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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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On Windows, having an empty password can improve security

Posted by jpluimers on 2021/08/11

From an interesting twitter thread started by SwitftOnSecurity:

Interesting thought that I need to let sink in for a while before trying it.

Great posts by Aaron

Finding out about and fixing Limited User Account bugs:

More to think about:

  • [WayBack] Table of Contents (Aaron Margosis’ Non-Admin WebLog) – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog
  • [WayBack] Not running as admin… – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog

    To be more secure, users should log on with a Limited (or “Least-privileged”) User account (LUA), and use elevated privileges only for specific tasks that require them.  Linux/Unix users have understood this for a long time

  • [WayBack] Why you shouldn’t run as admin… – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog
    • The #1 reason for running as non-admin is to limit your exposure.
    • My #2 reason for running as non-admin applies to developers.  Developing software as User instead of Admin helps ensure that your software will run correctly on end-users’ systems.
    • My #3 reason applies just to Microsoft personnel, particularly those of us in customer-facing roles.  Hey, y’all!  We need to lead by example.
  • [WayBack] The easiest way to run as non-admin – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog

    Here’s how I set up home computers for friends and relatives:

    • Create a Computer Administrator account called “Admin”.  No password.  (Read on before you flame.)
    • Create a Limited User account for each person who will be using the computer.  No passwords.
    • Enable the Guest account if it is anticipated that visitors may need to go online.

    I instruct all concerned that the Admin account is to be used only for installing software, and to use their individual accounts for all day-to-day use, including web, email, IM, etc.  This has worked quite well for everyone I’ve done this for, and don’t get calls anymore about home pages being hijacked, etc.  Users generally don’t even have to log out.  My 7-year old walks away, the screen saver kicks in, my 3-year old moves the mouse and clicks on his picture (or the frog or whatever it is now) and has his own settings.

    [added 2004.06.22]:  I also like to make the admin desktop noticeably different from normal user desktops, to help prevent accidental use.  For example, use the Windows Classic theme instead of the XP default, set a red background, or a wallpaper that says “For admin use only.  Are you sure you need to be here?”

    OK, I know you’re bursting already:  “No password?!?!  Are you insane?!?!”  Cool down, now.  Starting with Windows XP, a blank password is actually more secure for certain scenarios than a weak password.  By default, an account with a blank password can be used only for logging on at the console.  It cannot be used for network access, and it cannot be used with RunAs.  The user experience of just clicking on your name to log on can’t be beat for simplicity.  If you can trust everyone who has physical access to the computer not to log on as someone else or abuse the admin account, this is a great way to go.  If not, you can always enable passwords.

  • [WayBack] “RunAs” basic (and intermediate) topics – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog

    The Secondary Logon service was first introduced in Windows 2000, and is in Windows XP and Server 2003.  When you start a new process through RunAs, you provide credentials for the account you want the process to run under – for example, the local Administrator account.  Assuming the credentials are valid, the Secondary Logon service then causes several things to happen:

    • creates a new logon session for the specified account, with a new token;
    • ensures that the new process’ token is granted appropriate access to the current window station and desktop (the specifics change somewhat for XP SP2, but aren’t important here);
    • creates a new job in which the new process and any child processes it starts will run, to ensure that the processes are terminated when the shell’s logon session ends (correcting a problem with the NT4 Resource Kit’s SU utility).
  • [WayBack] RunAs with Explorer – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog
  • [WayBack] MakeMeAdmin — temporary admin for your Limited User account – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog

    MakeMeAdmin.cmd invokes RunAs twice, prompting you first for your local admin password, then for your current account password.  The bit that runs as local administrator does the following:

    1. Adds your current account to the local Administrators group (using NET LOCALGROUP, avoiding the problem of needing network credentials to resolve names);
    2. Invokes RunAs to start a new instance of cmd.exe using your current account, which is at this instant a member of Administrators;
    3. Removes your current account from the local Administrators group.

    The result of the second step is a Command Prompt running in a new logon session, with a brand new token representing your current account, but as a member of Administrators.  The third step has no effect on the new cmd.exe’s token, in the same way that adding your account to Administrators does not affect any previously running processes.

  • [WayBack] MakeMeAdmin follow-up – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog

    In my first MakeMeAdmin post, there’s a section called “Objects created while running with elevated privilege,” the main parts of which I’ll recap here:

    Normally, when a user creates a securable object, such as a file, folder, or registry key, that user becomes the “owner” of the object and by default is granted Full Control over it.  Prior to Windows XP, if the user was a member of the Administrators group, that group, rather than the user, would get ownership and full control….  Windows XP introduced a configurable option whether ownership and control of an object created by an administrator would be granted to the specific user or to the Administrators group.  The default on XP is to grant this to the object creator; the default on Windows Server 2003 is to grant it to the Administrators group….

