Squid Proxy

Sample squid proxy and Dockerfile demonstrating various confg modes.

The Dockerfile and git image compiles squid with ssl_crtd enabled which allows for SSL intercept and rewrite.

The corresponding docker image is on dockerhub:

https://hub.docker.com/r/salrashid123/squidproxy/

The image has no entrypoint set to allow you to test and run different modes.

To run the image, simply invoke a shell in the container and start squid in the background for the mode you are interested in:

docker run  -p 3128:3128 -ti docker.io/salrashid123/squidproxy /bin/bash

Also see

Squid proxy cluster with ssl_bump on Google Cloud

FORWARD

Explicit forward proxy mode intercepts HTTP traffic and uses CONNECT for https.

Launch:

$ /apps/squid/sbin/squid -NsY -f /apps/squid.conf.forward &

then in a new window run both http and https calls:

$ curl -v -x localhost:3128 -L http://www.bbc.com/

$ curl -v -x localhost:3128 -L https://www.bbc.com/

you should see a GET and CONNECT logs within the container

$ cat /apps/squid/var/logs/access.log
1530946085.554    108 172.17.0.1 TCP_MISS/200 224517 GET http://www.bbc.com/ - HIER_DIRECT/151.101.52.81 text/html
1530946085.556    451 172.17.0.1 TCP_TUNNEL/200 3909 CONNECT www.bbc.com:443 - HIER_DIRECT/151.101.52.81 -

You can also setup allow/deny rules for the domain:

see squid.conf.allow_domains

If you want to use https_port, use squid.conf.https_port. For https_port see curl options like this:

curl -v --proxy-cacert CA_crt.pem -x https://squid.yourdomain.com:3128 https://www.yahoo.com/ (you will need to add 127.0.0.1 squid.yourdomain.com to your /etc/hosts as an override)

HTTPS INTERCEPT

In this mode, an HTTPS connection actually terminates the SSL connection on the proxy, then proceeds to download the certificate for the server you intended to visit. The proxy server then issues a new certificate with the same specifications of the site you wanted to visit and sends that down.

Essentially, the squid proxy is acting as man-in-the-middle. Ofcourse, you client needs to trust the certificate for the proxy but if not, you will see a certificate warning.

http://www.squid-cache.org/Doc/config/ssl_bump/

Here is the relevant squid conf setting to allow this:

squid.conf.intercept:

# Squid normally listens to port 3128
visible_hostname squid.yourdomain.com

http_port 3128 ssl-bump generate-host-certificates=on cert=/apps/CA_crt.pem key=/apps/CA_key.pem

always_direct allow all

acl excluded_sites ssl::server_name .wellsfargo.com
ssl_bump splice excluded_sites
ssl_bump bump all

sslproxy_cert_error deny all
sslcrtd_program /apps/squid/libexec/ssl_crtd -s /apps/squid/var/lib/ssl_db -M 4MB sslcrtd_children 8 startup=1 idle=1

The configuration above will insepct all SSL traffic but only splice traffic to wellsfargo.com to view its intended SNI (server_name). You can use the splice capability to apply ACL rules against without inspecting.

SslPeekAndSplice

Launch

$ docker run  -p 3128:3128 -ti docker.io/salrashid123/squidproxy /apps/squid/sbin/squid -NsY -f /apps/squid.conf.intercept

then in a new window, try to access a secure site

$ wget https://raw.githubusercontent.com/salrashid123/squid_proxy/master/CA_crt.pem

$ curl -v --proxy-cacert CA_crt.pem --cacert CA_crt.pem -x localhost:3128  https://www.httpbin.org

you should see the proxy intercept and recreate httpbin's public certificate:

* Server certificate:
*  subject: CN=www.httpbin.org
*  start date: Dec  6 13:24:37 2019 GMT
*  expire date: Jul 28 13:24:37 2021 GMT
*  subjectAltName: host "www.httpbin.org" matched cert's "www.httpbin.org"
*  issuer: C=US; ST=California; L=Mountain View; O=Google; OU=Enterprise; CN=MyCA   <<<<<<<<<<<<<<<<<<
*  SSL certificate verify ok.
> GET / HTTP/1.1
> Host: www.httpbin.org
> User-Agent: curl/7.66.0
> Accept: */*

note the issuer is the proxy's server certificate (CA_crt.pem), NOT httpbin's official public cert

Now try to access www.wellsfargo.com. The configuration above simply views the SNI information without snooping on the data

$ curl -vvvv --proxy-cacert CA_crt.pem --cacert CA_crt.pem -x localhost:3128  https://www.wellsfargo.com

* Server certificate:
*  subject: businessCategory=Private Organization; jurisdictionC=US; jurisdictionST=Delaware; serialNumber=251212; C=US; ST=California; L=San Francisco; O=Wells Fargo & Company; OU=DCG-PSG; CN=www.wellsfargo.com
*  start date: Feb  8 00:00:00 2019 GMT
*  expire date: Feb  8 12:00:00 2021 GMT
*  subjectAltName: host "www.wellsfargo.com" matched cert's "www.wellsfargo.com"
*  issuer: C=US; O=DigiCert Inc; CN=DigiCert Global CA G2                            <<<<<<<<<<<<<<<<<<
*  SSL certificate verify ok.
> GET / HTTP/1.1
> Host: www.wellsfargo.com
> User-Agent: curl/7.66.0
> Accept: */*

Also see: How to Add DNS Filtering to Your NAT Instance with Squid

Content Adaptation

content_adaptation/ allows you to not just intercept SSL traffic, but to actually rewrite the content both ways.

