How to secure an Ubuntu 12.04 LTS server – Part 2 The GUI installer script

22/03/2019 Categories: Réseau, Sécurité, Système Tags: , , Comments off

Source: The Fan Club

This guide is based on various community forum posts and webpages. Special thanks to all. All comments and improvements are very welcome as this is purely a personal experimental project at this point and must be considered a work in progress.

The Ubuntu Server Secure script:

  • The Ubuntu Server Secure script is set of GUI security administration tools to harden and audit the security on an Ubuntu 12.04 LTS server by using a GUI shell script to install and configure various security features found in How to secure an Ubuntu 12.04 LTS server – Part 1 The Basics.
  • This script was done as an experiment in using Zenity to create a interactive Gnome Gtk+ GUI installer.
  • Zenity is a great tool for creating a simple yet powerful GUI user interface on top of bash like shell script very quickly.

Requirements:

  • Ubuntu 12.04 LTS server with a standard LAMP stack installed.
  • Unity or Gnome Desktop installed.
  • Zenity installed. (Zenity installed by default in Ubuntu 12.04 LTS Desktop)

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How to secure an Ubuntu 12.04 LTS server – Part 1 The Basics

21/03/2019 Categories: Réseau, Sécurité, Système Tags: , , Comments off

Source: The Fan Club

This guide is based on various community forum posts and webpages. Special thanks to all. All comments and improvements are very welcome as this is purely a personal experimental project at this point and must be considered a work in progress.

This guide is intended as a relatively easy step by step guide to:

Harden the security on an Ubuntu 12.04 LTS server by installing and configuring the following:

  1. Install and configure Firewall – ufw
  2. Secure shared memory – fstab
  3. SSH – Key based login, disable root login and change port
  4. Apache SSL – Disable SSL v3 support
  5. Protect su by limiting access only to admin group
  6. Harden network with sysctl settings
  7. Disable Open DNS Recursion and Remove Version Info  – Bind9 DNS
  8. Prevent IP Spoofing
  9. Harden PHP for security
  10. Restrict Apache Information Leakage
  11. Install and configure Apache application firewall – ModSecurity
  12. Protect from DDOS (Denial of Service) attacks with ModEvasive
  13. Scan logs and ban suspicious hosts – DenyHosts and Fail2Ban
  14. Intrusion Detection – PSAD
  15. Check for RootKits – RKHunter and CHKRootKit
  16. Scan open Ports – Nmap
  17. Analyse system LOG files – LogWatch
  18. SELinux – Apparmor
  19. Audit your system security – Tiger

Requirements:

  • Ubuntu 12.04 LTS or later server with a standard LAMP stack installed.

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Debian / Ubuntu / CentOs – Block DDOS attacks with No More DDOS (formerly : DDoS Deflate)

21/03/2019 Categories: Réseau, Sécurité Tags: , , , Comments off

If you arrive on this page, is that you have already received a DDoS attack on your server or you want to protect it before this attack happens on your server.
In this tutorial, we will install « No More DDoS » (replacing DDoS Deflate that is no longer maintained by its author) that lets you easily protect you against small DDoS attacks.

This script is available in 2 versions :

  1. the Debian version, compatible with : Debian 6/7/8, Ubuntu Server 13.10, Ubuntu Server 14.04, Linux Mint 17 and distributions based on Debian.
  2. the CentOs version, compatible with : CentOs 6/7, RHEL 6/7 (à venir dans la version 2.0), Fedora 20 (coming in version 2.0), and distributions based on CentOs.
  1. Install No More DDoS
  2. Configure No More DDoS
  3. No More DDoS GUI
  4. Update No More DDoS
  5. Uninstall No More DDoS

1. Install No More DDoS

To install « No More DDoS for Debian« , use the following command :

wget -O- https://raw.githubusercontent.com/stylersnico/nmd/master/debian/install.sh | sh

To install »No More DDoS for CentOS 7 » use the following command :

wget -O- https://raw.githubusercontent.com/stylersnico/nmd/master/centos/install.sh | sh

2. Configurer No More DDoS

To configure No More DDoS, edit the « /usr/local/nmd/conf.d/agent.conf » file :

vim  /usr/local/nmd/conf.d/agent.conf

In this file, you can edit the following information :

  • FREQ : Interval time between 2 launches of the script. By default, this script is run once per minute.
  • NO_OF_CONNECTIONS : Corresponds to the maximum number of established connections to an IP address. If an IP address has more than 500 connections established on your server, this IP will be banned.
  • APF_BAN : By default, the script blocks IP addresses in the firewall with iptables (APF_BAN=0). To use « APF », specify 1 (APF_BAN=1).
  • EMAIL_TO : If you wish to be notified when blocking a DDoS attack, enter your email address at this line. If you leave this empty, then, no e-mail will be sent.
  • BAN_PERIOD : Period during an IP address is blocked. Default : 3600 seconds = 1 hour.

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Categories: Réseau, Sécurité Tags: , , ,

Protect DDOS attacks

20/03/2019 Categories: Réseau, Sécurité Tags: , , , , , Comments off

Protect DDOS attacks

Using ModEvasive agains DDoS attacksprotect ddos attacks

The first think to do is to install ModEvasive. All details are provided in http://hardenubuntu.com/hardening/apache/modsecurity/.

