What is Host "[::]:443" in proxy request?

Question

I have a Firefox configured to use my proxy server. The proxy is receiving a request from Firefox with the header:

CONNECT [::]:443 HTTP/1.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:77.0) Gecko/20100101 Firefox/77.0
Proxy-Connection: keep-alive
Connection: keep-alive
Host: [::]:443

What is the meaning of this? It can't connect to any 3rd party host, so what is the proxy meant to do?

(I've tried a few google searches but the syntax confuses Google...)

score 1 · Accepted Answer · answered Jun 25 '20 at 09:09

1

[::] is the shorthand IPv6 notation of localhost.

:443 is HTTPS.

Your browser is making a request to https://localhost over IPv6.

Usually clients are configured not to use proxies for local connections. It seems like you have a client where this option has been turned off.

answered Jun 25 '20 at 09:09

Gerald Schneider

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Ok but the proxy is configured via IPv4 on a cloud server. Why would firefox make a request to localhost, and send it to a remote proxy? – CaptainCodeman Jun 25 '20 at 09:13
Do you know what I can write in the PAC file so it doesn't forward the localhost requests? – CaptainCodeman Jun 25 '20 at 09:21
I'm not that familiar with proxy.pac, but is this helpful? https://serverfault.com/questions/267280/using-ipv6-addresses-in-proxy-pac – Gerald Schneider Jun 25 '20 at 09:26
I just wrote "if (isPlainHostName(host)) return 'DIRECT';" and it seems to work OK. Thanks for your help. – CaptainCodeman Jun 25 '20 at 10:53

What is Host "[::]:443" in proxy request?

1 Answers1