Fix WindowWalker crash (Access Denied) when killing certain protected/elevated processes by Copilot · Pull Request #47397 · microsoft/PowerToys

Copilot · 2026-04-29T08:51:21Z

Summary of the Pull Request

PowerToys Run crashed with Win32Exception (5): Access is denied when using Window Walker to kill an unresponsive window whose process passed the PROCESS_ALL_ACCESS open-handle test but still denied PROCESS_TERMINATE at kill time (e.g., protected processes, certain elevated processes). The fix falls back to elevated taskkill.exe /f in that case, checks the elevation result, handles the process-exit race condition, and adds guard exception handling in the callers to prevent future crashes.

PR Checklist

Detailed Description of the Pull Request / Additional comments

Root cause: TestProcessAccessUsingAllAccessFlag only tests whether OpenProcess(PROCESS_ALL_ACCESS) returns error 5. Some processes (PPL, anti-tamper, certain elevated) pass this check yet deny PROCESS_TERMINATE when Kill() is invoked, throwing an unhandled Win32Exception that crashed PowerToys Run.

Changes:

WindowProcess.KillThisProcess() (Launcher + CmdPal):
- Catches Win32Exception with NativeErrorCode == 5 in the direct-kill path and falls back to elevated taskkill.exe /pid <id> /f, matching the existing IsFullAccessDenied path.
- The return value of OpenInShell is now checked in all call sites (both the IsFullAccessDenied branch and the Win32Exception fallback). If the elevated taskkill fails to launch (e.g. user cancels the UAC prompt), InvalidOperationException is thrown so the caller correctly reports failure instead of treating a non-started kill as success.
- Process object is properly disposed via using.
ContextMenuHelper.KillProcessCommand() (Launcher) and EndTaskCommand.KillProcess() (CmdPal):
- Added catch (ArgumentException) to handle the process-exit race: if the target process exits between the DoesExist validation check and the actual Kill() call, Process.GetProcessById throws ArgumentException. This is now caught and treated as a successful termination (the process is already gone).
- Added catch (Win32Exception) and catch (InvalidOperationException) for any remaining failures (including a declined elevation prompt). These are logged and return false to keep PT Run open rather than crashing.

Validation Steps Performed

Traced the full exception path from the originally reported Win32Exception (5) stack through each fix point.
Verified that the OpenInShell fallback result is checked at all call sites and that failed elevation propagates correctly to the caller.
Verified the ArgumentException process-exit race is covered in both the Launcher and CmdPal callers.

When killing an unresponsive window whose process was not flagged as IsFullAccessDenied (because TestProcessAccessUsingAllAccessFlag passed), Process.Kill() could still throw Win32Exception (error 5) for certain protected/elevated processes. This caused PowerToys Run to crash. - WindowProcess.KillThisProcess() (both launcher and CmdPal): catch Win32Exception with NativeErrorCode == 5 and fall back to elevated taskkill.exe, matching the existing IsFullAccessDenied path. Also properly dispose the Process object via `using`. - ContextMenuHelper.KillProcessCommand() (launcher): catch Win32Exception and InvalidOperationException around KillThisProcess so any remaining failures are logged without crashing PowerToys Run. - EndTaskCommand.KillProcess() (CmdPal): same protective error handling. Agent-Logs-Url: https://github.com/microsoft/PowerToys/sessions/df39f01b-d1e2-413b-9154-0d402084933d Co-authored-by: MuyuanMS <116717757+MuyuanMS@users.noreply.github.com>

Copilot

Pull request overview

This PR updates Window Walker process termination in PowerToys Run and CmdPal to avoid crashes when terminating protected/elevated processes fails with access denied.

Changes:

Adds access-denied fallback from direct Process.Kill to elevated taskkill.exe.
Disposes Process handles after lookup.
Adds caller-side exception guards for kill failures.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
`src/modules/launcher/Plugins/Microsoft.Plugin.WindowWalker/Components/WindowProcess.cs`	Adds direct-kill access-denied fallback to elevated `taskkill`.
`src/modules/launcher/Plugins/Microsoft.Plugin.WindowWalker/Components/ContextMenuHelper.cs`	Adds exception handling around launcher kill command.
`src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WindowWalker/Components/WindowProcess.cs`	Mirrors access-denied fallback for CmdPal Window Walker.
`src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WindowWalker/Commands/EndTaskCommand.cs`	Adds exception handling around CmdPal end-task command.

MuyuanMS · 2026-05-14T08:19:39Z

+            catch (Win32Exception ex)
+            {
+                Log.Exception($"Failed to kill process '{window.Process.Name}' ({window.Process.ProcessID}) of the window '{window.Title}' ({window.Hwnd}).", ex, typeof(ContextMenuHelper));
+                return false;
+            }
+            catch (InvalidOperationException ex)
+            {
+                Log.Exception($"Failed to kill process '{window.Process.Name}' ({window.Process.ProcessID}) of the window '{window.Title}' ({window.Hwnd}).", ex, typeof(ContextMenuHelper));
+                return false;
+            }


Handled in ContextMenuHelper: KillThisProcess is now wrapped with an ArgumentException catch so the process-exit race is treated as success when the PID is already gone.

