[squid-users] A patch for intercepted/WCCP HTTPS and 409 errors

Scott 3m9n51s2ewut at thismonkey.com
Wed Dec 11 12:49:10 UTC 2019

> On 11/12/19 8:51 pm, Scott wrote:
> > Hi,
> > 
> > I understand that squid does some security checking that the SNI of an 
> > intercepted/WCCP HTTPS requests matches the reverse DNS of the IP of the 
> > connection.  Or something like that.
> Not being able to say precisely what Squid is actually doing shows that
> you are lacking understanding of the processes taking place.
> The security check you are posting about has many secondary consequences
> and side effects to be taken into account. Quite a few people have taken
> a stab at solving these rejections and what we have in Squid right now
> is the best that can be done without significant redesign work (which is
> underway - just very slowly, help welcome).
> This is why we have the squid-dev mailing list for code change
> discussion. If you want to actually help solving false-positives in this
> security check please post there and we who have been working on this
> issue for 10+ years now can discuss what we know about the situation,
> the "gotcha" side effects we have to avoid and ideas for improvement.
> > 
> > However with the prevalence of CDNs and badly configured DNSs and geographic 
> > DNSs, this breaks lots of connections (eg, I can't watch the NHL).
> > 
> > I run Squid on a trusted network and use it primarily for caching and 
> > logging, and so I while I need to run WCCP for some non-proxy capable 
> > devices, I don't need that security check.
> Without that check you cannot call your network a "secure network"
> anymore. The absence of the check opens a nest of security holes for
> attackers to walk right in past all those other protections.
> > 
> > It stops all of those 409 errors occurring.
> > 
> > Because of that I've created some patches that add a new option
> > "host_verify_strict_intercepted" which is off by default.  They are
> > for Squid 4.9.  As this is disabling a security feature of Squid do
> > not apply this patch unless you are prepared for any and all consequences.
> > 
> Please do not spread this around. People who want to really insist on
> allowing virus/malware to spread unchecked around their networks can
> make smaller patches.
> Amos
Hi Amos,

sorry for posting in the wrong forum.  While you're here: I've seen a handful 
of posts about the 409s and the response has been "security".  Fair enough.  

Can you please provide a concrete example of

a) why host_verify_strict is available as a toggle for non-intercepted 
requests, and
b) why intercepted requests don't have this option at all?

I'm suffering from a lack of imagination and I've yet to see any example 
given (and ok, I may have missed one somewhere) and would like one brought to 
my (and other reader's) attention.


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