Why is Syncthing trying to connect to various IP addresses?

Software & Web Applications
1

I installed Syncthing on my Win 11 Pro PC but haven’t made any use of it yet. But Malwarebytes keeps popping up to say it has blocked it from connecting to various IP addresses that it says are dangerous.

I’ve set it to not automatically update, so why is it trying to talk to the IP addresses?

When I try to see what the addresses are Malwarebytes blocks them saying they are dangerous.

Can anyone tell me why it is doing this?

Some of the addresses are

23.137.105.248
104.223.84.81
31.40.204.161

Sorry if this is a stupid question, but I couldn’t find an answer. One address appears to be a Tor node, but I don’t know what this means or why Syncthing is trying to talk to it?

2

Syncthing has “global announce servers” also known as internet relays to help your devices connect, at the very least passing each others’ IP and port. You can choose to disable those in order to rely on purely broadcast based and last-known-address based connections. I’m not certain whether you can just manually put in the other PCs IP address to connect to. You have to know the long and randomly generated ID of a syncthing device to get its current connection info from the announce servers, so it isn’t really a privacy or security risk.

3

Thank you.

I only ever want to use Syncthing on my own network. Is there a way to stop it looking externally?

4

Just block syncthing access to internet with firewall.

5

I meant within Syncthing?

6

You cant. Its hardcoded. Firewall is your only option, or edit the hosts file and sinkhole all the IPs.

7

You can disable “global discovery” inside of the syncthing settings.

1 Like
8

It will still try to talk outside of local network.

9

You can disable this in the Syncthing settings. Go to Actions → Settings → Connections and uncheck the Global Discovery

That is not true. This topic is in their documentation Security Principles — Syncthing documentation

10

It doesnt matter what they say. I have those options disabled and my syncthing block rule still shows blocked traffic.

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11

You should file a bug report so that it gets fixed.