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Strength

Securing Ubuntu in the cloud

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It is easy to deploy servers to the cloud within a few minutes, you can have a cloud-based server that you (or others can use). ubuntu has a great guide on setting up basic security issues but what do you need to do.

If you do not secure your server expects it to be hacked into. Below are tips on securing your cloud server.

First, read more on scanning your server with Lynis security scan.

Always use up to date software

Always use update software, malicious users can detect what software you use with sites like shodan.io (or use port scan tools) and then look for weaknesses from well-published lists (e.g WordPress, Windows, MySQL, node, LifeRay, Oracle etc). People can even use Google to search for login pages or sites with passwords in HTML (yes that simple).  Once a system is identified by a malicious user they can send automated bots to break into your site (trying millions of passwords a day) or use tools to bypass existing defences (Security researcher Troy Hunt found out it’s child’s play).

Portscan sites like https://mxtoolbox.com/SuperTool.aspx?action=scan are good for knowing what you have exposed.

You can also use local programs like nmap to view open ports

Instal nmap

Find open ports

Limit ssh connections

Read more here.

Use ufw to set limits on login attempts

Only allow known IP’s access to your valuable ports

sudo ufw allow from 123.123.123.123/32 to any port 22

Delete unwanted firewall rules

Only allow known IP’s to certain ports

Also, set outgoing traffic to known active servers and ports

Don’t use weak/common Diffie-Hellman key for SSL certificates, more information here.

More info on generating SSL certs here and setting here and setting up Public Key Pinning here.

Intrusion Prevention Software

Do run fail2ban: Guide here https://www.linode.com/docs/security/using-fail2ban-for-security

I use iThemes Security to secure my WordPress and block repeat failed logins from certain IP addresses.

iThemes Security can even lock down your WordPress.

You can set iThemes to auto lock out users on x failed logins

Remember to use allowed whitelists though (it is so easy to lock yourself out of servers).

Passwords

Do have strong passwords and change the root password provided by the hosts. https://howsecureismypassword.net/ is a good site to see how strong your password is from brute force password attempts. https://www.grc.com/passwords.htm is a good site to obtain a strong password.  Do follow Troy Hunt’s blog and twitter account to keep up to date with security issues.

Configure a Firewall Basics

You should install a firewall on your Ubuntu and configure it and also configure a firewall with your hosts (e.g AWS, Vultr, Digital Ocean).

Configure a Firewall on AWS

My AWS server setup guide here. AWS allow you to configure the firewall here in the Amazon Console.

Type Protocol Port Range Source Comment
HTTP TCP 80 0.0.0.0/0 Opens a web server port for later
All ICMP ALL N/A 0.0.0.0/0 Allows you to ping
All traffic ALL All 0.0.0.0/0 Not advisable long term but OK for testing today.
SSH TCP 22 0.0.0.0/0 Not advisable, try and limit this to known IP’s only.
HTTPS TCP 443 0.0.0.0/0 Opens a secure web server port for later

Configure a Firewall on Digital Ocean

Configuring a firewall on Digital Ocean (create a $5/m server here).  You can configure your Digital Ocean droplet firewall by clicking Droplet, Networking then Manage Firewall after logging into Digital Ocean.

Configure a Firewall on Vultr

Configuring a firewall on Vultr (create a $2.5/m server here).

Don’t forget to set IP rules for IPV4 and IPV6, Only set the post you need to allow and ensure applications have strong passwords.

Ubuntu has a firewall built in (documentation).

Enable the firewall

Adding common ports

sudo ufw allow ssh/tcp
sudo ufw logging on
sudo ufw allow 22
sudo ufw allow 80
sudo ufw allow 53
sudo ufw allow 443
sudo ufw allow 873
sudo ufw enable
sudo ufw status
sudo ufw allow http
sudo ufw allow https

Add a whitelist for your IP (use http://icanhazip.com/ to get your IP) to ensure you won’t get kicked out of your server.

sudo ufw allow from 123.123.123.123/24 to any port 22

More help here.  Here is a  good guide on ufw commands. Info on port numbers here.

If you don’t have a  Digital Ocean server for $5 a month click here and if a $2.5 a month Vultr server here.

Backups

rsync is a good way to copy files to another server or use Bacula

Basics

Initial server setup guide (Digital Ocean).

Sudo (admin user)

Read this guide on the Linux sudo command (the equivalent if run as administrator on Windows).