Configuring UFW

The following instructions can be added to the UFW rules. Edit the /etc/ufw/before.rules:

sudo vi /etc/ufw/before.rules

Add those lines after *filter near the beginning of the file:

:ufw-http - [0:0]
:ufw-http-logdrop - [0:0]

Add those lines near the end of the file, before the COMMIT:

### Start HTTP ###

# Enter rule
-A ufw-before-input -p tcp --dport 80 -j ufw-http
-A ufw-before-input -p tcp --dport 443 -j ufw-http

# Limit connections per Class C
-A ufw-http -p tcp --syn -m connlimit --connlimit-above 50 --connlimit-mask 24 -j ufw-http-logdrop

# Limit connections per IP
-A ufw-http -m state --state NEW -m recent --name conn_per_ip --set
-A ufw-http -m state --state NEW -m recent --name conn_per_ip --update --seconds 10 --hitcount 20 -j ufw-http-logdrop

# Limit packets per IP
-A ufw-http -m recent --name pack_per_ip --set
-A ufw-http -m recent --name pack_per_ip --update --seconds 1 --hitcount 20 -j ufw-http-logdrop

# Finally accept
-A ufw-http -j ACCEPT

# Log
-A ufw-http-logdrop -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW HTTP DROP] "
-A ufw-http-logdrop -j DROP

### End HTTP ###

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Resolving “nf_conntrack: table full, dropping packet.” flood message in dmesg Linux kernel log

20/03/2019 Categories: Réseau, Sécurité Tags: , , , Comments off

Source: pc-freak.net

nf_conntrack_table_full_dropping_packet
On many busy servers, you might encounter in /var/log/syslog or dmesg kernel log messages like

nf_conntrack: table full, dropping packet

to appear repeatingly:

[1737157.057528] nf_conntrack: table full, dropping packet.
[1737157.160357] nf_conntrack: table full, dropping packet.
[1737157.260534] nf_conntrack: table full, dropping packet.
[1737157.361837] nf_conntrack: table full, dropping packet.
[1737157.462305] nf_conntrack: table full, dropping packet.
[1737157.564270] nf_conntrack: table full, dropping packet.
[1737157.666836] nf_conntrack: table full, dropping packet.
[1737157.767348] nf_conntrack: table full, dropping packet.
[1737157.868338] nf_conntrack: table full, dropping packet.
[1737157.969828] nf_conntrack: table full, dropping packet.
[1737157.969928] nf_conntrack: table full, dropping packet
[1737157.989828] nf_conntrack: table full, dropping packet
[1737162.214084] __ratelimit: 83 callbacks suppressed

There are two type of servers, I’ve encountered this message on:

1. Xen OpenVZ / VPS (Virtual Private Servers)
2. ISPs – Internet Providers with heavy traffic NAT network routers

I. What is the meaning of nf_conntrack: table full dropping packet error message

In short, this message is received because the nf_conntrack kernel maximum number assigned value gets reached.
The common reason for that is a heavy traffic passing by the server or very often a DoS or DDoS (Distributed Denial of Service) attack. Sometimes encountering the err is a result of a bad server planning (incorrect data about expected traffic load by a company/companeis) or simply a sys admin error…

– Checking the current maximum nf_conntrack value assigned on host:

linux:~# cat /proc/sys/net/ipv4/netfilter/ip_conntrack_max
65536

– Alternative way to check the current kernel values for nf_conntrack is through:

linux:~# /sbin/sysctl -a|grep -i nf_conntrack_max
error: permission denied on key 'net.ipv4.route.flush'
net.netfilter.nf_conntrack_max = 65536
error: permission denied on key 'net.ipv6.route.flush'
net.nf_conntrack_max = 65536

– Check the current sysctl nf_conntrack active connections

To check present connection tracking opened on a system:

:

linux:~# /sbin/sysctl net.netfilter.nf_conntrack_count
net.netfilter.nf_conntrack_count = 12742

The shown connections are assigned dynamicly on each new succesful TCP / IP NAT-ted connection. Btw, on a systems that work normally without the dmesg log being flooded with the message, the output of lsmod is:

linux:~# /sbin/lsmod | egrep 'ip_tables|conntrack'
ip_tables 9899 1 iptable_filter
x_tables 14175 1 ip_tables

On servers which are encountering nf_conntrack: table full, dropping packet error, you can see, when issuing lsmod, extra modules related to nf_conntrack are shown as loaded:

linux:~# /sbin/lsmod | egrep 'ip_tables|conntrack'
nf_conntrack_ipv4 10346 3 iptable_nat,nf_nat
nf_conntrack 60975 4 ipt_MASQUERADE,iptable_nat,nf_nat,nf_conntrack_ipv4
nf_defrag_ipv4 1073 1 nf_conntrack_ipv4
ip_tables 9899 2 iptable_nat,iptable_filter
x_tables 14175 3 ipt_MASQUERADE,iptable_nat,ip_tables

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