diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..a5e7e4c
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2024-06-18 - Prevent Command Injection via os.startfile on Windows
+**Vulnerability:** Command injection vulnerability via `subprocess.call(['start', filename], shell=True)` in `_open_resource_file`.
+**Learning:** Windows filenames can legally contain shell metacharacters like `&` and `^`. An `os.path.isfile()` check is insufficient to prevent command injection if `shell=True` is used.
+**Prevention:** Prefer using `os.startfile(filename)` over `subprocess.call` with `shell=True` when opening files natively on Windows.
diff --git a/libs/utility_manager.py b/libs/utility_manager.py
index e62d1a5..95de28f 100644
--- a/libs/utility_manager.py
+++ b/libs/utility_manager.py
@@ -43,7 +43,7 @@ def _open_resource_file(self, filename):
 		try:
 			if os.path.isfile(filename):
 				if platform.system() == "Windows":
-					subprocess.call(['start', filename], shell=True)
+					os.startfile(filename)
 				elif platform.system() == "Darwin":
 					subprocess.call(['open', filename])
 				elif platform.system() == "Linux":