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Removing the LAN Manager Hash using Group Policy

Posted on 2012-03-21
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Last Modified: 2012-03-28
I'm gearing up for a security audit and one thing I'd like to try is removing the lm hash file from my machines.  It looks like a simple GP change:

http://support.microsoft.com/kb/299656

I'm just curious how exactly this should work.  From what I've read the LM hash is stored in the c:\windows\system32\config folder in a SAM file.  Once I create the new policy should that file be gone from the machine?  I need a way to confirm that its doing what I think it should be doing.
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by:dave_it
ID: 37747929
My understanding of that setting is that a workstation will not store the LAN Manager hash starting the next time a password is changed.  So it's not an immediate elimination of the LM hash, but it will eventually go away as long as users are forced to change their passwords regularly.
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by:First Last
ID: 37747941
Ouch, the audit is on Wednesday of next week.  Let me dig around and see if I can find more info on that one, I'm testing now as well.  Thanks for the tip!
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by:First Last
ID: 37748261
Are you sure we're talking about the same policy?  I see two similar options:

Network security:  Do not store LAN manager hash value on next password change

and

Network security:  Do not allow storage of passwords and credentials for network authentication

I'm using the second option.
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by:First Last
ID: 37748416
So I've been testing and my plan was to compare the size of the SAM file after making the change.  I discovered that each SAM file is exactly 256kb on every machine I've checked, even on different operating systems.  So I don't think my plan to verify its working would be valid if the file size does not change.

Any way for me to easily check this?
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First Last earned 0 total points
ID: 37757361
As it turns out domain accounts are not stored in the SAM file but in the registry.  The only way I could find to remove stored accounts after the GPO change is manually visiting each station
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Author Closing Comment

by:First Last
ID: 37775752
Found my own solution
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