SquidClamAv is a dedicated ClamAV antivirus redirector for Squid. It can run antivirus checks based on filename regex, content-type regex, and more. It is easy to install and works even with heavy Squid access.
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README

NAME
    SquidClamav v6 - HTTP Antivirus for Squid based on ClamAv and the ICAP
    protocol

DESCRIPTION
    SquidClamav v6 is an antivirus for the Squid proxy based on the ICAP
    protocol and the awards-winning ClamAv anti-virus toolkit. Using it will
    help you securing your home or enterprise network web traffic.
    SquidClamav is the most efficient antivirus tool for HTTP traffic
    available for free, it is written in C as a c-icap service and can
    handle several thousands of connections at once.

    SquidClamav v6 only scan the HTTP stream sent by Squid through the ICAP
    server. It doesn't make HTTP requests itself so this is a gain of
    performance and ensures that the data scanned is the same as the user
    has requested.

    Why use c-icap server? This is the only open source icap server written
    in C, it is very fast and stable.

    Why writing another clamav c-icap module? Well, to be honest, outside
    the survival of SquidClamav, I think that using clamd instead of
    libclamav to scan files is speediest and more simple than the srv_clamav
    module provided with the c-icap server.

    SquidClamav v6 is faster than any other HTTP antivirus and can handle
    several thousands of simultaneous users at once, this is what we need.

    The other unique feature of SquidClamav is that you can have Clamd
    failover by setting up up to 4 clamd server IP addresses. When a clamd
    server is not reachable in one second, SquidClamav switches to the next
    IP address.

    If you are using ClamAV above 0.95, SquidClamav will have support for
    Google Safe Browsing database. All signatures provided by Google Safe
    Browsing Database will be prefixed with the Safebrowsing tag. If ClamAV
    reports:

            Safebrowsing.<something> FOUND

    This will be redirected by squidclamav just like if a virus was found.

USAGE
  Generic Program Information
    SquidClamav v6 has been completely rewritten to be used through the
    Squid v3.x ICAP feature allowing "on stream" scanning. It is now built
    as a c-icap server service but keeps all features from v5 and is fully
    compatible with the old SquidClamav configuration file. The squidclamav
    configuration file is unchanged minus some obsolete directives.

    This also means that SquidClamav can no more be run into an interactive
    console for testing your URL. All debug information will now go to the
    c-icap logfile.

  Installing Squid
  Setting SquidClamav as Squid Icap service
    I want SquidClamav to be installed as a c-icap service, to be configured
    as easy as possible and to be compatible with the old configuration
    file. This means that I voluntary omit some capabilities of c-icap
    server to preserve a full compatibility with the old squidclamav.conf
    file.

   Squid v3.x installation and configuration
    To have full and stable icap support with Squid you must use the 3.x
    branch and configure squid with the following option:

            --enable-icap-client

    I don't know what other options you are using but you have to add this
    one to your configure command. If you prefer to use distribution
    packaging you may already have it configured like this if you can
    install the c-icap package too.

    If you don't know, run the following command an search for the
    configuration directive: --enable-icap-client

            /usr/local/squid/sbin/squid -v | grep "enable-icap-client"

    If it is not enable you must reinstall Squid with this configuration
    option or install the additional packages.

    Once you have it enabled, to integrate c-icap and SquidClamav to your
    squid cache just edit squid.conf and set the following directives.

    Squid 3.4.x configuration
        There are some configuration differences between 3.1.x and 3.4.x
        Squid version. Here are the directives I use for Squid 3.4.x:

                icap_enable on
                icap_send_client_ip on
                icap_send_client_username on
                icap_client_username_encode off
                icap_client_username_header X-Authenticated-User
                icap_preview_enable on
                icap_preview_size 1024
                icap_service service_avi_req reqmod_precache
                icap://localhost:1344/squidclamav bypass=off
                adaptation_access service_avi_req allow all
                icap_service service_avi_resp respmod_precache
                icap://localhost:1344/squidclamav bypass=on
                adaptation_access service_avi_resp allow all

        If you don't know where to put them in squid.conf, just search for
        'icap_.*' and add those configuration lines at the end of the icap
        section.

    Squid 3.1.x configuration
        There are some configuration differences between 3.1.x and 3.0.x
        Squid version. Here are the directives I use for Squid 3.1.x:

                icap_enable on
                icap_send_client_ip on
                icap_send_client_username on
                icap_client_username_encode off
                icap_client_username_header X-Authenticated-User
                icap_preview_enable on
                icap_preview_size 1024
                icap_service service_req reqmod_precache bypass=1 icap://127.0.0.1:1344/squidclamav
                adaptation_access service_req allow all
                icap_service service_resp respmod_precache bypass=1 icap://127.0.0.1:1344/squidclamav
                adaptation_access service_resp allow all

        If you don't know where to put them in squid.conf, just search for
        'icap_.*' and add those configuration lines at the end of the icap
        section.

