Tag: smtp

Domain-based Message Authentication, Reporting & Conformance (DMARC) Email

DMARC was published in 2012 to build upon the SPF and DKIM email conventions for authorizing senders. It allows specification of policies and provides for reporting of actions performed under those policies.

Assistant:
http://www.kitterman.com/dmarc/assistant.html

DNS Entry Resembles:

_dmarc.example.com TXT v=DMARC1; p=none; rua=mailto:[email protected]; ruf=mailto:[email protected]; fo=0; adkim=r; aspf=r; pct=100; rf=afrf; ri=86400; sp=none

Simple verification…. send an email to this address and you will receive a response with your SPF, DKIM and DMARC compliance status:
mailto:[email protected]

REFERENCES:

DomainKeys Identified Mail (DKIM) Email

DomainKeys (originally from Yahoo!) and Cisco, and later as an industry collaboration, is a means for and organization to claim responsibility for sending a message, in a way that can be validated by a recipient. As a result, emails are “signed” by the outgoing SMTP server and can be verified against a DNS record. Depending upon the receiver, unsigned emails MAY be treated or marked as SPAM as they could be forgeries.

The below instructions assume Ubuntu (Debian) and Postfix, but could likely be modified for other platforms.

  • Install OpenDKIM:
    sudo apt-get install opendkim opendkim-tools
  • Setup initial configuration:

    sudo vi /etc/opendkim.conf

    ADD:
    Domain example.com
    KeyFile /etc/postfix/dkim.key
    Selector dkim
    SOCKET inet:[email protected]
    PidFile /var/run/opendkim/opendkim.pid
    #Canonicalization relaxed/relaxed
    ExternalIgnoreList file:/etc/opendkim/TrustedHostList
    InternalHosts file:/etc/opendkim/TrustedHostList
    LogWhy yes
  • Add trusted hosts… (and folder path, if needed)

    sudo mkdir /etc/opendkim


    sudo vi /etc/opendkim/TrustedHostList
    ADD:

    # External Hosts that OpenDKIM will Trust (add any appropriate values)
    localhost
    127.0.0.1
    10.1.10.1
  • sudo vi /etc/default/opendkim
    ADD:

    SOCKET="inet:[email protected]"
  • sudo vi /etc/postfix/main.cf
    ADD:

    # DKIM
    # --------------------------------------
    milter_default_action = accept
    milter_protocol = 2
    smtpd_milters = inet:127.0.0.1:8891
    non_smtpd_milters = inet:127.0.0.1:8891
  • Take a look around the following file, you may need it later:
    sudo vi /etc/postfix/master.cf
  • Generate your keys:

    opendkim-genkey -t -s dkim -d example.com

    NOTE: this creates dkim.private & dkim.txt, you “might” want to make backups of them 🙂

  • Change permissions on the file:

    sudo chown opendkim:opendkim dkim.private
  • Copy to the postfix folder:

    sudo cp dkim.private /etc/postfix/dkim.key
  • NOTE: I initially had a problem with dkim refusing connections, this MIGHT be needed.

    sudo adduser postfix opendkim
  • Start things back up together:

    sudo service opendkim start
    sudo service postfix restart

  • sudo vi dkim.txt
    (copy contents, remove t=y; as it indicates test mode)
    dkim._domainkey IN TXT ( "v=DKIM1; k=rsa; p=xxxxxxxxx" ) ;

  • Add DNS for DomainKey:

    _domainkey.example.com TXT o=~
  • Add DNS for DKIM:

    dkim._domainkey.example.com TXT v=DKIM1; k=rsa; p=xxxxxxxxx

  • NOTE: you will likely need to wait a few hours for your DNS entries to propagate.

  • Simple verification…. send an email to this address and you will receive a response with your SPF, DKIM and DMARC compliance status:
    mailto:[email protected]

REFERENCES:

Sender Policy Framework (SPF) Email

This is a simple mechanism, using DNS to certify that email from your domain comes from authorized servers. This is accomplished by adding a DNS record to identify the servers from which you send legitimate email. Emails sent from other servers MAY then be assumed as forged (SPAM) and blocked by the receiving email server.

NOTE: This can be easily spoofed, as such it should be a portion of your email security strategy, look into DKIM and DMARC too!

