[squid-users] squid interception

Matus UHLAR - fantomas uhlar at fantomas.sk
Tue Sep 25 11:12:27 UTC 2018

On 25.09.18 12:39, Yann Girardin wrote:
> We have encountered what we think is a strange behavior of Squid when in
> interception.  We know that it's not a bug but made on purpose, but we
> question ourself on the why of this choice.
> We have a firewall that we have configured to redirect all TCP packets
> with the destination port set to 80 to the squid box.  This redirection is
> made by changing the destination IP to the address of the Squid box and

this is wrong way to do interception and it opens door to a security

squid needs to know the destination IP, otherwise it does not know where it
has to connect.

The Host: header is NOT a reliable info, because it can contain false
information. see the vulnerability info:


> destination port to 8080.  On the box, we set up Squid to listen to port
> 9090 in interception mode.  Moreover, we use some DNAT rules to redirect
> the traffic from port 8080 to port 9090.  Yes, we know that we shouldn't
> do that, but "we" includes some third parties.

the proper way to do interception is to forward packets do squid host
without changing the destination I


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