Windows XP: where to write to registry from IE?

Question

I need to read/write some information in the Windows registry from my BHO. On Windows Vista/7, I create a new key under HKEY_CURRENT_USER\Software\AppDataLow\Software. This works fine, even in protected mode.

However, it does not work on XP. I tried to change the registry to HKEY_CURRENT_USER\Software\Classes\Software or HKEY_CURRENT_USER\Software, no luck.

What is the right registry key to use on Windows XP from a BHO?

IEGetWriteableHKCU does not exist on Windows XP, it was first added in Windows Vista

I suspect you need to IE6 to not cause trouble here. The low privilege paths didn't get added until Vista. — Hans Passant, Feb 23 '12 at 00:27
Under XP, have you tried something like HKCU\Software\YourExtension ? Is the user admin? — Simon Mourier, Feb 28 '12 at 07:43
IEGetWritableHKCU is part of the ieframe.dll which is installed in IE in windows xp. http://xpdll.nirsoft.net/ieframe_dll.html — Alex Mendez, Feb 28 '12 at 17:34
@Alex MS doc says: "Minimum supported client: Windows Vista" (http://msdn.microsoft.com/en-us/library/ie/ms537315%28v=vs.85%29.aspx) — Julien, Feb 28 '12 at 18:32

score 4 · Accepted Answer · answered Feb 28 '12 at 18:57

Before Vista you will have to use a different approach... during installation of the BHO you need to tell Windows/IE which key(s) you want to be writable from the BHO...

There is a whole API family to handle this (supported from WinXP SP2 and up according to MSDN):

IERegisterWritableRegistryKey is used at installation time
IERegisterWritableRegistryValue is used at installation time
IERegCreateKeyEx is used at runtime
IERegSetValueEx is used at runtime

score 3 · Answer 2 · answered Oct 17 '12 at 15:46

IE 7,8,9,(desktop)10 run tabs in "Protected Mode" which limits registry writes to special "writable" section. You need to ask IE for a pointer to it.

(C#)

// C# PInvoke declaration for needed IE method.
[DllImport("ieframe.dll")]
public static extern int IEGetWriteableHKCU(ref IntPtr phKey); 

// ...
        // somewhere inside other method:
        IntPtr phKey = new IntPtr();
        var answer = IEGetWriteableHKCU(ref phKey);
        RegistryKey writeable_registry = RegistryKey.FromHandle(
            new Microsoft.Win32.SafeHandles.SafeRegistryHandle(phKey, true)
        );
        RegistryKey registryKey = writeable_registry.OpenSubKey(RegistryPathString, true);
        if (registryKey == null) {
            registryKey = writeable_registry.CreateSubKey(RegistryPathString);
        }
        registryKey.SetValue("Mode", mode);
        writeable_registry.Close();

See:

About Protected Mode: http://www.codeproject.com/Articles/18866/A-Developer-s-Survival-Guide-to-IE-Protected-Mode

About Enhanced Protected Mode: http://blogs.msdn.com/b/ieinternals/archive/2012/03/23/understanding-ie10-enhanced-protected-mode-network-security-addons-cookies-metro-desktop.aspx

Windows XP: where to write to registry from IE?

2 Answers2