Squid

This guide explains how to configure Squid 6.x with the Glasswall Halo ICAP Server, enabling advanced threat protection through our advanced Content Disarm and Reconstruction (CDR) technology via Glasswall Halo.

Note: Instructions are based on Squid 6.x built with OpenSSL. For a full list of configuration options, please refer to the Squid Documentation.

Squid Integration Guide

Step 1: Basic configuration

Locate and edit your Squid configuration file, typically at:

/etc/squid/squid.conf
/etc/squid5/squid.conf

1A - Define access control lists

Uncomment or add the following ACLs for local networks and safe ports:

acl localnet src 10.0.0.0/8
acl localnet src 172.16.0.0/12
acl localnet src 192.168.0.0/16
acl localnet src fc00::/7
acl localnet src fe80::/10

acl SSL_ports port 443
acl Safe_ports port 80
acl Safe_ports port 21
acl Safe_ports port 443
acl Safe_ports port 70
acl Safe_ports port 210
acl Safe_ports port 1025-65535
acl Safe_ports port 280
acl Safe_ports port 488
acl Safe_ports port 591
acl Safe_ports port 777
acl CONNECT method CONNECT

1B - Allow local network access

Under Recommended minimum access permission configuration, add:

http_port 3128
http_access allow localnet
http_access allow localhost
http_access deny all

1C - Enable ICAP

Add the following to turn on ICAP support:

icap_enable on
icap_send_client_ip on
icap_preview_enable on
icap_preview_size 0
icap_service_failure_limit -1

1D - Configure request modification (uploads)

icap_service glasswall_req reqmod_precache bypass=0 icap://<Halo ICAP Server>:1344/req-cdr-service
adaptation_access glasswall_req allow all

1E - Configure response modification (downloads)

icap_service glasswall_resp respmod_precache bypass=0 icap://<Halo ICAP Server>:1344/req-cdr-service
adaptation_access glasswall_resp allow all

Step 2 - Persistent Connections

Squid 6.x supports persistent ICAP connections by default. To enforce:

icap_persistent_connections on

Tip: Ensure the ICAP server is also configured for persistent connections. Otherwise, disable them (off) to prevent errors.

Step 3 - Restart Squid

Apply changes:

sudo systemctl restart squid

Step 4 - Troubleshooting (Optional)

If you see errors like:

essential ICAP service is down after an options fetch failure: icap://<Halo ICAP Server>:1344/req-cdr-service [down,!opt]

Check the following:

Confirm you are running the latest stable Squid 6.x
If persistent connections cause issues, disable them:

icap_persistent_connections off

Step 5 - Scanning HTTPS Content

To scan encrypted HTTPS traffic, Squid must be compiled with SSL and configured for SSL bumping.

Requirements

Squid 6.x with OpenSSL
A root certificate for SSL interception

5A - Update listening port

http_port 3128 ssl-bump generate-host-certificates=on dynamic_cert_mem_cache_size=4MB cert=<SQUIDFOLDER>/etc/ssl/myc.pem

5B - Configure SSL bump

sslcrtd_program <SQUIDFOLDER>/lib/squid/ssl_crtd -s <SQUIDFOLDER>/var/cache/squid_ssldb -M 4MB
sslcrtd_children 5
ssl_bump server-first all

acl step1 at_step SslBump1
ssl_bump peek step1
ssl_bump bump all

sslproxy_cert_error deny all

5C - Generate and install root certificate

openssl req -new -newkey rsa:2048 -days 1000 -nodes -x509 -keyout myc.pem -out myc.pem

Initialize certificate storage:

rm -rf <SQUIDFOLDER>/var/cache/squid_ssldb
<SQUIDFOLDER>/lib/squid/ssl_crtd -c -s <SQUIDFOLDER>/var/cache/squid_ssldb

Important: Install myc.pem as a trusted root certificate in your browser.

Step 6 - Final Restart

Restart Squid to finalize all changes:

sudo systemctl restart squid