fix(windows): Use ACL instead of chmod

Golang chmod function on windows does not alter ACL's to be 'user only read' it simply changes the read permissions, instead we must use specific windows callouts to set the permissions to be user only preventing ssh from complaining about weak permissions

Author: LaurenceJJones

cmd/ssh/runner_exec_windows.go

@@ -8,6 +8,8 @@ import (
 	"os"
 	"os/exec"
 	"strconv"
+
+	"golang.org/x/sys/windows"
 )
 
 // execSSHSearchPaths are fallback locations for the ssh executable on Windows.
@@ -77,6 +79,59 @@ func RunExec(opts RunOpts) (int, error) {
 	return 0, nil
 }
 
+// setWindowsFileOwnerOnly sets the file's ACL so that only the current user has access.
+// This is required for SSH private keys on Windows, as OpenSSH checks that the key
+// is not accessible by other users.
+func setWindowsFileOwnerOnly(path string) error {
+	// Get the current process token to find the user's SID
+	var token windows.Token
+	proc := windows.CurrentProcess()
+	err := windows.OpenProcessToken(proc, windows.TOKEN_QUERY, &token)
+	if err != nil {
+		return err
+	}
+	defer token.Close()
+
+	// Get the token user (contains the SID)
+	tokenUser, err := token.GetTokenUser()
+	if err != nil {
+		return err
+	}
+	userSID := tokenUser.User.Sid
+
+	// Build an explicit access entry for the current user only (full control)
+	access := []windows.EXPLICIT_ACCESS{
+		{
+			AccessPermissions: windows.GENERIC_ALL,
+			AccessMode:        windows.SET_ACCESS,
+			Inheritance:       windows.NO_INHERITANCE,
+			Trustee: windows.TRUSTEE{
+				TrusteeForm:  windows.TRUSTEE_IS_SID,
+				TrusteeType:  windows.TRUSTEE_IS_USER,
+				TrusteeValue: windows.TrusteeValueFromSID(userSID),
+			},
+		},
+	}
+
+	// Create a new ACL with only our access entry using the public API
+	acl, err := windows.ACLFromEntries(access, nil)
+	if err != nil {
+		return err
+	}
+
+	// Set the security info: owner + DACL, with PROTECTED_DACL to block inheritance
+	secInfo := windows.SECURITY_INFORMATION(windows.OWNER_SECURITY_INFORMATION | windows.DACL_SECURITY_INFORMATION | windows.PROTECTED_DACL_SECURITY_INFORMATION)
+	return windows.SetNamedSecurityInfo(
+		path,
+		windows.SE_FILE_OBJECT,
+		secInfo,
+		userSID,
+		nil,
+		acl,
+		nil,
+	)
+}
+
 func writeExecKeyFilesWindows(opts RunOpts) (keyPath, certPath string, cleanup func(), err error) {
 	if opts.PrivateKeyPEM == "" {
 		return "", "", nil, errors.New("private key required (JIT flow)")
@@ -90,12 +145,13 @@ func writeExecKeyFilesWindows(opts RunOpts) (keyPath, certPath string, cleanup f
 		os.Remove(keyFile.Name())
 		return "", "", nil, err
 	}
-	if err := keyFile.Chmod(0o600); err != nil {
-		keyFile.Close()
+	if err := keyFile.Close(); err != nil {
 		os.Remove(keyFile.Name())
 		return "", "", nil, err
 	}
-	if err := keyFile.Close(); err != nil {
+
+	// Set Windows ACL to restrict access to only the current user
+	if err := setWindowsFileOwnerOnly(keyFile.Name()); err != nil {
 		os.Remove(keyFile.Name())
 		return "", "", nil, err
 	}