self-service password reset

Impact of Removing SMS As an MFA Method In Azure AD

There are a number of general recommendations that SMS (text messages) as an MFA method is not a good idea (mainly to do with the ease of porting or moving devices the number is associated with). You should always be looking at MFA with an app (Microsoft Authenticator or other) or hardware device. But the default in Azure AD is to include SMS as an option – so if we turn off text messaging as a second factor what is the impact to our user base who might have already registered their phone number.

My previous article on MFA end user experiences covered the different options available for the different registration wizards (legacy and the new combined MFA/SSPR wizard), what happens if you have SSPR enabled (and what happens if you do not). Each of the scenarios in that article allowed the user to register a phone number and then to have a text message sent at login.

If the user registered with the legacy authentication wizard (which is the default setting as of the time of writing) then there are three options by default – authentication phone, office number (set by the admin and not by the user) and mobile app (and phone is the selected option). Using SMS for second factor is therefore automatically set up unless the user chooses “office number” or “mobile app” whilst registering. The registration page looks as follows:

So in scenarios where the user followed the defaults they get an MFA prompt at login that looks like this:

Notice that they have an option to “sign in another way” for scenarios where the user maybe cannot receive a phone call but would be able to receive a text message (if you are in a location where you can receive neither, then you need to register the app as well in advance). If the user clicks “sign in another way” then they see the following where they can choose to receive a text message as the second factor proof:

Second factor proof select phone or text

To disable SMS/text as an MFA method you need to be in the Azure AD portal > MFA > Additional cloud-based MFA settings (or click Multi-Factor Authentication in the Users page of the same portal). You will see the below once you click the Service Settings tab:

This dialog includes the “skip multi-factor authentication…” box which you only have if you have Azure AD P1 or P2 licence. The four options at the bottom include the “Text message to phone” – uncheck that to stop SMS as a second factor.

So if SMS/text is removed as an option – what changes for the users who has already got a phone number stored as a MFA method? First change is that “sign in another way” message is now missing. A user who previously got a phone call with the option to change to another option will find that they cannot change options anymore (unless they have also registered a different method such as office number or mobile app:

Therefore if there is not enough mobile signal to manage a call (and there might be for a text message) then the user cannot authenticate.

What about users who when they registered for MFA set SMS as their default? Setting text message as a default is not a obvious setting – but the default is whatever you initially choose to register with – so in the registration wizard if you select “send me a code by text message” then your default is SMS:

Once the admin disables SMS as a valid second factor, those users with phone as their default (or app) are not impacted – but users who set text message as their default are required to re-register. In the registration they are told their organization needs further information, that “call me” is the only available option, but their previously registered telephone number is shown in the registration wizard. This is shown in the following series of images:

Registration for MFA - Call only as a phone option

Once the users settings are saved, the user clicks Finish and their registration for phone authentication is updated to remove text message as a valid option. Enabling texts again in the admin portal does not allow this user to use texts again unless they register again or they update their additional security verification settings (Office 365 browser app > click photo > My account > Manage security & privacy > Additional security verification > Update your phone numbers used for account security (go to https://aka.ms/mfasetup as a shortcut to avoid all these steps)

If you remove both phone and text as a registration option as shown then users who previously only had phone and/or text registered will be required to register again.

Disable all phone and text options for MFA

This time registration will default to “mobile app” – where the user can select “code” or “notification” as their new default:

MFA Registration - phone and text disabled

In scenarios where you have enabled the new registration wizard (see my previous article on MFA end user experiences for more on this) then the default registration option is to use the app and not phone or text, though phone numbers are collected if you also turn on two or more options for requiring a password reset with SSPR. So in these scenarios you will probably find that the user has lots of registered options and so turning off SMS is not an issue.

So to disable SMS is only a problem in Azure AD for the user – as it means that at the next login they need to register again (so not a real problem). I had previously seen in 2018 that if the admin disabled text messages then users could not login if this was their only method! So that issue is clearly fixed now.

