Firewall kaspersky/avast blocked messages when I'm using a websocket server (socket.io on node.
What can be done?
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I can tell you 100% that Avast for example blocks not only websockets, but from what I see from my Socket.IO app also xhr-polling and other stuff.
This is unacceptable, I've even tested on port 80 and it doesn't work. What an awful piece of software.
this is a list of blocked ports by antiviruses (Dead 2017-07-20)
First rule of Firewall: it can't block what it can't sense.
Does the firewall allow TLS? If so, serve content over WSS instead of WS.
A usual WSS client will open a TLS connection to you (source) and send you this:
GET /demo HTTP/1.1 Upgrade: WebSocket Connection: Upgrade Host: example.com Origin: http://example.com WebSocket-Protocol: sample
The firewall can't detect it because it is over TLS.
A HTTP-CONNECT-WSS client will send you this:
CONNECT example.com:443 HTTP/1.1 Host: example.com
The firewall sees it as yet another HTTP-CONNECT-TLS connection. (source)