Microsoft DOESN’T admit expiring-password rules are useless

Update 6th June 2019: The final version of the Security Baseline has been released by Microsoft, and explains the password recommendations very clearly. Here’s one paragraph quoted, bold is my emphasis, but please go and read the whole article:

Periodic password expiration is an ancient and obsolete mitigation of very low value, and we don’t believe it’s worthwhile for our baseline to enforce any specific value. By removing it from our baseline rather than recommending a particular value or no expiration, organizations can choose whatever best suits their perceived needs without contradicting our guidance. At the same time, we must reiterate that we strongly recommend additional protections even though they cannot be expressed in our baselines.

Original blogpost:

CNET has an article titled “Microsoft admits expiring-password rules are useless” which I strongly disagree with, and thought it was worth explaining why.

Beyond the actual blog post from Aaron Margosis at Microsoft not actually containing the word ‘useless’, it’s an inaccurate summary of what is a well written and clear write-up from where I sit.

This all came out of publishing the draft of the Security Baseline recommendations for Windows 10 1903, which details out what settings Microsoft recommend and why. If you’re managing a Windows environment, these are a must read, and should be reviewed with each version of Windows 10 you plan to move to.

The general take of the CNET article was that password changes have been useless for years, suggests Microsoft should completely ‘yank’ the ability to force passwords to expire, and if your IT staff don’t remove password expiry immediately, they’re living in a ‘security Stone Age’. It’s rather insulting and coming from someone in my opinion, who doesn’t know what they’re talking about. They might say the same about me, of course :)

On the other hand, Microsoft’s blog post tells a different story. Yes, passwords are problematic and forcing them to change frequently causes other issues where people just change the number on the end by ‘1’, but they aren’t saying password changes are useless.

Microsoft used to recommend 90 day expiries, then to 60 days. The idea there was that if a credential is leaked somehow, the smaller window that the password is known by third parties, the better. But, if your password M0nkey34! is now M0nkey35!, that’s probably going to be the first thing a targeted attacker tries if the password they had for you didn’t work.

Although all this is true, it works on the assumption that someone is actively targeting you. It happens, but it’s much more common for attackers to just do spray attacks based on millions of credentials they have. Why are they going to pick your account and try a bunch of combinations of passwords, when they could just go through stupid amounts of records with no effort and find weaknesses there?

Say you are a target for some reason; it’s likely that the password leaked from somewhere isn’t new – it’s probably months or years old. If you’d never changed your password because your company never forced it to change, then the attacker now has a valid password for you.

It’s also much more likely your password was stolen from a 3rd party service, nothing to do with your corporate systems. You might have signed up with your work email address, but the password ‘should’ be unique to the service signed up for. We all know users don’t work that way, and use the same password all over the place. Having a password they know will change frequently, may mean that they use something at least unique, even if it does increment.

All of this is moot of course, if you have multi-factor authentication (MFA) in place, because the requirement of something else (a phone, bio-metrics etc) means a username and password by themselves are actually useless. However, most companies do have systems in place that have no options around MFA, so what do they do?

To re-iterate, I agree with everything said in Microsoft’s blog post. This is where one paragraph in the blog post sums it up nicely:

Periodic password expiration is an ancient and obsolete mitigation of very low value, and we don’t believe it’s worthwhile for our baseline to enforce any specific value. By removing it from our baseline rather than recommending a particular value or no expiration, organizations can choose whatever best suits their perceived needs without contradicting our guidance. At the same time, we must reiterate that we strongly recommend additional protections even though they cannot be expressed in our baselines.

Work out your risks, your userbase, what systems might be impacted, what extra protection you have in place and make an informed decision around what frequency works for you.

The focus shouldn’t be on password changes, but should be on implementing those other protections in all scenarios – but before that happens (which for many companies can easily take several years), you’ll need to work out what policy you do. There is no single best-fit recommendation on what that is when using pure passwords, because they’re inherently bad however you look at them.

Look at Conditional Access, Password Protection and Azure AD Identity Protection for starters on adding in these extra protections!

The answer isn’t a pure ‘password changes are useless’, and it’s irresponsible to say so.

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