Hi,
By default, self sign cert is used for Surf SOHO admin interface (WebAdmin HTTPS). Thus, when you browse to the WebAdmin page, you will received the warning message . You can bypassing the warning by accepting the self sign cert. For more information on how to bypassing the warning, please refer to the URL below:
If you having security concern regarding to the default self sign cert, you are allow to sign your own certificate and import into the Surf SOHO.
Regarding to the certificate expired date, please make sure you always upgrade the device using the latest firmware and this will give you the latest self sign certificate. You can download the latest device firmware by using the URL below :
Thank You