Re: NT Login Default Folder Vulnerability

From: Russ (Russ.Cooperat_private)
Date: Tue Jul 06 1999 - 22:31:26 PDT

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    >I just tested this on NT4 SP4 and this is real! Policies are, for the
    >most part, obsolete....
    
    I'm not sure what the reference to policies being obsolete is supposed
    to mean. They could be by-passed, but there are ways to prevent this.
    
    1. Remove any file named explorer.exe, taskmgr.exe, etc... during a
    login script. Since login scripts still process prior to loading the
    desktop (or any of the renamed executables), its possible to eliminate
    any trojans that might be present.
    
    2. Place a copy of the "official" files (explorer, etc...) into the
    user's home directory and then ACL them for Administrator's modification
    only, thereby preventing this from being an issue in many profiled
    environments.
    
    3. I haven't tried this, but it should be possible to prevent, by
    policy, execution of the given executables from the user's home
    directory (while still permitting them to be run from %systemroot%).
    Their desktop will hang, I would assume, as a result of them placing an
    excluded filename in their home directory.
    
    Note these are only workarounds, and may not work if the user has access
    to the user's home directory (%systemroot% if no directory specified) in
    situations where ACLs can be usurped (e.g. a user is a Local
    Administrator and can boot to the machine, rather than the domain).
    
    Clearly there's a large and real issue here, but just as clearly,
    Policies aren't, for the most part, obsolete.
    
    You may also prefer to use CMD.EXE instead of COMMAND.COM to test this,
    just to be safe and ensure you'll be able to recover. On a funny note, I
    followed the original poster's suggestion of renaming calc.exe as
    explorer.exe and rebooted...;-]...needless to say there was a momentary
    look of shock on my face as I tried to remember what to do to get the
    real explorer back on my desktop...;-] (in case you find yourself in
    this situation, CTRL-ALT-DEL, Task Manager, File, Run,
    %systemroot%\explorer.exe restores your desktop)
    
    Cheers,
    Russ - NTBugtraq Editor
    http://ntbugtraq.ntadvice.com/archives
    



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