RE: To disable SMB packet and secure channel signing enforcement on Windows Server 2003-based domain controllers

From: David LeBlanc (dleblanc_at_mindspring.com)
Date: 05/04/05

  • Next message: vic brown: "Re: To disable SMB packet and secure channel signing enforcement on Windows Server 2003-based domain controllers"
    To: "'Soluk, Kirk'" <kmsoluk@umich.edu>, "'Murad Talukdar'" <talukdar_m@subway.com>, <focus-ms@securityfocus.com>
    Date: Tue, 3 May 2005 15:57:55 -0700
    
    

    I replied privately to Murad, but something I'd like to add -

    Some copiers do run on OS/2 and Linux (though IIRC, samba has been able to
    do signing for a while), so that's probably a good guess.

    As you point out, the attacks enabled by turning down security are severe,
    but if they're in a situation where you're using a DC as a file server, then
    it's probably a very small org. I'd venture that the chances of anyone
    popping up on the network who can launch these attacks are slim, and if a
    hacker does get in, this is unlikely to be the weakest link.

    I wouldn't push back hard right now - I'd try and get a dedicated file
    server ASAP. I'd also want to be sure I had all my other bases covered -
    routine checks for bad passwords, and so on. The problem is that you're not
    going to win this one now. They already have the copier - if this was caught
    pre-purchase, you might be able to win it. An arcane security problem that's
    hard to explain which has a number of preconditions is a losing proposition
    when going up against the boss' shiny new toy.

    One work-around that can be done right away would be to use FTP - all
    Windows servers have a FTP server that can be installed and this would seem
    to be a relatively low-risk option if the files are pushed out without
    authentication. If they use passwords, then FTP is a big step backwards.

    *****************************
    My opinion, and should not be construed as a statement on behalf of my
    employer.
    *****************************

    > -----Original Message-----
    > From: Soluk, Kirk [mailto:kmsoluk@umich.edu]
    > Sent: Tuesday, May 03, 2005 1:09 PM
    > To: Murad Talukdar; focus-ms@securityfocus.com
    > Subject: RE: To disable SMB packet and secure channel signing
    > enforcement on Windows Server 2003-based domain controllers
    >
    > If you disable the SMB signing requirement it means that all
    > your SMB based DC to member communications will be subject to
    > MITM attacks. The primary concern here is your group policy
    > download. In short, the SMB signing requirement provides the
    > assurance that your group policies do not get tampered with
    > in transit. Similarly, disabling the secure channel
    > encryption\signing requirement means that you have no
    > guarantees on all your DC to DC secure channel data (although
    > sensitive information within the secure channel session (e.g.
    > password derived data) will always be encrypted.
    >
    > It makes absolutely no sense to me how an app could be
    > forcing this issue unless it's really old or running on a
    > SAMBA machine. Is that the case?
    >
    > I would push back hard on this. You do not want to take this
    > step backward. You have to be running some pretty old or
    > insecure stuff to have to disable these settings - SMB
    > signing was introduced in NT4 Service Pack 3!
    >
    > Kirk Soluk
    > University of Michigan
    > Information Technology Security Services
    >
    > -----Original Message-----
    > From: Murad Talukdar [mailto:talukdar_m@subway.com]
    > Sent: Tuesday, May 03, 2005 3:32 AM
    > To: focus-ms@securityfocus.com
    > Subject: To disable SMB packet and secure channel signing
    > enforcement on Windows Server 2003-based domain controllers
    >
    > Hi All,
    > We have had arrival of new scanner/printer/copier in office.
    > It uses SMB to scan files to shared folders on our W2003
    > network. In order for it to work however, I have had to do
    > the following;
    >
    > 1. From Administrative Tools open Domain Controller Security Policy 2.
    > Smile 3. Select \Security Settings\Local Policies\Security
    > Options folder. 4. In the details pane, double-click
    > Microsoft network server:
    > Digitally sign communications (always), and then click
    > Disabled to prevent SMB packet signing from being required.
    > 5. Click OK. 6. In the details pane, double-click Domain
    > member: Digitally encrypt or sign secure channel data
    > (always), and then click Disabled to prevent secure channel
    > signing from being required. 7. Click OK.
    >
    > Before that, the scan would fail to be sent to the server in question.
    > What are the implications of this--given that we do not
    > ostensibly use SMB for anything else.
    > I've heard scare stories of SMB man in the middle attacks and
    > was under the impression that this is what these specific
    > security settings were pertaining to but am not sure.
    >
    > There are other options for the scanning ie ftp/email but
    > neither would work as we cannot get approval for cost of ftp
    > server nor can the email system take the file sizes that are
    > often req'd by scans our users make.
    >
    > I can see there will be advice against having shared user
    > folders etc on DC's too but the big boss wants more from less
    > if you see what I mean.
    >
    >
    > Kind Regards
    > Murad Talukdar
    >
    >
    >
    >
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