Databases, Systems & Networks

Appropriate firewall rules heavily depend on the services being run. Below are iptables rulesets to secure your Linode if you’re running a web server. These are given as an example! A real production web server may want or require more or less configuration and these rules would not be appropriate for a file or database server, Minecraft or VPN server, etc.

iptables rules can always be modified or reset later, but these basic rulesets serve only as a beginning demonstration.

IPv4

/tmp/v4

*filter

# Allow all loopback (lo0) traffic and reject traffic
# to localhost that does not originate from lo0.
-A INPUT -i lo -j ACCEPT
-A INPUT ! -i lo -s 127.0.0.0/8 -j REJECT

# Allow ping and traceroute.
-A INPUT -p icmp --icmp-type 3 -j ACCEPT
-A INPUT -p icmp --icmp-type 8 -j ACCEPT
-A INPUT -p icmp --icmp-type 11 -j ACCEPT

# Allow SSH connections.
-A INPUT -p tcp -m state --state NEW --dport 22 -j ACCEPT

# Allow HTTP and HTTPS connections from anywhere
# (the normal ports for web servers).
-A INPUT -p tcp --dport 80 -j ACCEPT
-A INPUT -p tcp --dport 443 -j ACCEPT

# Accept inbound traffic from established connections.
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

# Log what was incoming but denied (optional but useful).
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables_INPUT_denied: " --log-level 7

# Reject all other inbound.
-A INPUT -j REJECT

# Log any traffic which was sent to you
# for forwarding (optional but useful).
-A FORWARD -m limit --limit 5/min -j LOG --log-prefix "iptables_FORWARD_denied: " --log-level 7

# Reject all traffic forwarding.
-A FORWARD -j REJECT

COMMIT


Optional: If you plan to use Linode Longview, add this additional rule below the section for allowing HTTP and HTTPS connections:

# Allow incoming Longview connections 
-A INPUT -s longview.linode.com -m state --state NEW -j ACCEPT

 

Lire la suite…

Few days ago, my friend’s WordPress website went down. After investigation, I have figured out that it was receiving massive amount of posts requests to the xmlrpc.php file, which brings the apache and mysql to eat up all the system resources and the website crashed. Fortunately, I have figured out the way to mitigate this attack using Fail2Ban, which I’ll share in this post.

Install the Fail2Ban package using the following command:

apt-get install fail2ban iptables

Make a local copy of jail.conf file for configuration change:

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

Lire la suite…

You would like to block outgoing access to particular remote host/ip or port for all or selected service/port. In this quick tutorial I will explain how to use iptables to block outgoing access.

Block Access To Outgoing IP Address

The following rule will block ip address 202.54.1.22 from making any outgoing connection:

iptables -A OUTPUT -d 202.54.1.22 -j DROP

The above will block chat server ip address or site having dangerous contains such as viruses or malware.

Block Access To Outgoing IP TCP / UDP Port Number

To block specific port number such tcp port # 5050, enter:
iptables -A OUTPUT -p tcp --dport 5050 -j DROP

To block tcp port # 5050 for an IP address 192.168.1.2 only, enter:
iptables -A OUTPUT -p tcp -d 192.168.1.2 --dport 5050 -j DROP

Finally, you need to save your firewall rules. Under CentOS / RHEL / Fedora Linux, enter:
# /sbin/service iptables save
OR
# /etc/init.d/iptables save

Source: Mellowhost