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Re: Strange redirection to Cloudflare server with Captcha?

From: Petr Pisar via curl-users <>
Date: Tue, 18 May 2021 20:09:32 +0200

V Mon, May 17, 2021 at 09:27:16PM +0200, Mac-Fly via curl-users napsal(a):
> > You need to compare the whole output (as I showed).
> > Especially debugging of the TLS version, HTTP version,
> > and HTTP headers.
> I am afraid I don't know what to look at exactly.
> But if you look at the snippets I posted: The IP is different already after
> the first lines (and these are the first lines of the log in verbose mode). has 6 different IP addresses. You can you use "--resolve" option to enforce connecting to IP address.

> Then it does no change.

I did not know that.

> One IP points to Cloudfare (the windows one), the
> other does points to audacity (the Linux one).

No. Both belongs to Cloufare. I tried both of them and both of them behave the
same way for me as in your Linux example. Including TLS and HTTP protocol version
and HTTP headers.

> So I _think_ that already at
> that point something was different for an unknown reason. :-/
TLS library, SNI support, maybe other things which cannot be seen from the
log. Or it could be IP addess of the client. (Cloudfare can respond differently
to the same requests arrived from different IP address.)

Just for your reference I have:

$ curl -V
curl 7.76.1 (x86_64-pc-linux-gnu) libcurl/7.76.1 GnuTLS/3.7.1 zlib/1.2.11 libidn2/2.3.0 nghttp2/1.41.0
Release-Date: 2021-04-14
Protocols: dict file ftp ftps http https imap imaps mqtt pop3 pop3s rtsp smtp smtps tftp
Features: AsynchDNS HTTP2 HTTPS-proxy IDN IPv6 Largefile libz NTLM SSL TLS-SRP UnixSockets

I'm also short of ideas.

-- Petr

Received on 2021-05-18