How to enable serial console KVM guest os.

 1. Enable serial console with command :

 systemctl enable --now serial-getty@ttyS0.service  

2. Connecting to guest OS from KVM with command:

 virsh console [VM_NAME]  

ref: ostechnix.com

How to fix expired Freeradius certificate problem.

Problem :

    1. Can't start RADIUS Systemd service.

    2. Log show like this. 

 Oct 9 00:00:49 radius1 sh[1114]: C = FR, ST = Radius, L = Somewhere, O = Example Inc., emailAddress = admin@example.org, CN = Example Certificate Authority  
 Oct 9 00:00:49 radius1 sh[1114]: error 10 at 1 depth lookup: certificate has expired  
 Oct 9 00:00:49 radius1 sh[1114]: C = FR, ST = Radius, O = Example Inc., CN = Example Server Certificate, emailAddress = admin@example.org  
 Oct 9 00:00:49 radius1 sh[1114]: error 10 at 0 depth lookup: certificate has expired  
 Oct 9 00:00:49 radius1 sh[1114]: error server.pem: verification failed  
 Oct 9 00:00:49 radius1 sh[1114]: make: *** [Makefile:107: server.vrfy] Error 2  
 Oct 9 00:00:49 radius1 rsyslogd[1098]: imjournal: journal files changed, reloading... [v8.1911.0-6.el8 try https://www.rsyslog.com/e/0 ]  
 Oct 9 00:00:49 radius1 systemd[1]: radiusd.service: Control process exited, code=exited status=2  
 Oct 9 00:00:49 radius1 systemd[1]: radiusd.service: Failed with result 'exit-code'.  
 Oct 9 00:00:49 radius1 systemd[1]: Failed to start FreeRADIUS high performance RADIUS server..  

Cause :

    Certificate file in `/etc/raddb/certs/` have any expired certificates.

Resolution 1 (If you do not user certificate in /Certs ) :

    Delete all certificate files in `/raddb/certs` with this command.

 rm -f *.pem *.der *.csr *.crt *.key *.p12 serial* index.txt*  

Resolution 2 :

     Create new certificate new certificate instead expired certs. 

   

Basic Firewalld configuration for Linux server

1. Show all zone name and information about those zone.

 firewall-cmd --list-all-zones  

2. Create new zone.

 firewall-cmd --new-zone=dmz2 --permanent

3. Add source network or source IP to firewall zone to allow those network access allow services or port number in specific zone.

 firewall-cmd --zone=dmz2 --add-source=192.168.0.0/24 --permanent  
 firewall-cmd --reload  #Apply

4. Add service port to allow sources network in a zone to access those port.

 firewall-cmd --zone=dmz2 --add-port=80/tcp --add-port=443 --permanent  
 firewall-cmd --reload  #apply

Simple way to install go for CENTOS

1. Download Go From Go Site 
2. Untar Go to /usr/local/
   

   tar -C /usr/local -xzf go-xx.tar

3. Create Link in /usr/bin
   

   ln -s /usr/bin/go/ /usr/local/go/bin

4. Create Go Working Directory

5. mkdir /go
   

6. Set GOPATH 

   export GOPATH=/go

How to add network interface card (NIC) to Docker’s container and bridging with phisical NIC

1. Create Docker Network
• # docker network create --driver=bridge [docker's network name]
• *Docker automatically create network bridge with brctl when running command (for linux environment).
2. Bridge created network with another interface
• # brctl addif [brid name] [NIC’s name]
• *brctl show (for lookup bridge name).
• **Manual add interface to bridge everytime after restart host.
3. Create Docker Cointainer
4. Connect Docker to bridge
• # docker network connect [Network Name] [Container ID]
• *Container will be connect and automatically create another interface on container that connect with created network.

Detection and Prevention SSH Brute Force Attacks with Logstash and iptables

This topic talking about alternative way to "Detect and Prevent ssh brute force" 

for Linux Server with logstash ipset and iptables on CentOS7

First Step: Create Preventive Mechanism 

Create a preventive mechanism with iptable and ipset for blocking an attack source 

with brute force's source ip.

install and config ipset: 

 yum -y install ipset  
 ipset create block hash:ip  

config iptables rule:

iptables -A INPUT -p tcp -m set --match-set block src -j DROP  

Second Step: Create Detection Mechanism

Install and config Logstash for analyze sshd log (/var/log/secure) to identify 

source ip address of ssh brute force

enable logstash on boot:

systemctl enable logstash  

config logstash: copy this configuration and replace in to file "/etc/logstash/conf.d/logstash"

 input{  
      file{  
           path => ["/var/log/secure"]  
      }  
 }  
 output{  
      #push output to file  
      file {path => "/var/log/blacklist"}  
 #     stdout { codec => json_lines }  
 }  
 filter{  
      grok {  
           match => ["message","%{MONTH:month}(?: | )%{MONTHDAY:day} %{TIME:time} %{WORD} %
{WORD:prog}\[%{DATA}: %{DATA:detail}(?: logname=(?:%{WORD:logname}|)|)(?: uid=(?:%{WORD:uid}|)|)(?: euid=(?:%{WORD:euid}|)|)(?: tty=(?:%{WORD:tty}|)|)(?: ruser=(?:%{WORD:ruser}|)|) rhost=%{IP:remoteIP}(?: user=%{DATA:remoteUser}|)"]  
           remove_field => ["message"]  
      }  
      #drop event if remoteIP is missing.  
      if ![remoteIP] {  
           drop { }  
      }  
      # block remoteIP when authentication fail 3 time.  
      throttle {  
           before_count => 0  
           after_count => 3  
           period => 30  
           key => "%{remoteIP}"  
           add_field => { "block" => "true"}  
      }  
      if [remoteIP] and [block] == "true"{  
           ruby {  
                code => "  
                      `/usr/sbin/ipset add block #{event['remoteIP']} timeout 86400 `  
                "  
           }  
      }  
 }  

restart logstash service: 

systemctl restart logstash

optional : You can send event data form logstash to elasticsearch for long-term analyze 

Install Network Manager Plugin for OpenVPN on Ubuntu

1. Install Network Manager Ubuntu
# apt-get install network-manager-openvpn

2. Config OpenVPN Connection

2.1 Open "Network Connection" then Click "Add" button

2.2 Choose a Connection Type "OpenVPN"

2.3 Edit VPN Connection

Gateway: VPN Server Name
Authentication Type: Password with Certificates (TLS)
Username: VPN Username
Password: VPN Password
User Certificate:  xxx.crt
CA Certificate: ca.crt
Private Key: xxx.key
then click "Advanced Option"

2.4 Edit Advanced Option

Select Option
- Use LZO data compression
- Use a TAP device