[squid-dev] Allowing the admin to decide if a specific DNS+ip is ok for caching.

Eliezer Croitoru eliezer at ngtech.co.il
Fri Jul 20 08:56:17 UTC 2018


So we will try to make the whole environment more secure rather than more "profitable".
I think that in general it's a good concept and doesn't sound like some "OCD" alike issue.

I will try to write an article about 4.1 release with this point in mind.


* I do not really care if someone will think or thinks that my articles are profiting me in any way....

Eliezer Croitoru
Linux System Administrator
Mobile: +972-5-28704261
Email: eliezer at ngtech.co.il

-----Original Message-----
From: squid-dev [mailto:squid-dev-bounces at lists.squid-cache.org] On Behalf Of Amos Jeffries
Sent: Thursday, July 19, 2018 10:46 AM
To: squid-dev at lists.squid-cache.org
Subject: Re: [squid-dev] Allowing the admin to decide if a specific DNS+ip is ok for caching.

On 19/07/18 04:56, Eliezer Croitoru wrote:
> Hey Squid-Dev’s,
> Currently Squid-Cache forces Host Header Forgery on http and https requests.
> -          https://wiki.squid-cache.org/KnowledgeBase/HostHeaderForgery

Forces? no. Prevents.

> Squid is working properly or “the best” when the client and the proxy
> use the same DNS service.
> In the past I have asked about defining a bumped connection as secured
> and to disable host header forgery checks on some of these.

Having a connection be bumped does not mean the requests decrypted from
that connection are meant for that server. DONT_VERIFY_PEER and such
false "workaround" are still very common things for admin to do.

A client or intermediary can as easily forge the SNI value on TLS setup
as a Host header in plain-text HTTP. The resulting problems in both
cases are the same.

> The conditions are:
> -          Squid validates that the server certificate is valid against
> the local CA bundles (an admin can add or remove a certificate manually
> or automatically)
> -          The admin defines an external tool that verifies and/or
> allows host header forgery to be disabled per request.
> I am in the middle of testing 4.1 and wondering what is expected from
> 4.1 regarding host header forgery.
> Was there any change of policy?

No changes from Squid-3 are expected in terms of these checks. There may
be changes in TLS handling which decrypt more (or less) requests.

Any requests which *are* decrypted, the initial CONNECT (from SNI) are
expected to be verified.
 TPROXY / NAT intercepted traffic is verified against the against the
dst-IP of the intercepted client TCP connection.
 Bumped and non-intercepted traffic (in strict verify mode) against the
server-IP from initial client CONNECT tunnel.

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