Why you should block legacy authentication

Currently, we could say that Legacy Authentication is one of the most compromising sign-in, luckily for us, older protocols have been replacing with modern authentication services, taking the advantage that MA supports MFA, while Legacy Authentication refers to all protocols that use Basic Authentication, and only requires one method of authentication.

So, it is important thar for security reasons we need to disable legacy authentication in our environments, why? Because enabling MFA isn’t effective if legacy protocols are not blocked. For example, the following options are considered legacy authentication protocols:

  • Authenticated SMTP – Used by POP and IMAP clients to send email messages.
  • Autodiscover – Used by Outlook and EAS clients to find and connect to mailboxes in Exchange Online.
  • Exchange ActiveSync (EAS) – Used to connect to mailboxes in Exchange Online.
  • Exchange Online PowerShell – Used to connect to Exchange Online with remote PowerShell. If you block Basic authentication for Exchange Online PowerShell, you need to use the Exchange Online PowerShell Module to connect.
  • Exchange Web Services (EWS) – A programming interface that’s used by Outlook, Outlook for Mac, and third-party apps.
  • IMAP4 – Used by IMAP email clients.
  • MAPI over HTTP (MAPI/HTTP) – Used by Outlook 2010 and later.
  • Offline Address Book (OAB) – A copy of address list collections that are downloaded and used by Outlook.
  • Outlook Anywhere (RPC over HTTP) – Used by Outlook 2016 and earlier.
  • Outlook Service – Used by the Mail and Calendar app for Windows 10.
  • POP3 – Used by POP email clients.
  • Reporting Web Services – Used to retrieve report data in Exchange Online.
  • Other clients – Other protocols identified as utilizing legacy authentication

How can we monitor the usage of legacy authentication in Azure AD?

Thanks to Log Analytics, Insights and workbooks, we are able to monitor the use of those protocols, for instance:

And check the non-interactive sign-ins (be careful with ADConnect sync accounts):

What we can do to avoid this?

The best way to block or report legacy authentication for users is use Conditional Access policies (Does my organization need Azure AD Conditional Access? – Albandrod’s Memory (albandrodsmemory.com) & Enabling zero trust security in your environment – Albandrod’s Memory (albandrodsmemory.com)

But the best way is creating a CA policy:

My final advice

Legacy authentication must be disabled to protect our environments, but first, start small and analyse the impact in your organization.

Till next time!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s