Microsoft MFA calls to landline no longer being received

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gbwelly

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#242501 31-Oct-2018 14:38

Up until recently we have been happily using Azure AD MFA, with a mixture of users using the app, and some electing to receive a voice call. At some stage recently, calls to NZ land lines stopped working. People using mobile phones are still receiving the verification call, but those using Vodafone and Spark land lines do not get called. Our telco does not see any incoming calls from the source phone number, and is pushing back saying the problem is at Microsoft's end, which my feeling is that it's probably the case.

What do you guys reckon has happened?

freitasm

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#2117447 31-Oct-2018 14:58

Assuming no undisclosed specifics (you didn't mention recent change of service providers, number porting, etc), then I think you should contact Microsoft support for this case.

gbwelly

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#2117454 31-Oct-2018 15:12

freitasm:

Assuming no undisclosed specifics (you didn't mention recent change of service providers, number porting, etc), then I think you should contact Microsoft support for this case.

Sorry, forgot the obvious, yes a support call with Microsoft has been raised.

Nothing has been changed at our end. MS Support are denying it's a problem and we are not getting any escalation. I would like to present them with a likely explanation of what might have changed at their end.

freitasm

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#2117455 31-Oct-2018 15:15

Your telco providers did confirm no incoming calls?

Have you tried turning MFA off for a test account then on again?

gbwelly

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#2117843 1-Nov-2018 13:48

To bring closure to this, the source phone number for the MFA call was being blocked by both Vodafone and Spark, but only for landlines. Our provider stated to us that there were no calls logged from that number in the days it wasn't working. They didn't say that it was blocked however. I interpret this to mean that either they share a block list, or there is a mechanism upstream from both providers for blocking. Either way, changing the source phone number got it working. It is concerning that this can happen though.

vonfluffy

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#2123733 11-Nov-2018 21:36

How did you change the source of the call?

We are experiencing similar... but with kordia as the upstream provider..
We are only just testing landlines as an authentication mechanism as have always used mobile or app till now.

gbwelly

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#2123800 12-Nov-2018 07:40

vonfluffy:

How did you change the source of the call?

Go to the azure portal at https://portal.azure.com

Go to Azure Active Directory -> MFA -> Phone call settings. There is a box where you can change the US phone number.

We weren't sure of the number format rules for the US, so just incremented the last digit.

freitasm

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#2123801 12-Nov-2018 07:43

Another reason for people to use TOTP instead of SMS or phone calls... If you add one cog to the machine (the telco) things are more likely to fail.

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

gbwelly

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#2123804 12-Nov-2018 08:02

freitasm:

Another reason for people to use TOTP instead of SMS or phone calls... If you add one cog to the machine (the telco) things are more likely to fail.

Then every system you want to add MFA to needs to support a box to type the TOTP code into. So you wouldn't use approve/deny in the app either? That requires Wifi or data via a telco.

freitasm

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#2123852 12-Nov-2018 08:22

TOTP is time-based, does not rely on a telco in the middle.

My point is that a system with less components is usually more fail-proof than a system with more.

gbwelly

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#2123890 12-Nov-2018 08:37

freitasm: My point is that a system with less components is usually more fail-proof than a system with more.

I don't disagree. Nor do I want to anger the BDFL by arguing too much. :-)

I'm simply saying there are situations where TOTP doesn't work. App or voice call approve/deny can be applied to anything that talks RADIUS.

Personally I think voice call is crusty-as, but I have a few crusty-as users who don't have cell phones. Yes you read that.

freitasm

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#2123893 12-Nov-2018 08:42

I don't doubt it.