        Here the bypass is set to 1, that means that in case of squidclamav
        problems squid will simply ignore the error and continue. This is
        the equivalent of the bridge mode in version 5.x of suidclamav.

    Squid 3.0.x configuration
        For squid 3.0.x you must replace 'bypass=1' by '1' or 'bypass=0' by
        '0' and the access to the service is defined at a class level. Only
        the last four configuration lines change from version 3.1.x.

                icap_enable on
                icap_send_client_ip on
                icap_send_client_username on
                icap_client_username_encode off
                icap_client_username_header X-Authenticated-User
                icap_preview_enable on
                icap_preview_size 1024
                icap_service service_req reqmod_precache 1 icap://127.0.0.1:1344/squidclamav
                icap_service service_resp respmod_precache 1 icap://127.0.0.1:1344/squidclamav
                icap_class class_avreq service_req
                icap_class class_avresp service_resp
                icap_access class_avreq allow all
                icap_access class_avresp allow all

        If you don't know where to put them in squid.conf, just search for
        'icap_.*' and add those configuration lines at the end of the icap
        section.

        Here the bypass is set to 1, that means that in case of squidclamav
        problems squid will simply ignore the error and continue. This is
        the equivalent of the bridge mode in version 5.x of suidclamav.

    What do that configuration directives do? They enable Squid's ICAP
    client and tell Squid to send the logged username and client's IP
    address to the ICAP server. They also enable preview for faster
    SquidClamav work. The last four lines define how to call the ICAP
    server. Here we call the squidclamav service on localhost and port 1344
    (host and port can be changed). The bypass parameter set to 1 means that
    Squid will continue without bothering about ICAP server or SquidClamav
    failure. This is just like the old bridge mode in previous releases of
    SquidClamAV. I don't want users to be bored by a continuously error
    message if SquidClamav or c-icap produce errors or if there's an error
    in the configuration file. Users don't have to know about that, they
    want to surf and don't care about your problems :-) If you don't think
    like me, just set the bypass argument to 0 and Squid will return an
    error message in case of a failure.

   C-icap server installation/configuration
    If you don't have package solutions or encounter problems when
    installing SquidClamav I recommand you to install the c-icap server from
    source as following. You can download it from SourceForge at
    http://c-icap.sourceforge.net/. Choose version c-icap-0.3.2 or later
    versions, then run:

            ./configure --prefix=/usr/local/c-icap --enable-large-files
            make
            make install

    Then, edit the file /usr/local/c-icap/etc/c-icap.conf. It contains a set
    of documented values that configure the c-icap server. To enable the
    support of SquidClamav just add the following line to the end of the
    file:

            Service squidclamav squidclamav.so

    Don't care about the srv_clamav.* configuration directives, this will
    not break anything. SquidClamav doesn't use them but reads its own
    directives from the file /etc/squidclamav.conf.

    You can disable the c-icap embedded modules by commenting out these
    lines:

            #Service url_check_module srv_url_check.so
            #Service antivirus_module srv_clamav.so

    This will preserve some resources.

    Following your installation you may need to create the /var/run/c-icap/
    where c-icap server is writing pid and socket file.

    You may also want to change the user/group owning c-icap's processes. By
    default the owner is the user/group who runs the program. I recommand
    you to change them to the same user/group running your Squid cache. For
    example:

            User proxy
            Group proxy

    Of course you will need to change the owner of directory
    /var/run/c-icap/ and the directory of your server log. See the ServerLog
    directive to get the path. For me, I use the following commands to set
    the good rights on my installation:

            mkdir /var/run/c-icap/
            chown -R proxy:proxy /var/run/c-icap/
            chown -R proxy:proxy /usr/local/c-icap/

    After that you can run the c-icap server as explained below.

   SquidClamav installation/configuration
    Installing SquidClamav requires that you already have installed the
    c-icap as explained above. You must provide the installation path of
    c-icap to the configure command as following:

            ./configure
            make
            make install

    This will install the squidclamav.so library into the c-icap
    modules/services repository.

