Ok I was able to finally figure this out myself. I'll post the answer here in case anyone else ever runs into it. Scanserver is a background app that gets installed by Canon. I have a Canon ImageFORMULA DR-C225 scanner. The latest software package from them (the one designed to work with Mojave) must have included this as a new feature. It basically allows you to press the scan button on the scanner and then automatically start Canon's CaptureOnTouch software. Scanserver listens for incoming requests from the scanner to then initiate the main application. Whether you _should_ allow this app to accept incoming requests is a separate matter from a security standpoint (depends on how much you trust Canon's developers to do this right, how secure your devices and network are, etc.). But this is what scanserver is.