<div dir="ltr">De facto, some "big guys" already use underscores in their host names:<br><br>sasha@kernel.home:~$ host <a href="http://cow_fb_cdn0-a.akamaihd.net">cow_fb_cdn0-a.akamaihd.net</a> <br><a href="http://cow_fb_cdn0-a.akamaihd.net">cow_fb_cdn0-a.akamaihd.net</a> is an alias for <a href="http://cow_fb_cdn0-a.akamaihd.net.edgesuite.net">cow_fb_cdn0-a.akamaihd.net.edgesuite.net</a>.<br><a href="http://cow_fb_cdn0-a.akamaihd.net.edgesuite.net">cow_fb_cdn0-a.akamaihd.net.edgesuite.net</a> is an alias for <a href="http://a1877.g.akamai.net">a1877.g.akamai.net</a>.<br><a href="http://a1877.g.akamai.net">a1877.g.akamai.net</a> has address 104.73.160.114<br><a href="http://a1877.g.akamai.net">a1877.g.akamai.net</a> has address 104.73.160.64<br>sasha@kernel.home:~$<br><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Nov 17, 2016 at 12:21 PM, Thomas Ward <span dir="ltr"><<a href="mailto:teward@dark-net.net" target="_blank">teward@dark-net.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Correct me if I am wrong but the discussion of underscores in DNS does not apply to hostnames. The discussion referenced states as such, and only touches on underscores as a part of DNS attributes and internals, not as part of hostnames. It even says as such that hostnames are *not permitted* to have underscores.<br>
<br>
By extension of that, should not the Host header should be a hostname or a requested hostname and therefore obey the requirements for a Hostname at the bare minimum?<br>
<br>
<br>
*Sent from my iPhone. Please excuse any typos, as they are likely to happen by accident.*<br>
<div class="HOEnZb"><div class="h5"><br>
> On Nov 17, 2016, at 12:10, Maxim Dounin <<a href="mailto:mdounin@mdounin.ru">mdounin@mdounin.ru</a>> wrote:<br>
><br>
> Hello!<br>
><br>
>> On Wed, Nov 16, 2016 at 06:36:12PM -0600, Aleksandr Kupriyanov wrote:<br>
>><br>
>> <<a href="http://www.google.com/url?q=http%3A%2F%2Fwww.instartlogic.com%2F&sa=D&sntz=1&usg=AFrqEzc4puDXYOgyifEWrSJrJIfW1sViFg" rel="noreferrer" target="_blank">http://www.google.com/url?q=<wbr>http%3A%2F%2Fwww.instartlogic.<wbr>com%2F&sa=D&sntz=1&usg=<wbr>AFrqEzc4puDXYOgyifEWrSJrJIfW1s<wbr>ViFg</a>><br>
><br>
>> # HG changeset patch<br>
>> # User Aleksandr Kupriyanov <<a href="mailto:sasha@instartlogic.com">sasha@instartlogic.com</a>><br>
>> # Date 1479340749 21600<br>
>> # Node ID af947b854971993f318417c70c3818<wbr>147b320a0d<br>
>> # Parent 6a26016e9a138102798a7ec3e74747<wbr>fbd6018f82<br>
>> Add directive to allow underscores in hostnames<br>
>><br>
>> Two equivalent requests generate different responses:<br>
>><br>
>> 1. ---------------<br>
>> GET <a href="http://host_1.home/" rel="noreferrer" target="_blank">http://host_1.home/</a> HTTP/1.1<br>
>> Host: host_1.home<br>
>> ...<br>
>> HTTP/1.1 400 Bad Request<br>
>> Server: nginx/1.X.XX<br>
>> ------------------<br>
>><br>
>> 2. ---------------<br>
>> GET / HTTP/1.1<br>
>> Host: host_1.home<br>
>> ...<br>
>> HTTP/1.1 200 OK<br>
>> Server: nginx/1.X.XX<br>
>> ------------------<br>
>><br>
>> To avoid that a new directive is proposed:<br>
>><br>
>> Syntax: underscores_in_hostname on | off;<br>
>> Default: underscores_in_headers off;<br>
>> Context: http, server<br>
>><br>
>> Enables or disables the use of underscores in host names of<br>
>> client request line.<br>
>><br>
>> See a discussion about underscores in DNS here:<br>
>> <a href="http://domainkeys.sourceforge.net/underscore.html" rel="noreferrer" target="_blank">http://domainkeys.sourceforge.<wbr>net/underscore.html</a><br>
><br>
> Shouldn't we just allow underscores in<br>
> ngx_http_parse_request_line() instead? It doesn't looks like<br>
> there are reasons to keep the test that strict.<br>
><br>
> In case of underscores_in_headers there a clear security reason:<br>
> headers are exposed via the HTTP_* variables in CGI, and via<br>
> $http_* variables in nginx itself, and this makes headers with<br>
> underscores indistinguishable from ones with dash, and creates an<br>
> attack vector.<br>
><br>
> I don't see such a problem with underscores in hostname when it's<br>
> passed via the request line - especially keeping in mind that we<br>
> don't enforce such a limitation via the Host header.<br>
><br>
> --<br>
> Maxim Dounin<br>
> <a href="http://nginx.org/" rel="noreferrer" target="_blank">http://nginx.org/</a><br>
><br>
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