ATSS showed 'CBTC applied EB due to train doors opened while moving.' TC informed that the 'A' side cab door was loose. Thereafter, TC closed the cab door and confirmed that cab door was no longer loose. ~~~~~ 3511 ATSS showed 'CBTC applied EB due to train doors opened while moving. TC informed that the 'A' sidecab door was loose. Thereafter, TC closed the cab door and confirmed that cab door was no longer loose. CE checked N , depot to check (OE).  3511 A/S cab door checked able to close & latched properly. No sign of looseness found. Cab door handle was found to be slightly loose & retightened the screw. Security/function check - OK.  Abdillah 44472