One thing that I initially did not understand… if you are supporting IPv6 and IPv4, you should merge your records onto a single DNS TXT entry:


example.com TXT v=spf1 a mx ip4:xxx.xxx.xxx.xxx ip6:xxxx:x:xxx:xxxx:xxx:xxxx:xxxx:xxx -all

REFERENCES:

Install Splunk Universal Forwarder on Ubuntu

After a while it can get tedious to access and review server logs via the command line. There are several tools available that can provide the same information in a graphical manner. Recently I’ve migrated to Splunk as there are both Enterprise and Free versions available.

  1. Of course, you’ll need a Splunk server installed first, as the forwarder is really just another (lighter) instance that will forward the log information to a central location.
  2. Download the system appropriate installer from:
    http://www.splunk.com/download/universalforwarder
  3. Check to see if you are running 32 or 64 bit OS.uname -aIf you see i686 you are 32 bit, if x86_64 you are 64 bit!
  4. Download, you’ll likely need a different version:sudo dpkg -i splunkforwarder-6.1.3-220630-linux-2.6-intel.deb
    or
    sudo dpkg -i splunkforwarder-6.1.3-220630-linux-2.6-amd64.deb
  5. Enable auto-start on reboot:cd /opt/splunkforwarder/bin/

sudo ./splunk enable boot-start

    1. Start the server:sudo service splunk start
    2. Set the password:

      The default ‘admin‘ password is ‘changeme‘ so we need to change it immediately to do anything else, or we will see errors in future steps.

      sudo /opt/splunkforwarder/bin/splunk edit user admin -password YOUR_NEW_PASSWORD -auth admin:changeme

    3. Set the server:sudo /opt/splunkforwarder/bin/splunk add forward-server YOUR_SERVER_ADDRESS:9997

      NOTE: if you get prompted for a splunk username/password you likely skipped the above step. Remember – the forwarder is a new ‘light’ installation of the server and as such has it’s own users!

    4. Enable some monitors on the box:Some common services and log locations to get you started…
      Apache2 HTTPd
      sudo /opt/splunkforwarder/bin/splunk add monitor /var/log/apache2 -index main -sourcetype Apache2
      Tomcat7
      sudo /opt/splunkforwarder/bin/splunk add monitor /opt/tomcat7/logs -index main -sourcetype Tomcat7
      MySQL
      sudo /opt/splunkforwarder/bin/splunk add monitor /var/log/mysql -index main -sourcetype MySQL
      Postfix (SMTP)
      sudo /opt/splunkforwarder/bin/splunk add monitor /var/log/mail.log -index main -sourcetype Postfix
      Squid3 (Proxy)
      sudo /opt/splunkforwarder/bin/splunk add monitor /var/log/squid/access.log -index main -sourcetype Squid3
      sudo /opt/splunkforwarder/bin/splunk add monitor /var/log/squid/cache.log -index main -sourcetype Squid3

      SonarQube
      sudo /opt/splunkforwarder/bin/splunk add monitor /opt/sonar/logs -index main -sourcetype Sonar
      PM2
      sudo /opt/splunkforwarder/bin/splunk add monitor /home/{user}/.pm2/logs -index main -sourcetype PM2
      NPM
      sudo /opt/splunkforwarder/bin/splunk add monitor /home/scott/.npm/_logs -index main -sourcetype NPM
  1. (OPTIONAL) Verify configuration by opening file at the following:sudo su
    vi /opt/splunkforwarder/etc/apps/search/local/inputs.conf
    exit
  2. You now should be able to log into your server and see new data flowing from the forwarder.

    NOTE: this requires you to enable ‘receiving’ of data on the port specified above, usually 9997.

REFERENCES:

Free Antivirus Software

So, a family member has recently approached me about virus scan products for Windows. It seems that, while he runs a commercial product, it’s a little dated and he does not keep up on the frequent updates, unfortunately this has put him into a position where his computer was infected and has become almost unusable. Using the same commercial products he’s unable to clean up the mess and has already lost many files.

I’ve been a convert to Avast for several years and even run it on my servers to scan for malicious content, it’s both free for non-commercial use and updates automatically.

Other products worth considering:

For Windows:

Unix/Linux:

Mac OS/X:

Cheers!