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Outlook Security: Why You Should Deploy MFA for Office 365


Multi-factor authentication, or MFA (sometimes known as two-factor authentication, or 2FA), is recommended whenever basic usernames and passwords aren’t enough for protecting sensitive logins.

If you’ve ever been asked to confirm your identity by entering a code sent to your phone, you’ve used MFA. The method is widely used for online banking accounts, to bolster security when employees remotely access corporate sites, and to help satisfy HIPAA requirements. More and more, though, we’re advising its use to protect all access to Office 365.

We’re making this recommendation because of the experiences of some of our newer clients. It’s a sad fact that organizations often discover they need our security services only after they’ve been victimized. Several have turned to us after making tens of thousands of dollars in payments that were never received, because the money was sent to fraudulent bank accounts. That’s when they called us in to untangle what happened.

Who’s Reading My Emails?

We’ve found a new breed of criminals who specialize in hijacking email accounts. They’re very sophisticated, expert in covering their tracks, and victims are none the wiser — until it’s too late and the money’s gone.

It all starts with compromised login credentials that criminals use to gain access to one or more individuals’ email accounts. The perpetrator either tricks the individual into giving up the credentials with a phishing email, or simply purchases lists of stolen login credentials on the dark web. Once access is obtained, the criminal lurks and learns, watches and waits. The goal is to find out who moves the money and how. Who are the approvers? Who gives the instructions? Who executes the transactions?

Or Worse, Who’s Sending My Emails?

Less sophisticated criminals would be content to send a bogus invoice. This new sort is looking for legitimate transactions conducted in the normal course of business. They intercept those transactions by issuing instructions to send the money to different accounts, masquerading as the authorized worker. They’re sending these emails from the actual mailboxes, complete with signatures, so the communications look legitimate. Of course, because these are sent using the real email accounts, the compromised users would see the bogus messages in their outbox, or the inbox would contain replies to messages they never sent. To avoid detection, the criminal sets rules in the Outlook account to immediately delete the bogus messages based on the subject line.

Here’s an example of a sophisticated criminal attack; this happened to an engineering firm with about 20 employees. The criminal had the email credentials for the employee responsible for payroll, and also knew, from reading the emails, who the firm’s third-party payroll provider was. Trying the employee’s email credentials on the payroll account revealed that the employee used the same password in both places. Now it was simple to log in to the payroll provider and re-route all the direct deposits to accounts the criminal controlled.  An entire month’s payroll was lost before the theft was discovered.

Detection and Prevention

There are two approaches to dealing with these kinds of attacks. One is detection, through SOC monitoring. SOC monitoring issues alerts for suspicious email access, such as a user accessing from a different location or device, or a user simultaneously logged in from two locations or devices. Either of these is an indicator of unauthorized access of an email account.

Prevention is where MFA comes in. In addition to username and password (something the user knows), MFA adds an additional factor (something the user possesses). The additional factor is the user’s smartphone. Unless the criminal also steals the employee’s phone, the compromised login credentials are useless. There are several approaches to implementing MFA:

  1. Some third-party applications that do single sign-on have MFA capabilities. Examples include Okta and Duo. Microsoft Azure also supports MFA.
  2. Office 365 has the ability to natively enable MFA through the Microsoft Authenticator application. However, some companies have issues with mandating that employees install specific applications on their personal smartphones. If the company doesn’t reimburse employees for their phone use, this becomes a concern for the HR department.
  3. Office 365 also supports native MFA by sending a one-time passcode to the employee’s phone via a text message. This gets around the reimbursement issue because it doesn’t require loading a specific application on the phone. Plus, the simplicity of the approach allows employees to self-enroll through an eight-step process that requires less than two minutes to complete. The impact on the employee is minimal, because the one-time passcode is required only when the employee is logging in from an unknown location or device.

At FIT Solutions, our managed IT services include implementing the multiple forms of MFA. We also perform SOC monitoring through our cybersecurity offering, SOCBOX. You can learn more about FIT Solutions managed IT services, or better yet, call us at (888) 339-5694.

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