    If I use MakeMeAdmin to install programs, my normal account will be granted ownership and full control over the installation folder, the program executable files, and any registry keys the installation program creates.  Those access rights will remain even when I am no longer running with administrator privileges.  That’s not what I want at all.  I want to be able to run the app, create and modify my own data files, but not to retain full control over the program files after I have installed it.

    I concluded by saying:

    For this reason, I changed the “default owner” setting on my computer to “Administrators group”.

    Today I would like to go further:  If you are going to use the same account for admin and non-admin activities (e.g., with MakeMeAdmin), I strongly recommend that you change the “Default owner” setting on your computer to “Administrators group”.

  • [WayBack] And so this is Vista… – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog

    What becomes of all my earlier non-admin tips, tricks and recommendations vis-à-vis RunAsMakeMeAdminPrivBar and their interactions with IE and Explorer? The short answer is that Vista changes just about everything with respect to running with least privilege.

    Windows Vista makes running as a standard user (non-admin) much more pleasant, feasible and secure than it was on XP. I’m not going to drill into all those improvements here. Instead, the focus of this post is to update my earlier posts about running on XP as a standard user (the “Running as Admin Only When Required” posts in the Table of Contents) as they pertain to Windows Vista. To save some space, I’ll assume you’ve spent at least a little time running Vista.

    rwx—rwx

    > On XP/2003, MakeMeAdmin lets you run as a

    > standard user, and temporarily elevate your

    > standard account to run a selected program

    > with administrative privileges.

    Right.  It doesn’t mean temporarily elevating your administrative account to run elevated, it means temporarily elevating your standard account to run a selected program with administrative privileges in the context of your account.

    > Vista gives you the same ability

    It does not.  Here’s what Vista gives:

    > If you are a member of the Administrators

    > group on Vista

    Exactly.  It means temporarily elevating your administrative account to run elevated.  It doesn’t help your standard account at all.

    > “Run as administrator” serves as a superior

    > substitute. With the default settings, a

    > member of Administrators can use it as a

    > MakeMeAdmin replacement

    No, it is not a substitute, it’s different.  A member of Administrators can use it to temporarily switch context to an administrative account and run elevated in the administrative account.  If the administrator does this to install an application for all users then there’s no real problem, the application gets installed for all users just as it did in XP.  But if the administrator wanted to do this to install an application for the standard user, they can’t do it.  The administrator gets to install the application for one user’s account, which is going to be the administrator’s account, it’s not going to be the standard user’s account.  The standard user doesn’t get the benefit that MakeMeAdmin provided.

    Standard users in Vista still need a MakeMeAdmin tool.

  • [WayBack] Ctrl-C doesn’t work in RUNAS or MakeMeAdmin command shells – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog

    Workaround: 

    Use Ctrl-Break instead.

    [Added, March 9, 2005: While this problem occurs on Windows XP, it does not occur on Server 2003 RTM! ]

  • [WayBack] Follow-up on “Setting color for *all* CMD shells based on admin/elevation status” – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog
  • [WayBack] Running restricted — What does the “protect my computer” option mean? – Aaron Margosis’ Non-Admin, App-Compat and Sysinternals WebLog

    The bottom line is that the app runs with a “restricted token” that basically has these net effects:

    • Group membership:  If you were logged in as a member of Administrators, Power Users, or certain powerful domain groups, the app runs without the benefit of those group memberships.
    • Registry:  The app has read-only access to the registry, including HKEY_CURRENT_USER and HKEY_LOCAL_MACHINE.  The app has no access to HKCU\Software\Policies.
    • File system (assuming NTFS):  The app cannot access the user’s profile directory at all.  That includes “My Documents”, “Temporary Internet Files”, “Cookies”, etc.
    • Privileges:  The app has no system-wide privileges other than “Bypass traverse checking”.

    IE works fairly well this way, but with some odd and annoying problems:

    • You can’t use SSL (https) at all.
    • If you right-click on a hyperlink and choose “Open in New Window”, nothing happens.
    • If you enter a URL in the address bar without “http://” in front of it (e.g., “www.msn.com”), you get an error message like “C:\Documents and Settings\aaronmar\Desktop is not accessible.  Access is denied.”, before IE goes ahead and loads the site anyway.
    • On XP SP2 and on Server 2003, toolbars do not appear where you configured them, if they appear at all.  E.g., PrivBar always needs to be re-enabled; “Links” appears (on my machine) in the upper left, to the left of the menu bar.  (This wasn’t a problem with XP SP1.)

–jeroen

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