So as a call to action from this article – consider turning off text messages as a second factor and noting that the only impact is some users will either need to register again or you can ask them to go to https://aka.ms/mfasetup beforehand to change their default setting.

A long request within Azure AD/Office 365 has been the request to be able to register your security info from a known location or only on certain other conditions. Well it looks like this has appeared in Azure AD in the last few days!!

Its visible under Azure AD > Conditional Access > New/Existing Policy > Cloud Apps or Actions:

So, what does this look like in practice? Lets put this preview to the test.

Create the Conditional Access Policy for User Actions

Open the Azure AD portal at https://aad.portal.azure.com and click Enterprise Applications

From here click Conditional Access (this is also accessible under Azure AD > Security as well)

Click Add Policy and give the policy a name. I have chosen “Register Security Information On-Premises” for here

Click Users and Groups. I have selected “Users and Groups” rather than “All Users” as I plan to test this out first! I have picked the group that I use for testing Conditional Access changes. Eventually I will change this to All Users so that no-one can register security info apart from when on a trusted location. Note that this would also I think include guest users – I need to test that! Guest users are by their very nature not on my network but I might have MFA required for them – so they need to register, but I don’t want to apply the below to them

Select Cloud Apps or Actions (this was recently renamed to support this functionality we are describing here)

Select User Actions in the slider and check the option for Register Security Information (Preview)

Select Conditions and select the conditions you want to apply when users are registering security information. Its probably location based, so I will set that up here.

Select Locations, click Yes under Configure and select Any Location under Include and then under Exclude select Trusted Locations. Note that you need to have set up trusted locations in Conditional Access as well – I’m going to assume the public IP of all your offices is added and marked as trusted.

This setting will ensure that all locations other than trusted locations cannot register security information – note that this is the reverse of what you might expect. We need to block the locations we don’t want to access the MFA/SSPR registration process rather than the reverse. This is because we are required to add a control to the rules

With Azure AD P2 licences you could user a sign-in risk condition, ensuring that registration does not happen on medium or high risk sign-ins!

Click Done to bring you back to the first blade of settings and set Enable Policy to On to turn on this feature

Under Access Controls, click Grant and choose Block Access – be very careful here – don’t block all your access to everything!

Click Done

This takes us back to the first blade in the Conditional Access settings.

Click On in the Enable Policy slider

Now the Create button is available – this is not available if you do not create the reverse of what you might expect to do – block unknown locations rather than allow trusted locations!

Click Create

You will get your notification – you can test this in a few minutes:

Enable The New Combined MFA/SSPR Registration Page

Though I noticed that this conditional access restriction works against the older MFA registration page, Microsoft have said in their release blog article for this feature that it will only work against the new MFA/SSPR combined registration page. Therefore you should turn this on for your users impacted by the above policy – initially for your pilot users and then for all users.

See https://techcommunity.microsoft.com/t5/Azure-Active-Directory-Identity/Cool-enhancements-to-the-Azure-AD-combined-MFA-and-password/ba-p/354271 for more on setting up the combined MFA/SSPR registration page.

Testing Register Security Information (Preview)

In an in-private browser session on the Wi-Fi of your favourite coffee company, browse to https://aka.ms/mfasetup (as this is not a trusted location!)

After logging in you would expect to be take to the registration page for MFA and SSPR – but you are not!

Repeat your test from on-premises, and you will get the MFA and SSPR registration pages (or both if you have the new combined MFA+SSPR wizard enabled):

Note that for a brand new user where you have SSPR enabled, they are required to register by default every 180 days. This will mean they have to register at first login – therefore first login needs to be from a trusted network (in this example) – you could use Trusted Device as the only place to register from, but adding a user to a trusted device requires MFA by default, so watch out for an issue here and if you want to do this, test it very well.

I have not had the opportunity to test this with the 180 day refresh of your settings – presumably that should work from any location and only changing them would be blocked, but this is something that needs to be tried out.