full-disclosure - RE: Secure OWA

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Date: Wed, 30 Aug 2006 11:00:18 -0400
From: "Renshaw, Rick \(C.\)" <rrenshaw@...d.com>
To: "Brendan Dolan-Gavitt" <mooyix@...il.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: RE: Secure OWA

-----Original Message-----
From: Brendan Dolan-Gavitt [mailto:mooyix@...il.com] 
Sent: Wednesday, August 30, 2006 9:58 AM
To: Renshaw, Rick (C.)
Cc: Dude VanWinkle; Adriel Desautels; full-disclosure@...ts.grok.org.uk
Subject: Re: [Full-disclosure] Secure OWA

>On 8/30/06, Renshaw, Rick (C.) <rrenshaw@...d.com> wrote:
>>
>>
>> -----Original Message-----
>> From: full-disclosure-bounces@...ts.grok.org.uk
>> [mailto:full-disclosure-bounces@...ts.grok.org.uk] On Behalf Of Dude 
>> VanWinkle
>> Sent: Saturday, August 26, 2006 2:30 PM
>> To: Adriel Desautels
>> Cc: full-disclosure@...ts.grok.org.uk
>> Subject: Re: [Full-disclosure] Secure OWA
>>
>> > The only real fault I know about is the fact that you can guess 
>> > passwords
>> eternally without locking out user accounts.
>>
>> There's two sides to this risk.  If you allow OWA logins to lock out 
>> accounts, and your OWA page is available from anywhere on the 
>> Internet, you are handing an easy DOS tool to anyone that knows the 
>> account names for people on your server.
>>

>Perhaps. But a temporary lockout period would deter brute-force attempts
>while still making an attacker do some work to keep the accounts locked
>(eg, if you have a lockout of 5 minutes, brute forcing is no longer 
>practical, but at the same time, if you want to DoS someone's account 
>you have to keep coming back every 5 minutes. And that increases the 
>risk you'll get caught.)

>-Brendan

My point was not matter which way you go on this issue, there is some risk.
The only thing that you can do is balance one risk against the other and
find the point where you feel comfortable with the risks.  You could
implement something like an exponential backoff wait between failed logins
without lockouts, which would make it more difficult to brute-force the
account, but there are ways around that too.  At the end of the day, you
have to pick which risk you are more comfortable dealing with, brute-force
attacks or DOS attacks.  Personally, I'd take the DOS, because it's better
than allowing passwords to be brute-forced (in my mind).

Rick

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