Users

List users on an Ubuntu OS (or compgen -u)

Common output

Add User

e.g

Add user to a group

Show users in a group

This will show users in a group

Remove a user

Rename user

Change user password

Groups

Show all groups

compgen -ug

Common output

compgen -g
root
daemon
bin
sys
adm
tty
disk
lp
mail
proxy
sudo
www-data
backup
irc
etc

You can create your own groups but first, you must be aware of group ids

cat /etc/group

Then you can see your systems groups and ids.

Create a group

Permissions

Read this https://help.ubuntu.com/community/FilePermissions

How to list users on Ubuntu.

Read more on setting permissions here.

Chmod help can be found here.

Install Fail2Ban

I used this guide on installing Fail2Ban.

Check Fail2Ban often and add blocks to the firewall of known bad IPs

Best practices

Ubuntu has a guide on basic security setup here.

Startup Processes

It is a good idea to review startup processes from time to time.

Accounts

  • Read up on the concept of least privilege access for apps and services here.
  • Read up on chmod permissions.

Updates

Do update your operating system often.

Minimal software

Only install what software you need

Exploits and Keeping up to date

Do keep up to date with exploits and vulnerabilities

Secure your applications

  • NodeJS: Enable logging in applications you install or develop.

Ban repeat Login attempts with FailBan

Fail2Ban config

Hosts File Hardening

Add

Add a whitelist with your ip on /etc/fail2ban/jail.conf (see this)

Restart the service

sudo service fail2ban restart
sudo service fail2ban status

Intrusion detection (logging) systems

Tripwire will not block or prevent intrusions but it will log and give you a heads up with risks and things of concern

Install Tripwire.

Running Tripwire

This will scan your system for issues of note

My Output.

sudo nano /var/log/tiger/security.report.username.170809-18:42

Security scripts *** 3.2.3, 2008.09.10.09.30 ***
Wed Aug  9 18:42:24 AEST 2017
20:42> Beginning security report for username (x86_64 Linux 4.4.0-89-generic).

# Performing check of passwd files...
# Checking entries from /etc/passwd.
--WARN-- [pass014w] Login (bob) is disabled, but has a valid shell.
--WARN-- [pass014w] Login (root) is disabled, but has a valid shell.
--WARN-- [pass015w] Login ID sync does not have a valid shell (/bin/sync).
--WARN-- [pass012w] Home directory /nonexistent exists multiple times (3) in
         /etc/passwd.
--WARN-- [pass012w] Home directory /run/systemd exists multiple times (2) in
         /etc/passwd.
--WARN-- [pass006w] Integrity of password files questionable (/usr/sbin/pwck
         -r).

# Performing check of group files...

# Performing check of user accounts...
# Checking accounts from /etc/passwd.
--WARN-- [acc021w] Login ID dnsmasq appears to be a dormant account.
--WARN-- [acc022w] Login ID nobody home directory (/nonexistent) is not
         accessible.

# Performing check of /etc/hosts.equiv and .rhosts files...

# Checking accounts from /etc/passwd...

# Performing check of .netrc files...

# Checking accounts from /etc/passwd...

# Performing common access checks for root (in /etc/default/login, /securetty, and /etc/ttytab...
--WARN-- [root001w] Remote root login allowed in /etc/ssh/sshd_config

# Performing check of PATH components...
--WARN-- [path009w] /etc/profile does not export an initial setting for PATH.
# Only checking user 'root'

# Performing check of anonymous FTP...

# Performing checks of mail aliases...
# Checking aliases from /etc/aliases.

# Performing check of `cron' entries...
--WARN-- [cron005w] Use of cron is not restricted

# Performing check of 'services' ...
# Checking services from /etc/services.
--WARN-- [inet003w] The port for service ssmtp is also assigned to service
         urd.
--WARN-- [inet003w] The port for service pipe-server is also assigned to
         service search.

# Performing NFS exports check...

# Performing check of system file permissions...
--ALERT-- [perm023a] /bin/su is setuid to `root'.
--ALERT-- [perm023a] /usr/bin/at is setuid to `daemon'.
--ALERT-- [perm024a] /usr/bin/at is setgid to `daemon'.
--WARN-- [perm001w] The owner of /usr/bin/at should be root (owned by daemon).
--WARN-- [perm002w] The group owner of /usr/bin/at should be root.
--ALERT-- [perm023a] /usr/bin/passwd is setuid to `root'.
--ALERT-- [perm024a] /usr/bin/wall is setgid to `tty'.

