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List:       varnish-misc
Subject:    varnish 2.15 - possible security exploit?
From:       scaunter () topscms ! com (Caunter, Stefan)
Date:       2011-02-22 18:03:35
Message-ID: 7F0AA702B8A85A4A967C4C8EBAD6902CF7C23B () TMG-EVS02 ! torstar ! net
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>In message
<AANLkTimzDZXpY=OXb-g3uVj=FurbWpjHweJzLChqrBLg at mail.gmail.com>, Mike
 Franon writes:
>>I was curious does anyone know of any serious security exploits that
>>can use varnish as an open proxy?

>Only if they can reload the Varnish VCL somehow.  Varnish has the
>backends hardcoded in VCL.

>>The reason why I am thinking that some sort of exploit might be going
>>on is, looking at the varnish logs I was seeing some url's for domains
>>we do not even own.

>And what does the log says happen to them ?

>You can probably do something like:

>	if (req.http.host !~ "<regexp matching your domains") {
>		error(755);	/* No need to be civilized here */
>	}

>To prevent them from reaching your backend.


Sure, but maybe we have a non-host specific config for a farm, where if
DNS sends you to varnish, it doesn't check the host header, it just
selects a backend. A regexp matching many domains is avoided in this
case. 

Lets you put varnish in front of many sites without a lot of fuss.

If there's an invalid host, we can simply cache the "don't got" page.

Potential for DoS attack, but hardly specific to varnish.

SC


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