diff --git a/dashboard/backend/auth_service.py b/dashboard/backend/auth_service.py
index a321589..cc9d485 100644
--- a/dashboard/backend/auth_service.py
+++ b/dashboard/backend/auth_service.py
@@ -224,14 +224,26 @@ def verify_totp(token: str, secret: str = None):
     if not secret:
         return True  # 2FA not enabled
     totp = pyotp.TOTP(secret)
-    if not totp.verify(token):
+    if not totp.verify(token, valid_window=1):  # Allow 1 time step before/after (±30s)
         return False
 
     def mutator(data):
-        current_ts = int(time.time()) // 30
-        if data.get("last_totp_ts") == current_ts:
+        # Track recently used codes to prevent replay attacks
+        used_codes = data.get("used_totp_codes", [])
+        current_time = int(time.time())
+
+        # Check if this code was already used
+        if token in [code for code, _ in used_codes]:
             return False
-        data["last_totp_ts"] = current_ts
+
+        # Add current code with timestamp
+        used_codes.append((token, current_time))
+
+        # Clean up codes older than 90 seconds (3 time windows)
+        used_codes = [(code, ts) for code, ts in used_codes if current_time - ts < 90]
+
+        # Keep only last 5 codes to limit memory
+        data["used_totp_codes"] = used_codes[-5:]
         return True
 
     return _update_auth_data(mutator)