Warning: Please note that third-party browser add-ons or bots can alter the user-agent string on the client side itself. So the following may not work at all.

Syntax to block squid using User-Agent header

The acl syntax is as follows tn match on User-Agent header:

acl acl_name_here browser User_Agent_Here

Step 1: Edit squid.conf

Type the following command:

sudo vi /etc/squid/squid.conf

Step 2: Enable User-agent log in squid.conf

Make sure access_log set to combined (default is squid):

access_log daemon:/var/log/squid3/access.log combined

Step 3: Update/append acl

Local acl section and append the following configuration directives to your squid.conf file:

## block all version of MSIE ## 
acl block_browser browser MSIE
http_access deny block_browser

It is also possible to block specific version or other browsers too:

acl block_bad_browser browser MSIE.9
acl block_bad_browser browser MSIE.10
acl block_bad_browser browser Firefox
acl block_bad_browser browser Chrome/38
http_access deny block_bad_browser

You can also use the following syntax which is very fast:

acl aclname req_header header-name [-i] regex

Save and close the file.

Step 4: Reload squid server

To reload Squid Proxy Server without restarting squid daemon, enter:

sudo /usr/sbin/squid -k reconfigure

Step 5: Test it

Here is a sample screen showing blocked browser:

References

• Squid configuration directive acl documentation.