[squid-users] questions setting up transparent proxy

[Amos Jeffries]

On 04/01/18 14:09, John Ratliff wrote:
> On 1/3/2018 3:26 PM, Antony Stone wrote:
>> On Wednesday 03 January 2018 at 21:06:42, John Ratliff wrote:
>>
>>> When I try to setup squid as a transparent proxy, I never get any
>>> response from Squid.
>>
>>> When I try a wget request from a server that is being redirected
>>
>> How (and more importantly, where) are you doing the redirect?
>>
>>> Both machines are behind the same firewall. I used
>>> iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to
>>> 10.77.9.120:3128
>>
>> If that firewall is not on the machine running Squid, then that's your 
>> problem.
>>
>>> Traffic flows to the server running squid. I can verify this with
>>> tcpdump. The packets are making it from wget to the server. I just don't
>>> know what happens after that.
>>
>> https://wiki.squid-cache.org/ConfigExamples/Intercept/LinuxRedirect
>>
>> "NOTE: This configuration is given for use *on the squid box*. This is 
>> required
>> to perform intercept accurately and securely. To intercept from a gateway
>> machine and direct traffic at a *separate squid box* use policy routing."
>>
>> https://wiki.squid-cache.org/ConfigExamples/Intercept/IptablesPolicyRoute
>>
>>
>> Antony.
>>
> 
> Thanks. I put squid on the firewall itself. It works for http, but not 
> for https. I get errors with curl and wget.
> 
> $ curl https://debian.org
> curl: (35) error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown 
> protocol
> 
> $ wget https://debian.org
> --2018-01-03 20:02:45--  https://debian.org/
> Resolving debian.org (debian.org)... 5.153.231.4, 128.31.0.62, 
> 130.89.148.14, ...
> Connecting to debian.org (debian.org)|5.153.231.4|:443... connected.
> GnuTLS: An unexpected TLS packet was received.
> Unable to establish SSL connection.
> 
> I made some config changes:
> 
> http_port 3128 intercept
> http_port 3129 intercept ssl-bump generate-host-certificates=on 
> cert=/etc/squid/squid.pem

That should be:

  https_port 3129 intercept ssl-bump generate-host-certificates=on \
    cert=/etc/squid/squid.pem

Note the 's' in https_port.


> 
> sslcrtd_program /usr/lib/squid/ssl_crtd -s /var/lib/ssl_db -M 4MB
> 
> ssl_bump bump all


This instructs Squid to bump before even receiving the client TLS 
handshake - ie. generate a server certificate with zero details to work 
with about what the client wants.
That leads to a LOT of problems and security issues. Please do not do that.

See <https://wiki.squid-cache.org/Features/SslPeekAndSplice> for better 
config examples.


> 
> Here are my PREROUTING nat table rules.
> 
> REDIRECT tcp  --  10.77.9.0/24 anywhere tcp dpt:http redir ports 3128
> REDIRECT tcp  --  10.77.9.0/24 anywhere tcp dpt:https redir ports 3129
> 
> And in the INPUT chain of the filter table:
> 
> ACCEPT tcp  --  10.77.9.0/24 anywhere tcp dpt:3128
> ACCEPT tcp  --  10.77.9.0/24 anywhere tcp dpt:3129
> 
> The server I am on has IP 10.77.9.102.
> 


You appear to be missing the MASQUERADE rule to send packets back to the 
client.

Also the mangle table (*not* filter) rules are important to block 
external traffic directly to those Squid ports without interfering with 
the NAT operations.

<https://wiki.squid-cache.org/ConfigExamples/Intercept/LinuxRedirect>

Amos