1 192.168.1.20

Save the file and restart Fail2Ban

sudo systemctl restart fail2ban

Configuring Fail2Ban for SSH

Create a new jail file in /etc/fail2ban/jail.d/ called sshd.local

nano /etc/fail2ban/fail.d/sshd.local

Add the following. Note: if you are using a custom ssh port, change “port = ssh” to “port = portnumber”

[sshd]
enabled = true
port = ssh
action = iptables-multiport
logpath = /var/log/secure
maxretry = 5
bantime = 300

Restart Fail2ban

sudo systemctl restart Fail2ban

You can list the firewall rules to verify that an IP gets banned.

iptables -S | grep ipaddress

Unbanning an IP Address

You can unban an IP address with the following command.

sudo fail2ban-client set sshd unbanip 192.168.1.100

You can check out the following link for more information

https://www.redhat.com/sysadmin/protect-systems-fail2ban

WHM/cPanel Firewall

Posted on June 23, 2020 by admin

Had a weird issue where a certain address was unable to access the cpanel server, but it was intermittent with it working some times, but failing at other times.

Ended up being the firewall on the WHM server blocking that particular IP address due to failed log in attempts.

Check the status of LFD (Login Failure Daemon)

systemctl status lfd

How do I know which IP’s are being blocked?

Check the logs, dmesg or tail /var/log/messages

[1122639.674605] Firewall: UDP_IN Blocked IN=eth0 OUT= MAC=8e:23:f5:16:a6:b1:cc:51:54:6a:2e:ea:14:00 SRC=72.211.105.113 DST=192.168.1.12 LEN=64 TOS=0x00 PREC=0x00 TTL=246 ID=40014 PROTO=UDP SPT=9307 DPT=161 LEN=44
[1122646.728510] Firewall: TCP_IN Blocked IN=eth0 OUT= MAC=8e:23:f5:16:a6:b1:cc:51:54:6a:2e:ea:14:00 SRC=198.199.98.83 DST=192.168.1.12 LEN=40 TOS=0x00 PREC=0x00 TTL=244 ID=54321 PROTO=TCP SPT=57522 DPT=15672 WINDOW=65535 RES=0x00 SYN URGP=0

CSF keeps a file with addresses to deny in “/etc/csf/csf.deny” Also nice that if gives you a little bit of info on why it was blocked.

# grep -r "192.168.1.21" /etc/csf/csf.deny
192.168.1.21 # lfd: (pop3d) Failed POP3 login from 192.168.1.21 (US/United States/-): 10 in the last 3600 secs - Tue Jun 20 11:36:15 2020

You can also dump all of the rule in iptables with

iptables --list | egrep "192.168.1.21"

Change 192.168.1.21 with the IP you are looking for

Whitelist IP Addresses

Open up /etc/csf/csf.allow with a text editor and add the IP to the bottom of the file.

or add the IP address to the end of the file with the following command. Replace 192.168.1.21 with the IP address you want to whitelist.

echo "192.168.1.21" >> /etc/csf/csf.allow

You can also do all of this from the WHM web interface “Plugins -> ConfigServer Security & Firewall”

semanage Allow and Delete ports in CentOS

Posted on April 27, 2018 by admin

The commands are for CentOS, but should work on Fedora and RedHat.

If semanage is not installed refer to here.

You would typically use this along with the systems firewall to allow a port through. Guide for firewalld and iptables. If you change it in the firewall and fail to add/edit it in semanage you can potentially get weird behavior like sshd not wanting to start after changing the port.

Add port

semanage port -a -t ssh_port_t -p tcp 2222

The above command allows the sshd service to start, using port 2222.

List allowed ports

semanage port -l

You can use grep to filter the results

Example:

[admin@localhost ~]# semanage port -l | grep ssh
ssh_port_t tcp 2222, 22
[admin@localhost ~]#

Delete port

semanage port -d -p tcp 2222

Other examples

Allow SNMP

semanage port -a -t snmp_port_t -p udp 161

Allow WHM/cPanel ssh logins from specific IP addresses using iptables

Posted on January 20, 2018 by admin

For some reason the hosts.allow and hosts.deny files don’t seem to work on cPanel. One of the alternative methods to limit ssh logins to specific addresses is to use iptables.

Allow access from specific IP addresses.

Replace 192.168.1.0/24 and 192.168.0.0/24 with your addresses. You can add more addresses using the “,”. Also if your ssh port is not the default port, be sure to change it.

iptables -A INPUT -s 192.168.1.0/24,192.168.0.0/24 -p tcp --dport 22 -j ACCEPT

Reject access from everywhere else

iptables -A INPUT -s 0.0.0.0/0 -p tcp --dport 22 -j REJECT

You can see your rules with

 iptables -L --line-numbers

If you need to add another rule after the fact, you’ll need to make sure that it is above the REJECT rule. you can use the “-I” to insert it between rules.

Example: inserts rule as the second rule in the INPUT chain

iptables -I INPUT 2 -s 192.168.42.0/24 -p tcp --dport 22 -j ACCEPT

Add, List, and Delete iptable rules

Posted on January 20, 2018 by admin

Add iptable rule

The following rule rejects access to port 22 on all devices except ones on the 192.168.1.0/24 network. Note the “!”. This command can be useful for a WHM/cPanel server to limit ssh access.

iptables -A INPUT ! -s 192.168.1.0/24 -p tcp --dport 22 -j REJECT

List iptable rules with line numbers

iptables -L --line-numbers

Example output

root@localhost [~]# iptables -L --line-numbers
Chain INPUT (policy ACCEPT)Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
1 REJECT tcp -- !192.168.1.11 anywhere tcp dpt:ssh reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT)
num target prot opt source destination

Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
1 ACCEPT tcp -- anywhere anywhere multiport dports smtp,urd,submission owner GID match mailman
2 cpanel-dovecot-solr all -- anywhere anywhere

Chain cpanel-dovecot-solr (1 references)
num target prot opt source destination
1 ACCEPT tcp -- anywhere anywhere multiport sports 8984,7984 owner UID match cpanelsolr

Remove iptable rule

To delete a rule use the -D option with the Chain and the line number. So to delete the first rule in the example output above, we would specify the INPUT chain and the the line number 1

 iptables -D INPUT 1

How to Open a Port on Redhat, CentOS or Fedora Linux

Posted on November 24, 2012 by admin

By default iptables firewall stores its configuration at /etc/sysconfig/iptables file. You need to edit this file and add rules to open port number.

Note: if you have SELinux enabled, you’ll need to allow the port with semanage.

Open port 80

To open a different port just enter the port number.

Open flle /etc/sysconfig/iptables:

# vi /etc/sysconfig/iptables

Append rule as follows:

A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT

Save and close the file. Restart iptables:

# /etc/init.d/iptables restart

or,

#service iptables restart

Verify that port is open

Run the following command:

netstat -tulpn | less

Make sure iptables is allowing the port you enabled:

iptables -L -n

If you need more info you can refer to the man page:

man iptables

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Tag Archives: iptables