Port 8008: Chromecast HTTP
Port 8008 is used by Chromecast and Google Cast devices for their local HTTP control interface.
What runs on port 8008
Chromecasts, Google TV devices, Nest speakers and Cast-enabled TVs expose a local HTTP API on TCP 8008 (and 8443 over HTTPS) for setup and device information, alongside the Cast protocol on 8009. It is also a generic alternate HTTP port used by some other software.
On a home network
Chromecasts, Google Nest speakers and displays, Android TVs and TVs with Chromecast built in listen on 8008. Seeing it on those devices inside your home is normal.
If port 8008 is reachable from the internet
Cast devices should never be reachable from the internet. In early 2019 attackers found tens of thousands of Chromecasts exposed through routers with UPnP port forwarding and made them play a video promoting a YouTube channel, and could also rename or reboot them. The fix is to remove the forward, usually by disabling UPnP.
How to check whether it is open on your network
Check your router's UPnP table for mappings to 8008, 8009 or 8443. RECON's Exposure Check shows whether 8008 answers on your public address.
To find out whether port 8008 is open on something in your home, and whether the internet can reach it, the app scans your Wi-Fi from your phone and checks your public address from the outside. It says what it checked and what it could not. Get RECON for iPhone — one-time purchase, no account, nothing leaves the device.