[Security][Hosts] Remove open method lookup and hardcode the notepad to open host editor (#46194)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
**This is a security issue fix**

In Hosts Editor module, we support to open the hosts file through user's
default editor.
The way to find the editor is that we will read a registry key and use
the value as a parameter to call Process.Start.

In most case, it works well. But Hosts editor module will launch as
admin permission. But the registry value can be modified in user 's
permission (without UAC request).

So, the malware may change the registry value and if user click the open
button. May call the dangerous command which written in registry.


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## PR Checklist

- [x] Closes: #46195
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issues) -->
- [ ] **Communication:** I've discussed this with core contributors
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- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
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and link it here: #xxx

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---------

Co-authored-by: Yu Leng (from Dev Box) <yuleng@microsoft.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

src/modules/Hosts/HostsUILib/Helpers/HostsService.cs

@@ -16,7 +16,6 @@ using System.Threading.Tasks;
 using HostsUILib.Exceptions;
 using HostsUILib.Models;
 using HostsUILib.Settings;
-using Microsoft.Win32;
 
 namespace HostsUILib.Helpers
 {
@@ -223,64 +222,17 @@ namespace HostsUILib.Helpers
 
         public void OpenHostsFile()
         {
-            var notepadFallback = false;
-
             try
             {
-                // Try to open in default editor
+                var notepadPath = Path.Combine(
-                var key = Registry.ClassesRoot.OpenSubKey("SystemFileAssociations\\text\\shell\\edit\\command");
+                    Environment.GetFolderPath(Environment.SpecialFolder.Windows),
-                if (key != null)
+                    "System32",
-                {
+                    "notepad.exe");
-                    var commandPattern = key.GetValue(string.Empty).ToString(); // Default value
+                Process.Start(new ProcessStartInfo(notepadPath, HostsFilePath));
-                    var file = null as string;
-                    var args = null as string;
-
-                    if (commandPattern.StartsWith('\"'))
-                    {
-                        var endQuoteIndex = commandPattern.IndexOf('\"', 1);
-                        if (endQuoteIndex != -1)
-                        {
-                            file = commandPattern[1..endQuoteIndex];
-                            args = commandPattern[(endQuoteIndex + 1)..].Trim();
-                        }
-                    }
-                    else
-                    {
-                        var spaceIndex = commandPattern.IndexOf(' ');
-                        if (spaceIndex != -1)
-                        {
-                            file = commandPattern[..spaceIndex];
-                            args = commandPattern[(spaceIndex + 1)..].Trim();
-                        }
-                    }
-
-                    if (file != null && args != null)
-                    {
-                        args = args.Replace("%1", HostsFilePath);
-                        Process.Start(new ProcessStartInfo(file, args));
-                    }
-                    else
-                    {
-                        notepadFallback = true;
-                    }
-                }
             }
             catch (Exception ex)
             {
-                LoggerInstance.Logger.LogError("Failed to open default editor", ex);
+                LoggerInstance.Logger.LogError("Failed to open notepad", ex);
-                notepadFallback = true;
-            }
-
-            if (notepadFallback)
-            {
-                try
-                {
-                    Process.Start(new ProcessStartInfo("notepad.exe", HostsFilePath));
-                }
-                catch (Exception ex)
-                {
-                    LoggerInstance.Logger.LogError("Failed to open notepad", ex);
-                }
             }
         }