# Checking for known intrusion signs...
# Testing for promiscuous interfaces with /bin/ip
# Testing for backdoors in inetd.conf

# Performing check of files in system mail spool...

# Performing check for rookits...
# Running chkrootkit (/usr/sbin/chkrootkit) to perform further checks...
--WARN-- [rootkit004w] Chkrootkit has detected a possible rootkit installation
Possible Linux/Ebury - Operation Windigo installetd

# Performing system specific checks...
# Performing checks for Linux/4...

# Checking boot loader file permissions...
--WARN-- [boot02] The configuration file /boot/grub/menu.lst has group
         permissions. Should be 0600
--FAIL-- [boot02] The configuration file /boot/grub/menu.lst has world
         permissions. Should be 0600
--WARN-- [boot06] The Grub bootloader does not have a password configured.

# Checking for vulnerabilities in inittab configuration...

# Checking for correct umask settings for init scripts...
--WARN-- [misc021w] There are no umask entries in /etc/init.d/rcS

# Checking Logins not used on the system ...

# Checking network configuration
--FAIL-- [lin013f] The system is not protected against Syn flooding attacks
--WARN-- [lin017w] The system is not configured to log suspicious (martian)
         packets

# Verifying system specific password checks...

# Checking OS release...
--WARN-- [osv004w] Unreleased Debian GNU/Linux version `stretch/sid'

# Checking installed packages vs Debian Security Advisories...

# Checking md5sums of installed files

# Checking installed files against packages...
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.dep' does not
         belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.alias.bin' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.devname' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.softdep' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.alias' does not
         belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.symbols.bin'
         does not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.builtin.bin'
         does not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.symbols' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-87-generic/modules.dep.bin' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.dep' does not
         belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.alias.bin' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.devname' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.softdep' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.alias' does not
         belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.symbols.bin'
         does not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.builtin.bin'
         does not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.symbols' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/modules/4.4.0-89-generic/modules.dep.bin' does
         not belong to any package.
--WARN-- [lin001w] File `/lib/udev/hwdb.bin' does not belong to any package.

# Performing check of root directory...

# Checking device permissions...
--WARN-- [dev003w] The directory /dev/block resides in a device directory.
--WARN-- [dev003w] The directory /dev/char resides in a device directory.
--WARN-- [dev003w] The directory /dev/cpu resides in a device directory.
--FAIL-- [dev002f] /dev/fuse has world permissions
--WARN-- [dev003w] The directory /dev/hugepages resides in a device directory.
--FAIL-- [dev002f] /dev/kmsg has world permissions
--WARN-- [dev003w] The directory /dev/lightnvm resides in a device directory.
--WARN-- [dev003w] The directory /dev/mqueue resides in a device directory.
--FAIL-- [dev002f] /dev/rfkill has world permissions
--WARN-- [dev003w] The directory /dev/vfio resides in a device directory.

# Checking for existence of log files...
--FAIL-- [logf005f] Log file /var/log/btmp permission should be 660
--FAIL-- [logf007f] Log file /var/log/messages does not exist

# Checking for correct umask settings for user login shells...
--WARN-- [misc021w] There is no umask definition for the dash shell
--WARN-- [misc021w] There is no umask definition for the bash shell

# Checking symbolic links...

# Performing check of embedded pathnames...
20:47> Security report completed for username.

More on Tripwire here.

Hardening PHP

Hardening PHP config (and backing the PHP config it up), first create an info.php file in your website root folder with this info

Now look for what PHP file is loadingPHP Config

Back that your PHP config file

TIP: Delete the file with phpinfo() in it as it is a security risk to leave it there.

TIP: Read the OWASP cheat sheet on using PHP securely here and securing php.ini here.

Some common security changes

Don’t forget to review logs, more config changes here.

Antivirus

Yes, it is a good idea to run antivirus in Ubuntu, here is a good list of antivirus software

I am installing ClamAV as it can be installed on the command line and is open source.

ClamAV help here.

Scan a folder

Setup auto-update antivirus definitions

I set auto updates 24 times a day (every hour) via daemon updates.

tip: Download manual antivirus update definitions. If you only have a 512MB server your update may fail and you may want to stop fresh claim/php/nginx and mysql before you update to ensure the antivirus definitions update. You can move this to a con job and set this to update at set times over daemon to ensure updates happen.

Manual scan with a bash script

Create a bash script

Bash script contents to update antivirus definitions.

Edit the crontab to run the script every hour

Uninstalling Clam AV

You may need to uninstall Clamav if you don’t have a lot of memory or find updates are too big.

Setup Unattended Ubuntu Security updates

At login, you should receive

Other

  • Read this awesome guide.
  • install Fail2Ban
  • Do check your log files if you suspect suspicious activity.

Check out the extensive Hardening a Linux Server guide at thecloud.org.uk: https://thecloud.org.uk/wiki/index.php?title=Hardening_a_Linux_Server

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