Okay, I found 5.4.0 for these cameras here:
http://www.forum.use-ip.co.uk/resources/hikvision-firmware-update-for-ds-2cd2x42fwd-ip-cameras.13/reviews
(backup host: https://mega.nz/#!3c8EwCAZ!7rmX_sbkCReus3JpfEeHFbLperxMnJMdYSTM8MPKy5Y)
(edit: here it is on an official, I think, hikvision site...