explorer: fix unhandled exception when resolving rule path (#1693)

CHANGELOG.md

@@ -22,6 +22,7 @@
 - linter: skip native API check for NtProtectVirtualMemory #1675 @williballenthin 
 
 ### capa explorer IDA Pro plugin
+- fix unhandled exception when resolving rule path #1693 @mike-hunhoff
 
 ### Development
 

capa/ida/plugin/form.py

@@ -573,10 +573,11 @@ class CapaExplorerForm(idaapi.PluginForm):
 
     def ensure_capa_settings_rule_path(self):
         try:
-            path: Path = Path(settings.user.get(CAPA_SETTINGS_RULE_PATH, ""))
+            path: str = settings.user.get(CAPA_SETTINGS_RULE_PATH, "")
 
             # resolve rules directory - check self and settings first, then ask user
-            if not path.exists():
+            # pathlib.Path considers "" equivalent to "." so we first check if rule path is an empty string
+            if not path or not Path(path).exists():
                 # configure rules selection messagebox
                 rules_message = QtWidgets.QMessageBox()
                 rules_message.setIcon(QtWidgets.QMessageBox.Information)
@@ -594,15 +595,15 @@ class CapaExplorerForm(idaapi.PluginForm):
                 if pressed == QtWidgets.QMessageBox.Cancel:
                     raise UserCancelledError()
 
-                path = Path(self.ask_user_directory())
+                path = self.ask_user_directory()
                 if not path:
                     raise UserCancelledError()
 
-                if not path.exists():
+                if not Path(path).exists():
                     logger.error("rule path %s does not exist or cannot be accessed", path)
                     return False
 
-                settings.user[CAPA_SETTINGS_RULE_PATH] = str(path)
+                settings.user[CAPA_SETTINGS_RULE_PATH] = path
         except UserCancelledError:
             capa.ida.helpers.inform_user_ida_ui("Analysis requires capa rules")
             logger.warning(