diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index fbdd504..98a0444 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -22,3 +22,8 @@
 **Vulnerability:** The `ImageLoader` and `VideoURLProvider` scripts validated and upgraded URLs to HTTPS in their string cache for comparisons, but failed to update the actual `VRCUrl` objects used for the download/playback requests. This meant the code *looked* secure (validating strings) but *acted* insecurely (requesting HTTP), creating a false sense of security and leaving users vulnerable to MITM attacks.
 **Learning:** Validating a shadow copy (cache) of data does not secure the source data. When using object wrappers (like `VRCUrl`), modifying the extracted value does not modify the object itself. Security upgrades must be applied to the actual objects used for operations.
 **Prevention:** Explicitly replace or upgrade the source objects (e.g., `predefinedUrls[i] = new VRCUrl(secureUrl)`) when sanitizing inputs, rather than just sanitizing the local variable used for logic checks.
+
+## 2025-05-22 - Prevent Content Spoofing via Fallback Logic
+**Vulnerability:** `FindMatchingUrlIndex` contained a fallback mechanism that blindly mapped unknown URLs from external lists to existing, unrelated `VRCUrl` slots when `useGeneratedUrlData` was enabled. This allowed external configuration to apply arbitrary captions to pre-approved images, creating a spoofing vulnerability.
+**Learning:** Convenience features (like "auto-mapping" or "cyclic assignment" for unmatched items) often undermine strict allowlist enforcement. "Fail Closed" means if an exact match isn't found, the operation must fail, not guess.
+**Prevention:** Remove fallback logic that bypasses exact matching. Ensure that lookups against an allowlist return an error or empty result if the specific item is not found.
diff --git a/Scripts/ImageLoader.cs b/Scripts/ImageLoader.cs
index 092627a..e39dd83 100644
--- a/Scripts/ImageLoader.cs
+++ b/Scripts/ImageLoader.cs
@@ -457,19 +457,6 @@ private int FindMatchingUrlIndex(string urlToFind, int additionalCount = 0)
             }
         }
         
-        // If using generated data, we can use the cyclical assignment
-        if (useGeneratedUrlData)
-        {
-            // Use the next available predefined URL slot (cyclical)
-            int index = (_activeUrlIndices.Length + additionalCount) % urlCount;
-            
-            // Ensure the predefined URL at this index exists
-            if (index < _predefinedUrlStrings.Length && _predefinedUrlStrings[index] != null)
-            {
-                return index;
-            }
-        }
-        
         // Last resort: find any available predefined URL
         // REMOVED for security: preventing content spoofing.
         // If the URL is not found in the predefined list, we should NOT display a random image.
diff --git a/Scripts/VideoURLProvider.cs b/Scripts/VideoURLProvider.cs
index 376a9a4..6bd39c3 100644
--- a/Scripts/VideoURLProvider.cs
+++ b/Scripts/VideoURLProvider.cs
@@ -1040,35 +1040,6 @@ private int FindMatchingUrlIndex(string urlToFind, int additionalCount = 0)
             }
         }
         
-        // If using generated data, we can use the cyclical assignment
-        if (useGeneratedUrlData)
-        {
-            // Use the next available predefined URL slot (cyclical)
-            // Include additionalCount to account for items currently being batched
-            int index = (_activeUrlIndices.Length + additionalCount) % urlCount;
-            
-            // Ensure the predefined URL at this index exists
-            if (index < _predefinedUrlStrings.Length && _predefinedUrlStrings[index] != null)
-            {
-                // Check if this URL is already used
-                string newUrl = _predefinedUrlStrings[index];
-                for (int j = 0; j < _activeUrlIndices.Length; j++)
-                {
-                    int existingIndex = _activeUrlIndices[j];
-                    if (existingIndex < _predefinedUrlStrings.Length && _predefinedUrlStrings[existingIndex] != null)
-                    {
-                        if (_predefinedUrlStrings[existingIndex] == newUrl)
-                        {
-                            Debug.Log($"[VideoURLProvider] URL already exists in playlist, skipping duplicate: {newUrl}");
-                            return -1; // Skip adding duplicate
-                        }
-                    }
-                }
-                
-                return index;
-            }
-        }
-        
         // Last resort: find any available predefined URL
         // REMOVED for security: preventing content spoofing.
         // If the URL is not found in the predefined list, we should NOT display a random video.