Port 27017: MongoDB
Port 27017 is the default port for MongoDB databases.
What runs on port 27017
MongoDB listens on TCP 27017 for database connections. It is a popular document database for web apps. Older versions bound to all network interfaces and required no authentication by default.
On a home network
Home servers and Docker setups for self-hosted apps (the UniFi Network application, for example, uses MongoDB internally) may run it. Consumer devices do not.
If port 27017 is reachable from the internet
In early 2017, attackers wiped tens of thousands of internet-exposed MongoDB databases and left ransom notes, and similar campaigns have recurred since. Exposed MongoDB instances have also caused many large data leaks. It should never be reachable from the internet.
How to check whether it is open on your network
Check that MongoDB binds to localhost or a private address and that authorisation is enabled, and that no container or router rule publishes 27017. RECON's Exposure Check tests it from outside.
To find out whether port 27017 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.