malicious requests?

[Alex Haylock]

Are there any known attack vectors that involve appending a period/
full-stop to a sites domain name?

My Django application throws a handful of errors in production every day:

ERROR: Invalid HTTP_HOST header: 'www.example.com.'. You may need to add
u'www.example.com.' to ALLOWED_HOSTS.

(note the trailing period)

Is this malicious behaviour, or just users mistyping the URL?

Also, browsers are clearly treating the final '.' as part of the path
(as these requests are reaching my application), but Django is treating
the '.' as part of the hostname. Which is right?

--
Regards,


Alex

[Markus Holtermann]

Hey Alex,

a trailing . in the host header is valid per RFC 3986: http://tools.ietf.org/html/rfc3986#section-3.2.2:

The rightmost domain label of a fully qualified domain name in DNS may be followed by a single "."

/Markus 

[Alex Haylock]

Thanks Markus.

So, as per the RFC, are 'example.com' and 'example.com.' considered to
be the same domain, or two separate domains?

Are there any security implications if I add 'example.com.' to
ALLOWED_HOSTS to cater for these requests?

Thanks,

Alex.

On 22/12/14 11:52, Markus Holtermann wrote:
> Hey Alex,
>
> a trailing . in the host header is valid per RFC 3986:
> http://tools.ietf.org/html/rfc3986#section-3.2.2:
>
> The rightmost domain label of a fully qualified domain name in DNS
> may be followed by a single "."
>
>
> /Markus
>
> On Monday, December 22, 2014 12:44:25 PM UTC+1, Alex Haylock wrote:
>
> Are there any known attack vectors that involve appending a period/
> full-stop to a sites domain name?
>
> My Django application throws a handful of errors in production every
> day:
>
> ERROR: Invalid HTTP_HOST header: 'www.example.com.'. You may need to
> add

> u'www.example.com <http://www.example.com>.' to ALLOWED_HOSTS.

[Mark Phillips]

Alex,

The trailing period could be from online promotional materials for your site. Someone may have written your URL with the trailing period inside the URL by mistake when the promotional materials were created. It may not be an attack vector from a malicious hacker, but instead, valid users just clicking on a link that contains a URL for your site with the trailing period.

Mark

--
Regards,


Alex

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[Alasdair Nicol]

Hi Alex,

There is no security implication adding 'example.com.' (with trailing
dot) to your ALLOWED_HOSTS setting. There is some more information in
the ALLOWED_HOSTS setting docs.

From https://docs.djangoproject.com/en/1.7/ref/settings/#allowed-hosts

> In previous [<= 1.6.X] versions of Django, if you wanted to also
> allow the fully qualified domain name (FQDN), which some browsers
> can send inthe Host header, you had to explicitly add another
> ALLOWED_HOSTS entry that included a trailing period.

> In Django 1.7, the trailing dot is stripped when performing host
> validation, thus an entry with a trailing dot isn’t required.

cheers,
Alasdair

--
Alasdair Nicol
Developer, MEMSET

mail: alas...@memset.com
web: http://www.memset.com/

Memset Ltd., registration number 4504980.
Building 87, Dunsfold Park, Stovolds Hill, Cranleigh, Surrey, GU6 8TB, UK

[Alex Haylock]

Thanks Alasdair, that's really useful. I'm using v1.6.X in production,
which makes sense based on your email.

Alex.

[Fergus Cameron]

On 22/12/2014, Alasdair Nicol <alas...@memset.com> wrote:
> [ ... ]

> > In Django 1.7, the trailing dot is stripped when performing host
> > validation, thus an entry with a trailing dot isn’t required.

How odd, since the canonical representation would be to add a dot when
one is missing rather than removing it when one is present. I suppose
convention superceeds, oh well.