Why can my app write successfully to HKLM\Software under Vista?

Discussion in 'Windows Vista Security' started by Simon, Feb 28, 2007.

  1. Simon

    Simon Guest

    Everything I read consistently tells me that if UAC is enabled under Vista
    (which it is on my PC) an ordinary application (post-install) which does not
    have any kind of manifest at all, cannot write to the HKLM\Software area of
    the registry. Instead, what is supposed to happen is that Virtualization is
    supposed to redirect the write to


    Well it doesn't. I run my app and change a per-machine setting and it
    updates HKLM\Software no problems. Not only does it look to be updated fine
    if I look at the HKLM\Software area in RegEdit, it still looks OK if I log
    off and log back on using an ordinary (non-admin) account and look at
    HKLM\Software there. If I run my app and change the per-machine setting
    using the other account, sure enough it is changed when I log back on using
    my first account.

    In my first account, there do appear to be some settings in the
    'VirtualStore' area but not many. Most of the settings appear not to be

    What is going on? Any help with this would be much appreciated. The
    documentation I am reading just does not match what I see.

    Simon, Feb 28, 2007
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  2. Simon

    Jesper Guest

    Everything I read consistently tells me that if UAC is enabled under Vista
    First, you are running the app non-elevated right? If so, check the ACL on
    the key in HKLM. There are areas that ordinary users can write to still.
    Virtualization only happens if the user gets an access denied on write.
    Jesper, Feb 28, 2007
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  3. Simon

    Simon Guest

    First, you are running the app non-elevated right?

    That's right. I can run as a non-elevated admin or as a standard user (also
    non-elevated - can they be elevated?). It doesn't make any difference.
    OK - I hadn't got this at all. When my program is installed (for historical
    reasons) the registry key for the application (i.e. the application subkey
    within the company subkey, within HKLM\Software) is given Full Control
    permission to Everyone, and this is inherited by all of its sub-keys. This
    is the reason it's OK to write to these areas? Because they've already been
    set with those permissions at install time?

    So let me get this right - does this mean I don't need to bother about any
    of this UAC stuff? That because I've given everyone permission to write to
    my key anyway, I can carry on as normal with no problems? It just seems
    counter to everything Microsoft seems to be pushing for...

    Simon, Feb 28, 2007
  4. Simon

    Jesper Guest

    check the ACL on
    That's why it is not getting virtualized. If Everyone already has
    permissions the app writes fine to that area.
    It is counter to everything Microsoft has been pushing for. Applications
    should not grant Everyone permission to modify global application settings
    unless they really want any user to be able to modify how the application
    works for any other user. Depending on what data the app stores in the
    registry, that could get really bad. For instance, an app may specify
    settings that cause code to get run. In that case a low-privileged user could
    replace the code that gets run with malicious code. When a high-privileged
    user runs the app the malicious code executes. It depends on the application
    and on whether the computer is multi or single user how bad this is.
    Jesper, Feb 28, 2007
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