Re: Guile security vulnerability w/ listening on localhost + port (with fix)

[Christopher Allan Webber <cwebber@dustycloud.org>]

Lizzie Dixon writes:

> Hi,
>
> On 10/11, Christopher Allan Webber wrote:
>> The default in Guile has been to expose a port over localhost to which
>> code may be passed.  The assumption for this is that only a local user
>> may write to localhost, so it should be safe.  Unfortunately, users
>> simultaneously developing Guile and operating modern browsers are
>> vulnerable to a combination of an html form protocol attack [1] and a
>> DNS rebinding attack [2].  How to combine these attacks is published in
>> the article "How to steal any developer's local database" [3].
>
>> 
>> In Guile's case, the general idea is that you visit some site which
>> presumably loads some javascript code (or tricks the developer into
>> pressing a button which performs a POST), and the site operator switches
>> the DNS from their own IP to 127.0.0.1.  Then a POST is done from the
>> website to 127.0.0.1 with the body containing scheme code.  This code is
>> then executed by the Guile interpreter on the listening port.
>
> You don't need to rebind DNS to exploit this bug, or other bugs like
> it. I wrote some details here:
>
> <https://blog.lizzie.io/exploiting-CVE-2016-8606.html>
>
> Best,
>
> Lizzie.

Hi Lizzie!  Thanks for the post.  Interesting to see you figured out how
to do it with a GET request, not just a POST.  So, I guess this will
work from a public site as well?  I'm always a bit fuzzy about what
browsers do and don't allow, but I'm stunned that a browser will let a
request from some http://foo.example/ to http://localhost:37146/, even
for just a GET.  It seems like there are all sorts of daemons you can
exploit that way.

Anyway, thanks for the interesting blogpost, and kudos for using Guile
to write your example!
 - Chris