I have an Office Web Apps 2013 farm, unpatched since installation. It was initially installed with SP1 and there are 30 patches released since then. So I'm wondering if I have to apply every patch one by one or I can install only the last one, just as we do for SharePoint CU nowadays. Can anyone share some info on this, references or own experience?
Yes, they're cumulative. Generally they're presented as security patches, but those patches are the 'CU'. Don't forget the patching process for WAC:
- Remove the WAC server from the WAC farm
- Install patch/reboot
- Create a new WAC farm
Repeat steps 1 and 2 for the other WAC servers, but join them to the new farm you created with the first WAC machine to be updated.