diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 157d3ed8..8b5c7bc4 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -21,3 +21,8 @@
 **Vulnerability:** `CustomEmployeeManager.Register` accepted arbitrary employee IDs without validation, which were later used directly in `Path.Combine` to construct image loading paths, enabling path traversal (CWE-22).
 **Learning:** Identifiers provided by mods or external sources must be treated as untrusted input and validated before being used in file system operations.
 **Prevention:** Validate input strings that form part of a file path before concatenating them. Reject them if they contain directory traversal characters like `..`, `Path.DirectorySeparatorChar`, `Path.AltDirectorySeparatorChar`, or any invalid filename characters (using `Path.GetInvalidFileNameChars()`).
+
+## 2024-07-29 - Defense-in-depth Path Traversal in Image Loading
+**Vulnerability:** `CustomEmployeeManager.SetPortrait` used `employeeId` to construct file paths for loading images using `Path.Combine`. While the `Register` method validated `employeeId`, direct calls or bypasses (like deserialization) could still pass malicious input, enabling path traversal (CWE-22).
+**Learning:** Relying solely on validation during object registration is insufficient. Methods performing sensitive operations (like file I/O) must independently validate their inputs, especially when handling string identifiers.
+**Prevention:** Implement defense-in-depth by applying path traversal checks (e.g., `IndexOfAny(Path.GetInvalidFileNameChars()) >= 0 || Contains("..")`) directly before file system operations, even if the input was ostensibly validated elsewhere.
diff --git a/src/API/CustomEmployeeManager.cs b/src/API/CustomEmployeeManager.cs
index 9b4512b6..97c06e65 100644
--- a/src/API/CustomEmployeeManager.cs
+++ b/src/API/CustomEmployeeManager.cs
@@ -891,10 +891,19 @@ private static void SetPortrait(Transform card, string employeeId)
 
             string assetsDir = Path.Combine(MelonEnvironment.UserDataDirectory, "ModAssets");
             string? imagePath = null;
-            foreach (var ext in new[] { ".jpg", ".png" })
+
+            // Security: Prevent path traversal attacks by validating employeeId before using it in Path.Combine
+            if (!string.IsNullOrEmpty(employeeId) && employeeId.IndexOfAny(Path.GetInvalidFileNameChars()) < 0 && !employeeId.Contains(".."))
+            {
+                foreach (var ext in new[] { ".jpg", ".png" })
+                {
+                    string candidate = Path.Combine(assetsDir, employeeId + ext);
+                    if (File.Exists(candidate)) { imagePath = candidate; break; }
+                }
+            }
+            else
             {
-                string candidate = Path.Combine(assetsDir, employeeId + ext);
-                if (File.Exists(candidate)) { imagePath = candidate; break; }
+                CrashLog.Log($"[Security] SetPortrait: Invalid characters in employeeId={employeeId}");
             }
 
             if (imagePath != null)