MuyuanMS · 2026-05-14T08:19:39Z

+        catch (Win32Exception ex)
+        {
+            ExtensionHost.LogMessage(new LogMessage { Message = $"Failed to kill process '{window.Process.Name}' ({window.Process.ProcessID}) of the window '{window.Title}' ({window.Hwnd}): {ex.Message}" });
+            return false;
+        }
+        catch (InvalidOperationException ex)
+        {
+            ExtensionHost.LogMessage(new LogMessage { Message = $"Failed to kill process '{window.Process.Name}' ({window.Process.ProcessID}) of the window '{window.Title}' ({window.Hwnd}): {ex.Message}" });
+            return false;
+        }


Applied the same fix in the CmdPal WindowWalker EndTaskCommand: ArgumentException from the process-exit race is now swallowed so an already-exited process is treated as a successful end-task.

MuyuanMS · 2026-05-14T08:19:40Z

+                    string killTree = killProcessTree ? " /t" : string.Empty;
+                    Helper.OpenInShell("taskkill.exe", $"/pid {(int)ProcessID} /f{killTree}", null, Helper.ShellRunAsType.Administrator, true);


Updated the launcher WindowProcess fallback path to check Helper.OpenInShell. If the elevated taskkill launch fails, it now throws InvalidOperationException so the caller reports failure instead of incorrectly returning success.

MuyuanMS · 2026-05-14T08:19:39Z

+                var killTree = killProcessTree ? " /t" : string.Empty;
+                ExplorerInfoResultCommand.OpenInShell("taskkill.exe", $"/pid {(int)ProcessID} /f{killTree}", null, ExplorerInfoResultCommand.ShellRunAsType.Administrator, true);


Applied the same elevated-fallback handling in the CmdPal WindowProcess: OpenInShell is now checked and a failed elevated launch raises InvalidOperationException so the kill is not reported as successful.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

MuyuanMS · 2026-05-14T08:31:58Z

@copilot please re-review the latest changes.

Copilot · 2026-05-14T08:41:05Z

@copilot please re-review the latest changes.

The latest changes in commit bef5a36 look correct. All four issues from the review are properly addressed:

Process-exit race (ArgumentException): Caught in both ContextMenuHelper.KillProcessCommand() and EndTaskCommand.KillProcess(). Since the process is already gone, falling through to the success return is the right behavior.
OpenInShell return value: Checked in all three call sites across both WindowProcess implementations (IsFullAccessDenied path and the Win32Exception fallback catch). A false return throws InvalidOperationException, which propagates to the caller's handler.
ArgumentException propagation: When Process.GetProcessById throws inside KillThisProcess, it correctly propagates uncaught to the callers where it is handled.
Process disposal: using applied in both WindowProcess implementations.

Initial plan

bc662ed

Copilot AI assigned Copilot and MuyuanMS Apr 29, 2026

Copilot started work on behalf of MuyuanMS April 29, 2026 09:16 View session

Copilot AI linked an issue Apr 29, 2026 that may be closed by this pull request

PowerToys Run ran into an issue while trying to kill an unresponsive window #42803

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Copilot AI changed the title ~~[WIP] Fix PowerToys Run issue killing unresponsive window~~ Fix WindowWalker crash (Access Denied) when killing certain protected/elevated processes Apr 29, 2026

Copilot finished work on behalf of MuyuanMS April 29, 2026 09:25

Copilot AI requested a review from MuyuanMS April 29, 2026 09:25

niels9001 added the Product-Command Palette Refers to the Command Palette utility label Apr 29, 2026

MuyuanMS requested a review from Copilot May 14, 2026 03:09

Copilot started reviewing on behalf of MuyuanMS May 14, 2026 03:10 View session

Copilot AI reviewed May 14, 2026

View reviewed changes

Address review: handle process-exit race and check elevation result

bef5a36

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot started work on behalf of MuyuanMS May 14, 2026 08:38 View session

Copilot finished work on behalf of MuyuanMS May 14, 2026 08:42

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Fix WindowWalker crash (Access Denied) when killing certain protected/elevated processes#47397

Fix WindowWalker crash (Access Denied) when killing certain protected/elevated processes#47397
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		string killTree = killProcessTree ? " /t" : string.Empty;
		Helper.OpenInShell("taskkill.exe", $"/pid {(int)ProcessID} /f{killTree}", null, Helper.ShellRunAsType.Administrator, true);

		var killTree = killProcessTree ? " /t" : string.Empty;
		ExplorerInfoResultCommand.OpenInShell("taskkill.exe", $"/pid {(int)ProcessID} /f{killTree}", null, ExplorerInfoResultCommand.ShellRunAsType.Administrator, true);

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Summary of the Pull Request

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Copilot AI commented Apr 29, 2026 •

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