    Note that if the c-icap installation does not save the c-icap-config
    program in a directory that can be found in your default path you will
    need to give the path to this program to squidclamav at configure time:

            ./configure --with-c-icap=/usr/local/c-icap/
            make && make install

   Running c-icap server
    Finally, you can run the c-icap server as root user:

            /usr/local/c-icap/bin/c-icap

    or any other path to the binary. If you want to display debugging
    information on the terminal, the previous command should be executed
    with the following arguments:

            /usr/local/c-icap/bin/c-icap -N -D -d 10

    The first argument -N prevents the c-icap server from forking into the
    background, the second argument -D enables the printing of messages to
    standard output, and the third argument -d 10 enables the printing of
    full debugging information.

   Reloading configuration without restarting the c-icap server
    To force SquidClamav to reread its configuration file after changes you
    can send the following command to the c-icap server

            echo -n "squidclamav:cfgreload" > /var/run/c-icap/c-icap.ctl

    It will reread all its configuration directives and restart pipes to
    squidGuard. So if you make changes to squidGuard you must execute this
    command to activate them in SquidClamav.

    Or to be sure that everything is really initialized or that you have
    made change to the c-icap configuration file you can run the following
    command:

            echo -n "reconfigure" > /var/run/c-icap/c-icap.ctl

    The service will reread the config file without the need for stopping
    and restarting the c-icap server. The service will just be
    reinitialized.

CONFIGURATION
    By default, the configuration file must be /etc/squidclamav.conf, you
    may not use an other path unless you change it in the source code (see
    src/squidclamav.h).

    SquidClamav installation will create a default file with the maximum
    security level. If you have low resources on your server there's some
    predefined pattern optimized for speed. Feel free to modify it to match
    your desired security level.

    The format of the configuration file consists in always lower case
    configuration directive names followed by a value. The name and the
    value must be separated by a single space character. Comments are lines
    starting with a '#' character.

  Global configuration
   Log file and debug
    In version 6.x the directives 'logfile', 'debug' and 'stat' are obsolete
    as logging and debug are now handled by the c-icap server. You can
    control them using the following c-icap.conf directives:

            ServerLog /usr/local/c-icap/var/log/server.log
            DebugLevel 0

    Debug information is disable by default, do not enable it on production
    systems as it costs a lot of performance. The debug level can be set
    from 1 up to 3 for SquidClamav but can be up to 10 for c-icap.

   Clamd daemon
    SquidClamav needs to know where to contact clamd, the ClamAV daemon, for
    on stream virus scanning.

            clamd_local /tmp/clamd
            #clamd_ip 192.168.1.5
            #clamd_port 3310

    By default SquidClamav will contact clamd locally on the /tmp/clamd unix
    socket (clamd_local). If your clamd daemon uses INET socket or stays in
    a remote server, you have to set the IP address and the port with
    clamd_ip and clamd_port.

    If you use INET socket the 'clamd_local' directive must be commented, or
    SquidClamav will always use the clamd_local directive.

   Clamd failover
    If you have multiple ClamAv servers, SquidClamav is able to do failover
    between them. You just have to set 'clamd_ip' to a list of IP adresses
    separated by a comma. Do not insert space characters in this list or it
    will break all. For example:

            clamd_ip 192.168.1.5,192.168.1.13,192.168.1.9
            clamd_port 3310
            timeout 1

    You can set up to 5 clamd servers. The clamd port must be the same for
    all these servers as 'clamd_port' only accepts one single value.

    SquidClamav will always connect to the first IP address available. If
    this fails it will try the next defined IP address after 1 second. When
    a connect can be established SquidClamav will reuse this last "working"
    IP address first to not slow down process the next time.

    If you think 1 second is a low value, you can change the connect timeout
    by editing file squidclamav.conf and set the 'timeout' directive to a
    higher value. For example :

            timeout 2

    Value must be set in seconds. Do not set it too high (< 5) or you can
    slow down everything.

   Redirection
   URL redirect
    When a virus is detected SquidClamav needs to redirect the client to a
    warning page. The SquidClamav distribution contains a set of Perl CGI
    scripts with different languages that you can use. To specify this
    redirection you have to have to specify a redirect URL to the 'redirect'
    directive as follow:

            redirect http://proxy.samse.fr/cgi-bin/clwarn.cgi

    Take a look in the cgi-bin directory to see all translations of this cgi
    script.

    Squidclamav will pass the following parameters to this CGI:

            url=ORIGNAL_HTTP_REQUEST
            virus=NAME_OF_THE_VIRUS
            source=DOWNLOADER_IP_ADDRESS
            user=DOWNLOADER_IDENT

    If this directive is disabled squidclamav will use c-icap error
    templates to report issues. See below.

