diff --git a/packages/core/src/services/scripts/GeminiSandbox.cs b/packages/core/src/services/scripts/GeminiSandbox.cs
index 51c57a86b9..2f1bd26cd0 100644
--- a/packages/core/src/services/scripts/GeminiSandbox.cs
+++ b/packages/core/src/services/scripts/GeminiSandbox.cs
@@ -273,7 +273,12 @@ public class GeminiSandbox {
         si.hStdOutput = GetStdHandle(-11);
         si.hStdError = GetStdHandle(-12);
 
-        string commandLine = string.Join(" ", args, 2, args.Length - 2);
+        List<string> quotedArgs = new List<string>();
+        for (int i = 2; i < args.Length; i++) {
+            quotedArgs.Add(QuoteArgument(args[i]));
+        }
+        string commandLine = string.Join(" ", quotedArgs.ToArray());
+
         PROCESS_INFORMATION pi;
         if (!CreateProcessAsUser(hRestrictedToken, null, commandLine, IntPtr.Zero, IntPtr.Zero, true, CREATE_SUSPENDED | CREATE_UNICODE_ENVIRONMENT, IntPtr.Zero, cwd, ref si, out pi)) {
             Console.Error.WriteLine("Failed to create process. Error: " + Marshal.GetLastWin32Error());
@@ -299,6 +304,14 @@ public class GeminiSandbox {
         return (int)exitCode;
     }
 
+    private static string QuoteArgument(string arg) {
+        if (string.IsNullOrEmpty(arg)) return "\"\"";
+        if (arg.IndexOfAny(new char[] { ' ', '\t', '\n', '\v', '\"' }) == -1) return arg;
+
+        string escaped = arg.Replace("\"", "\\\"");
+        return "\"" + escaped + "\"";
+    }
+
     private static int RunInImpersonation(IntPtr hToken, Func<int> action) {
         using (WindowsIdentity.Impersonate(hToken)) {
             return action();
diff --git a/packages/core/src/services/shellExecutionService.ts b/packages/core/src/services/shellExecutionService.ts
index 77d74d2761..d7d30dd44d 100644
--- a/packages/core/src/services/shellExecutionService.ts
+++ b/packages/core/src/services/shellExecutionService.ts
@@ -279,6 +279,14 @@ export class ShellExecutionService {
   ): Promise<ShellExecutionHandle> {
     const sandboxManager =
       shellExecutionConfig.sandboxManager ?? new NoopSandboxManager();
+
+    // Strict sandbox on Windows (network disabled) requires cmd.exe
+    const isStrictSandbox =
+      os.platform() === 'win32' &&
+      shellExecutionConfig.sandboxConfig?.enabled &&
+      shellExecutionConfig.sandboxConfig?.command === 'windows-native' &&
+      !shellExecutionConfig.sandboxConfig?.networkAccess;
+
     const { env: sanitizedEnv } = await sandboxManager.prepareCommand({
       command: commandToExecute,
       args: [],
@@ -302,6 +310,7 @@ export class ShellExecutionService {
             shellExecutionConfig,
             ptyInfo,
             sanitizedEnv,
+            isStrictSandbox,
           );
         } catch (_e) {
           // Fallback to child_process
@@ -316,6 +325,7 @@ export class ShellExecutionService {
       abortSignal,
       shellExecutionConfig.sanitizationConfig,
       shouldUseNodePty,
+      isStrictSandbox,
     );
   }
 
@@ -356,10 +366,18 @@ export class ShellExecutionService {
     abortSignal: AbortSignal,
     sanitizationConfig: EnvironmentSanitizationConfig,
     isInteractive: boolean,
+    isStrictSandbox?: boolean,
   ): ShellExecutionHandle {
     try {
       const isWindows = os.platform() === 'win32';
-      const { executable, argsPrefix, shell } = getShellConfiguration();
+      let { executable, argsPrefix, shell } = getShellConfiguration();
+
+      if (isStrictSandbox) {
+        shell = 'cmd';
+        argsPrefix = ['/c'];
+        executable = 'cmd.exe';
+      }
+
       const guardedCommand = ensurePromptvarsDisabled(commandToExecute, shell);
       const spawnArgs = [...argsPrefix, guardedCommand];
 
@@ -690,6 +708,7 @@ export class ShellExecutionService {
     shellExecutionConfig: ShellExecutionConfig,
     ptyInfo: PtyImplementation,
     sanitizedEnv: Record<string, string | undefined>,
+    isStrictSandbox?: boolean,
   ): Promise<ShellExecutionHandle> {
     if (!ptyInfo) {
       // This should not happen, but as a safeguard...
@@ -700,7 +719,13 @@ export class ShellExecutionService {
     try {
       const cols = shellExecutionConfig.terminalWidth ?? 80;
       const rows = shellExecutionConfig.terminalHeight ?? 30;
-      const { executable, argsPrefix, shell } = getShellConfiguration();
+      let { executable, argsPrefix, shell } = getShellConfiguration();
+
+      if (isStrictSandbox) {
+        shell = 'cmd';
+        argsPrefix = ['/c'];
+        executable = 'cmd.exe';
+      }
 
       const resolvedExecutable = await resolveExecutable(executable);
       if (!resolvedExecutable) {