Re: Account Lockout Policies

{...reposting...I think I might have triggered a word filter on the

Microsoft servers, never saw it arrive there...}

Account lockout is a poor substitute for good passwords -- and is one of the

most expensive security features you can use. Let's think about this by

considering the threat. What threat does account lockout (attempt to)

mitigate? Password guessing. How can you make password guessing attacks

become useless for an attacker? Two ways: implement lockouts or use good

(meaning long) passwords.

Consider the first choice, account lockouts. The typical cost to an

organization to reset locked accounts is US$75 per help desk call. In a

medium or large organization, this can become a very high monthly

maintenance cost. In nearly all instances, the call results from users

locking themselves out, not users encountering locked out accounts because

some bad guy was trying to guess passwords. Account lockouts have one

more -- very bad -- problem: they *create* opportunities for bad guys to

conduct denial-of-service attacks against accounts or entire domains! Even

if you use a timed unlock of, say, 15 minutes, then the attacker can write

his script to churn through thousands of bogus logon attempts every 15

minutes 2 seconds. So, contrary to your claim, enabling this setting

actually can have significant impact on usability.

Account lockout is there for people who absolutely need it. But I can't

think of any instance where this is true. Instead, have a policy that

requires simple passwords at least 15 characters long. Forget about

complexity rules that force people to write down passwords. A simple

15-character passphrase (think short sentence) is easy to remember, quick to

type, and far stronger than any short complex password. A passphrase like

this will withstand any kind of automated password attack, including those

based on rainbow tables. And you can even use a method that helps you

remember unique phrases for each site, if you wish:

* web mail: "my dog and i got the mail"

* shopping: "my dog and i bought some stuff"

* office: "my dog and i went to work"

* photo site: "my dog and i admired some art"

This is why we disable account lockout by default. There are much better --

and much less expensive -- ways to mitigate the threat.

You're right, there's no built-in method to automatically disable unused

accounts. A variety of third-party products can provide you with this

functionality. I suspect some of them might be free, perhaps simple scripts

even. I tried searching on "automatically disable unused accounts" and saw a

few hits that looked promising. This particular function, however, rightly

belongs in the HR process. A number of customers I've spoken with have

automated the account creation/disablement/deletion process, incorporating

it into HR systems. When a new user is hired, the account is created when

the user departs, the account is disabled some time later, it's deleted.

The HR systems take care of this, not domain or enterprise administrators. I

wrote more about this subject here:

http://blogs.technet.com/steriley/archive/2007/05/31/when-you-say-goodbye-to-an-employee.aspx

Password expiration is an important setting for everyone. It mitigates two

threats: employees sharing passwords and bad guys discovering passwords.

Because we can eliminate the second threat using long simple passphrases as

I described above, then we have only one remaining threat: password sharing.

Your estimation of how prevalent this threat is in your environment will

guide you toward choosing an expiration time that works for you. 42 days is

a reasonable default our own corpnet uses 70 days. My experience with most

customers shows that password sharing isn't a problem. So for those who do

enforce long simple passphrases, I suggest that a reasonable default for

expiration is 120 days.

Windows begins notifying you 14 days before your password expires. You can

change this time period through group policy. I was in a similar situation

recently. Last month my domain password expired while I was in Australia for

TechEd there. I could continue to log on to my laptop with cached

credentials (so I'm not sure why you say your laptops become bricked?), but

couldn't use Outlook Web Access or RPC+HTTP of course. So I connected to a

Terminal Server computer we have on the Internet, logged on there, and

changed my password.

--

Steve Riley

steve.riley@microsoft.com

http://blogs.technet.com/steriley

http://www.protectyourwindowsnetwork.com

>

>

> "Anteaus" <Anteaus@discussions.microsoft.com> wrote in message

> news:8303A854-B8AC-4AA9-9B4C-CA68C2374739@microsoft.com...

>> Not a solution, but I 've always thought Windows' default security

>> policies

>> were daft, what with having faddist password-change requirements, yet NO

>> protection against dictionary attack, and NO way of identifying or

>> closing

>> disused accounts.

>>

>> It stands to reason that any system which permits remote access MUST have

>> a

>> limit to the number of password-entry attempts in a given period,

>> otherwise a

>> correct guess is inevitable given enough time. Yet, while windows has

>> this

>> capability it's (inexplicably) turned off by default. Even though

>> turning it

>> on has no significant impact on system useability. Why not, for heavens

>> sake?

>>

>> Disused accounts represent a serious security problem, especially with

>> many

>> sites now granting remote access, thus there may be any number of

>> remotely-accessible accounts lying open for which the user has long-since

>> left the company, but for which the personnel dept just plumb forgot to

>> tell

>> I.T. about. Yet, Windows provides NO way of closing accounts which have

>> not

>> been used for a substantial time, which would seem to be one of the most

>> sensible and basic precautions to take against this occurrence.

>>

>> The other side of this is that despite its laxness in other respects,

>> Windows sets a 42-day password-expiry policy, and worse, does so

>> 'silently'

>> without telling anyone it's done so. This is extremely bad.

>>

>> I've had cases where laptops in overseas locations have unexpectedly

>> demanded a password-change in situations where there was no way to rejoin

>> the

>> domain within the time limit. This effectively 'bricks' the laptop until

>> it

>> can be shipped back to base. Highly embarrassing for me, and could have

>> cost

>> the company an international deal.

>>

>> It's time someone persuaded MS to see sense over these poorly thought-out

>> security policies.

>>

>> 1. Ditch password-expiry, or at least WARN the user that it exists, right

>> from first logon. (timebomb icon in sytem tray?)

>>

>> 2. Set password-lockout (dictionary-attack protection) ON by default.

>>

>> 3. Provide a means to identify/close disused accoutns.

>>

>>

>> Just my two cents worth.

>>