CACHE

Has cache enabled for HTTP traffic

Launch

First init the cache directories

$ /apps/squid/sbin/squid -z -f /apps/squid.conf.cache

then
$ /apps/squid/sbin/squid -NsY -f /apps/squid.conf.cache

note: the step to init the cache directory should be in the dockerfile; i've got a todo: to figure out why the setting in the dockerfile itself to init doens't work.

Run two requests

$ curl -k -x localhost:3128 -L http://www.bbc.com

$ curl -k -x localhost:3128 -L http://www.bbc.com

First request is a TCP_MISS, the second is TCP_MEM_HIT

$ cat /apps/squid/var/logs/access.log
1489070394.303    748 172.17.0.1 TCP_MISS/200 207886 GET http://www.bbc.com/ - HIER_DIRECT/151.101.52.81 text/html
1489070395.767      1 172.17.0.1 TCP_MEM_HIT/200 207721 GET http://www.bbc.com/ - HIER_NONE/- text/html

Basic Auth

Enables squid proxy in default mode but requires a username password for the proxy

user: user1
password:user1

Launch:

$ /apps/squid/sbin/squid -NsY -f /apps/squid.conf.basicauth &

$ curl -x localhost:3128 --proxy-user user1:user1 -L http://www.yahoo.com

THe specific config for this mode:

squid.conf.basicaith

#user1:user1
#/apps/squid/squid_passwd:  user1:aje5nXwboMxWY
auth_param basic program /apps/squid/libexec/basic_ncsa_auth /apps/squid_passwd
acl authenticated proxy_auth REQUIRED
http_access allow authenticated
http_access deny all

Dockerfile

FROM debian
RUN apt-get -y update && apt-get install -y curl supervisor git openssl  build-essential libssl-dev wget
RUN mkdir -p /var/log/supervisor
COPY supervisord.conf /etc/supervisor/conf.d/supervisord.conf
WORKDIR /apps/
RUN wget -O - http://www.squid-cache.org/Versions/v3/3.4/squid-3.4.14.tar.gz | tar zxfv -
RUN cd /apps/squid-3.4.14/ && ./configure --prefix=/apps/squid --enable-icap-client --enable-ssl --with-openssl --enable-ssl-crtd --enable-auth --enable-basic-auth-helpers="NCS
A" && make && make install
ADD . /apps/

RUN chown -R nobody /apps/
RUN mkdir -p  /apps/squid/var/lib/
RUN /apps/squid/libexec/ssl_crtd -c -s /apps/squid/var/lib/ssl_db -M 4MB
RUN chown -R nobody /apps/

EXPOSE 3128
#CMD ["/usr/bin/supervisord"]

Generating new CA

THis repo and image comes with a built-in CA. You are free to generate and volume mount your own CA.

To generate your CA, first grab an openssl.cnf file...eg create openssl.cnf in a folder ('myCA') from here:

https://gist.github.com/salrashid123/dbb032d4538c9df5d5ceed3f3e160ed4

then

mkdir myCA
cd myCA
mkdir new_certs
touch index.txt
echo 00 > serial

generate the CA:

openssl genrsa -out CA_key.pem 2048
openssl req -x509 -days 600 -new -nodes -key CA_key.pem -out CA_crt.pem -extensions v3_ca -config openssl.cnf    -subj "/C=US/ST=California/L=Mountain View/O=Google/OU=Enterprise/CN=MyCA"

note the -extension v3_ca i used and look for that in openssl.cnf

verify

openssl x509 -in CA_crt.pem -text -noout

        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:TRUE
            X509v3 Key Usage: 
                Digital Signature, Non Repudiation, Key Encipherment, Data Encipherment, Key Agreement, Certificate Sign, CRL Sign

the ssl_bump mode genrates server certs on the fly for you....but just to complete the steps, if you ever wanted to generate generate a server cert by hand:

openssl genrsa -out server.key 2048
openssl req -config openssl.cnf -days 400 -out server.csr -key server.key -new -sha256  -extensions v3_req  -subj "/C=US/ST=California/L=Mountain View/O=Google/OU=Enterprise/CN=squid.yourdomain.com"
openssl ca -config openssl.cnf -days 400 -notext  -in server.csr   -out server.crt

note the -extension v3_req i used and look for that in openssl.cnf