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Securing Google G Suite email by setting up SPF, DKIM and DMARC with Cloudflare

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This post will show you how you can setup Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM) Signatures and Domain-based Message Authentication, Reporting, and Conformance (DMARC) on your GMail (G Suite) email to limit spam and increase security.

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I have a number of guides on moving away form CPanel, Setting up VM’s on AWS, Vultr or Digital Ocean along with installing and managing WordPress from the command line. I use Google G Suite to send and receive emails that are linked to my domain (even via the command line) using multiple domains (with aliases).

Buy how can you extend your email security and limit spam?

Enter..

Sender Policy Framework (SPF) for Authorizing Use of Domains in Email

Background: SPF summary from the RFC document from the Internet Engineering Task Force (IETF).

“Email on the Internet can be forged in a number of ways. In particular, existing protocols place no restriction on what a sending host can use as the “MAIL FROM” of a message or the domain given on the SMTP HELO/EHLO commands. This document describes version 1 of the Sender Policy Framework (SPF) protocol, whereby ADministrative Management Domains (ADMDs) can explicitly authorize the hosts that are allowed to use their domain names, and a receiving host can check such authorization.”

Google has a guide in setting up SPF records for your G Suite account.

Scan your site for SPF, DKIM and DMARC configuration(s).

Gmail has a test site where you can check your site SPF, DKIM and DMARC etc: https://toolbox.googleapps.com/apps/checkmx/

Secure GSuite

How to set up an SPF Record

I followed this guide to set up an SPF record on my G Suite account. I use Cloudflare for my DNS provider so I’ll make my DNS changes there.

Add SPF Record

Update: Google instructions were wrong, use a TXT record and not a SPF record.

Read more on SPF at Wikipedia here.

DNS will take a while to replicate so do wait a few hours before checking again with the checkmx tool.

Now let’s set up DomainKeys Identified Mail (DKIM) Signatures

Read more on DKIM at Wikipedia here.

Background: The DKIM RFC form the Internet Engineering Task Force (IETF) states…

“DomainKeys Identified Mail (DKIM) permits a person, role, or organization that owns the signing domain to claim some responsibility for a message by associating the domain with the message. This can be an author’s organization, an operational relay, or one of their agents. DKIM separates the question of the identity of the Signer of the message from the purported author of the message. Assertion of responsibility is validated through a cryptographic signature and by querying the Signer’s domain directly to retrieve the appropriate public key. Message transit from author to recipient is through relays that typically make no substantive change to the message content and thus preserve the DKIM signature.”

Google has a DKIM FAQ: https://support.google.com/a/answer/174124

Login to your G Suite account and load this FAQ.

The FAQ page states..

“You can help prevent spoofing by adding a digital signature to outgoing message headers using the DKIM standard. This involves using a private domain key to encrypt your domain’s outgoing mail headers, and adding a public version of the key to the domain’s DNS records. Recipient servers can then retrieve the public key to decrypt incoming headers and verify that the message really comes from your domain and hasn’t been changed along the way.”

Click Generate the Domain Key

Generate Domain Key

Follow the steps and generate a key

Generate Key

Generate a new record

Generate key

Add the DKIM key to your DNS record

Add DNS record

DNS will take a while to replicate so do wait a few hours before checking again with the checkmx tool.

Domain-based Message Authentication, Reporting, and Conformance (DMARC)

Read more on DMARC at Wikipedia here. Read the official page here https://dmarc.org/.

Background: The DMARC RFC form the Internet Engineering Task Force (IETF) states…

DMARC Flow

DMARC Flow

“Domain-based Message Authentication, Reporting, and Conformance (DMARC) is a scalable mechanism by which a mail-originating organization can express domain-level policies and preferences for message validation, disposition, and reporting, that a mail-receiving organization can use to improve mail handling.

Originators of Internet Mail need to be able to associate reliable and authenticated domain identifiers with messages, communicate policies about messages that use those identifiers, and report about mail using those identifiers. These abilities have several benefits: Receivers can provide feedback to Domain Owners about the use of their domains; this feedback can provide valuable insight about the management of internal operations and the presence of external domain name abuse.

DMARC does not produce or encourage elevated delivery privilege of authenticated email. DMARC is a mechanism for policy distribution that enables increasingly strict handling of messages that fail authentication checks, ranging from no action, through altered delivery, up to message rejection.”

Google G Suite has a guide to setting up a DMARC record here

Snip from the Google guide here..

“Spammers can sometimes forge the “From” address on email messages so the spam appears to come from a user in your domain. To help prevent this sort of abuse, Google is participating in DMARC.org, which gives domain owners more control over what Gmail does with spam email messages from their domain.

G Suite follows the DMARC.org standard and allows you to decide how Gmail treats unauthenticated emails coming from your domain. Domain owners can publish a policy telling Gmail and other participating email providers how to handle unauthenticated messages sent from their domain. By defining a policy, you can help combat phishing to protect users and your reputation.“

Login to your G Suite account and load this FAQ

Click Add A DMARC Record

Add DMARC

You will then need to set up a DKIM Domain Key (if you have not done so yet)

When you are done you need to choose your DMARC rules, I would suggest you go to https://mxtoolbox.com/DMARCRecordGenerator.aspx to generate a record

I generated these rules

Dmarc Rules

Warning: Setting a DMARC policy that is too strict may block mail from being delivered. Tighten rules over time.

Login to your DNS provider and add your TXT record.

DMARC Record

You should now have an SPF, DKIM and DMARC record in DNS.

DNS

Update: The SPD record above should be a TXT (Google led me astray)

DNS will take a while to replicate so do wait a few hours before checking again with the checkmx tool.

Now go to bed and wait for DNS to replicate.

Troubleshooting SPF

My TXT record would not validate with https://toolbox.googleapps.com/apps/checkmx/check

Google Toolbox

The MX Toolbox SPF checker reports that SPF records are deprecated and to use TXT records instead.

SPF TXT Record

Fix (remove the SPF record and add a TXT record with the same contents). Don’t forget to delete the old SPF record.

TXT Record

Results

SPF Setup

Reports

SPF/DKIM reports will let me know when unauthorized people send email from my domain.

Also, DMARC will alert me to unauthorized activity

 

I hope this guide helps someone.

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Revision History

v1.4 Reports

v1.3 DMARC Flow image

V1.2 Updated wording

V1.1 Fixed typos (they were free)

v1.0 Initial post

How to be alerted after system boot on Ubuntu 16.04 with an email via Gmail

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This will allow you to sent an email at startup on Ubuntu boot. You will need to ensure sendmail is setup and working (read my guide on How to send email via G Suite from Ubuntu in the cloud, setup an Ubuntu server in the cloud here (guide here)).

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Create a  scripts folder

Create a file called /scripts/emailstartup.sh and add..

optional: Uncomment lines above to attach a zip file instead of a log file (don’t forget to attach the zip instead of the log file in sendmail.)

Make the script file executable

Test the script

Add the following to crontab -e to ensure the script is executed 5 minutes after startup.

 

On reboot, you will be emailed desired start-up information.

email capture

 

 

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v1.0 initial post

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.

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If you do not secure your server expect 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

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.

TypeProtocolPort RangeSourceComment
HTTPTCP800.0.0.0/0Opens a web server port for later
All ICMPALLN/A0.0.0.0/0Allows you to ping
All trafficALLAll0.0.0.0/0Not advisable long term but OK for testing today.
SSHTCP220.0.0.0/0Not advisable, try and limit this to known IP’s only.
HTTPSTCP4430.0.0.0/0Opens 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

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.

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

Common output

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

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

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.

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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v1.92 added hardening a linux server link