[squid-users] deny_info page not shown

Matus UHLAR - fantomas uhlar at fantomas.sk
Fri Sep 4 14:52:16 UTC 2020

>>> Amos Jeffries <squid3 at treenet.co.nz> wrote:
>>>> CONNECT is a request to open a TCP connection. Delivering an HTTP
>>>> page, or even a URL redirect in response to a TCP connection request
>>>> is completely the wrong type of result.
>>>> Like asking someone to open a door because you have a load of things
>>>> needing to go through it - and they instead throw a basket of apples
>>>> at you. Not want you expected, and more harm than good.
>On 8/28/20 4:31 AM, Matus UHLAR - fantomas wrote:
>> when you ask via HTTP for HTTP page and get HTTP answer, it is different
>> than asking via HTTP for CONNECT and getting CONNECT denied via HTTP.
>> in the latter case it is clear that the request was denied by proxy and
>> since secure content was requested, the insecure response must not be
>> shown.
>> That's the security provided.

On 28.08.20 16:10, Alex Rousskov wrote:
>I believe the above explanations and analogies are rather misleading!
>There are no conceptual or protocol problems with HTTP error responses
>to HTTP CONNECT requests. The browser knows where the response is coming
>from. The browser knows that the response is an error. The browser
>already anticipates and processes some error CONNECT responses specially
>(think proxy authentication). There is no confusion, harm,
>inappropriateness, or some new insecurity here!
>What is actually happening (AFAICT) is that browser folks do not want to
>spend their resources on properly informing the user of the error. There
>are ways to do it, but they all require non-trivial work in a
>controversial area, and browser folks simply do not consider this
>specific use case important enough to support. At the end of the day,
>you are not their customer. They do not want you as their customer. You

This is what I wanted to say. Browsers don't want to show "unsecure" page
gotten via HTTP from proxy, when they expect "secure" content from

They show error instead. I don't want to guess what could happen, if user
entering HTTPS page got HTML from proxy rendered, behaving as if it was the
page from the server.

>While opinions on the underlying causes may differ, the end result is
>still the same -- a forward proxy cannot display an error page to a user
>behind a popular browser in a modern environment (without bumping the
>browser connection first).

Matus UHLAR - fantomas, uhlar at fantomas.sk ; http://www.fantomas.sk/
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