diff --git a/components/ble/ble_services/ble_nus/ble_nus.c b/components/ble/ble_services/ble_nus/ble_nus.c
index ca77de6..8381f0e 100644
--- a/components/ble/ble_services/ble_nus/ble_nus.c
+++ b/components/ble/ble_services/ble_nus/ble_nus.c
@@ -283,8 +283,8 @@ uint32_t ble_nus_init(ble_nus_t * p_nus, ble_nus_init_t const * p_nus_init)
     add_char_params.char_props.write         = 1;
     add_char_params.char_props.write_wo_resp = 1;
 
-    add_char_params.read_access  = SEC_OPEN;
-    add_char_params.write_access = SEC_OPEN;
+    add_char_params.read_access  = SEC_MITM;
+    add_char_params.write_access = SEC_MITM;
 
     err_code = characteristic_add(p_nus->service_handle, &add_char_params, &p_nus->rx_handles);
     if (err_code != NRF_SUCCESS)
@@ -302,9 +302,9 @@ uint32_t ble_nus_init(ble_nus_t * p_nus, ble_nus_init_t const * p_nus_init)
     add_char_params.is_var_len        = true;
     add_char_params.char_props.notify = 1;
 
-    add_char_params.read_access       = SEC_OPEN;
-    add_char_params.write_access      = SEC_OPEN;
-    add_char_params.cccd_write_access = SEC_OPEN;
+    add_char_params.read_access       = SEC_MITM;
+    add_char_params.write_access      = SEC_MITM;
+    add_char_params.cccd_write_access = SEC_MITM;
 
     return characteristic_add(p_nus->service_handle, &add_char_params, &p_nus->tx_handles);
     /**@snippet [Adding proprietary characteristic to the SoftDevice] */