diff --git a/backend/app/models/db_models.py b/backend/app/models/db_models.py
index 9a98605a..a2bce361 100644
--- a/backend/app/models/db_models.py
+++ b/backend/app/models/db_models.py
@@ -1,11 +1,11 @@
 # backend/app/models/db_models.py
 """Models SQLAlchemy per a tota la persistència de MiroFish."""
 import uuid
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Optional
 from sqlalchemy import (
     String, Integer, Text, Boolean, DateTime, JSON,
-    ForeignKey, UniqueConstraint
+    ForeignKey
 )
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from ..db import Base
@@ -16,7 +16,7 @@ def _uuid() -> str:
 
 
 def _now() -> datetime:
-    return datetime.utcnow()
+    return datetime.now(timezone.utc)
 
 
 class UserModel(Base):
diff --git a/backend/app/storage/factory.py b/backend/app/storage/factory.py
index 2b3b30f7..642a49b3 100644
--- a/backend/app/storage/factory.py
+++ b/backend/app/storage/factory.py
@@ -1,20 +1,18 @@
 """Selecciona la implementació de StorageService per STORAGE_TYPE."""
-import os
 from .protocol import StorageService
 
 
 def create_storage_service() -> StorageService:
-    storage_type = os.environ.get("STORAGE_TYPE", "local")
+    from app.config import Config
+    storage_type = Config.STORAGE_TYPE
     match storage_type:
         case "azure":
             from .azure_blob import AzureBlobStorage
-            conn_str = os.environ.get("AZURE_STORAGE_CONNECTION_STRING", "")
-            container = os.environ.get("AZURE_STORAGE_CONTAINER", "mirofish")
+            conn_str = Config.AZURE_STORAGE_CONNECTION_STRING
+            container = Config.AZURE_STORAGE_CONTAINER
             if not conn_str:
                 raise RuntimeError("AZURE_STORAGE_CONNECTION_STRING no configurada per STORAGE_TYPE=azure")
             return AzureBlobStorage(conn_str, container)
         case _:
             from .local import LocalFSStorage
-            base = os.environ.get("STORAGE_LOCAL_PATH",
-                                   os.path.join(os.path.dirname(__file__), "../../../uploads"))
-            return LocalFSStorage(base)
+            return LocalFSStorage(Config.STORAGE_LOCAL_PATH)
diff --git a/backend/app/storage/local.py b/backend/app/storage/local.py
index 52b765b9..ccd7ccfe 100644
--- a/backend/app/storage/local.py
+++ b/backend/app/storage/local.py
@@ -1,6 +1,5 @@
 """Adapter de storage per a filesystem local."""
 import io
-import os
 import shutil
 from pathlib import Path
 from .protocol import StorageService
@@ -16,7 +15,9 @@ class LocalFSStorage:
     def _safe_path(self, relative: str) -> Path:
         """Resol el path i valida que estigui dins del base per evitar path traversal."""
         resolved = (self._base / relative).resolve()
-        if not str(resolved).startswith(str(self._base)):
+        try:
+            resolved.relative_to(self._base)
+        except ValueError:
             raise ValueError(f"Path traversal detectat: {relative!r}")
         return resolved
 
@@ -41,6 +42,8 @@ class LocalFSStorage:
             p.unlink()
 
     def delete_prefix(self, prefix: str) -> None:
+        if not prefix or prefix in (".", "/"):
+            raise ValueError("prefix no pot ser buit ni arrel")
         p = self._safe_path(prefix)
         if p.is_dir():
             shutil.rmtree(p)