   Using c-icap template instead of redirect scripts
    If the redirect directive is not set, SquidClamav will attempt to load a
    template up from disk and send this back to the user. By default this
    template is found at the following path:

            /usr/share/c_icap/templates/squidclamav/en/MALWARE_FOUND

    Available format tokens are all of those available to the LogFormat
    directive of c-icap, plus an additional token:

            %mn - formatted name of the malware, as given by ClamAV.

   Notice redirection into log file
    To log every redirection enable the 'logredir' configuration directive:

            logredir 1

    By default it is disabled as you can also log this information with the
    cgi-script or send an email.

   Chained Url Checker
    The squidguard directive is preserved for backward compatibility but you
    must remove it from your configuration file as it could result in many
    squidclamav crashes.

    Please use the 'url_rewrite_program' squid.conf directive instead to
    call squidGuard.

            url_rewrite_program /usr/bin/squidGuard
            url_rewrite_children 15
            url_rewrite_access allow all

    If you still want to use it, SquidClamav allows you to chain the
    SquidGuard program to check the URL requested against blocklists using
    the 'squidguard' directive. You just have to give the path to the
    program.

            squidguard /usr/local/squidGuard/bin/squidGuard

    The chained program is called before the virus scan and any other
    SquidClamav operations. The call to this program can be disabled with
    the 'whitelist', 'trustuser' and 'trustclient' directives. See
    SquidClamav Patterns for more information.

    To log every chained program redirection enable the 'logredir'
    configuration directive as following:

            logredir 1

    By default it is disabled as you can also log this information with
    squidguard.

   Maxsize
    This directive allows to disable virus scan completely for files bigger
    than the value in bytes. Default is 0, no size limit as you may want to
    control download size into squid.conf or clamd.

            maxsize 2000000

    If you want to abort virus scan after a certain amount of data you must
    take a look at the clamd configuration directive 'StreamMaxLength' that
    will close a stream when the given size is reached.

  Controlling SquidClamav behaviour
    As in SquidClamav v5.x, v6.0 will scan all downloaded files by default.
    You have five directives to control the way things must work.

    All these directives used extended regex pattern matching and are case
    insensitive.

   Control both chained program and virus scan
    There are 3 configuration directives that allow you to disable virus
    scan and call to chained redirector like SquidGuard. Those pattern
    matchings are searched as soon as a Squid entry is received.

    whitelist
        The 'whitelist' configuration directive allows you to disable
        chained program and virus scan at URL level. When the given pattern
        matches the URL, SquidClamav falls back to Squid instantly.

        For example:

                whitelist \.clamav\.net

        will deliver any files from hosts on clamav.net domain directly.

    trustuser
        The 'trustuser' directive allows you to disable chained program and
        virus scan when an ident matches the search pattern. On regex found
        SquidClamav falls back to Squid instantly. Of course you must have
        Squid authentication helper enabled.

        For example:

                trustuser administrator

        will let user logged as administrator to not be bored by chained
        program and virus scan.

    trustclient
        The 'trustclient' directive allows you to disable chained program
        and virus scan if the client source IP address or DNS name match the
        search pattern. The source IP address can be a single IP address or
        an address range following the given regex pattern.

        For example:

                trustclient ^192\.168\.1\.1$
                trustclient ^192\.168\.1\..*$
                trustclient ^mypc\.domain\.dom$

        The first and the last entry will disable chained program and virus
        scan for a single computer and the second will do for en entire
        class C network.

    dnslookup
        Enable / disable DNS lookup of client IP address. Default is enabled
        '1' to preserve backward compatibility but you must deactivate this
        feature if you don't use trustclient with hostname in the regexp or
        if you don't have a DNS on your network. Disabling it will also
        speed up squidclamav.

   Safebrowsing
    ClamAV 0.95 introduced support for Google Safe Browsing database. The
    database is packed inside a CVD file and distributed through our mirror
    network as safebrowsing.cvd. This feature is disabled by default on all
    clamav installations.

    In order to enable this feature, you must first add “SafeBrowsing
    Yes” to freshclam.conf. There is no option in clamd.conf. If the
    engine finds Google Safe Browsing files in the database directory,
    ClamAV will enable safe browsing. To turn it off you need to update
    freshclam.conf and remove the safebrowsing files from the database
    directory before restarting clamd.

    Then to enable this feature into SquidClamav you have to enable the
    following configuration directive.

    safebrowsing
        Enable / Disable Clamav Safe Browsing feature. You mus have enabled
        the corresponding behavior in clamd by enabling SafeBrowsing into
        freshclam.conf Enabling it will first make a safe browsing request
        to clamd and then the virus scan request.

   Control virus scan
    There are 3 configuration directives that allow you to disable virus
    scan for downloaded files.

    abort
        The 'abort' directive will let you disable virus scanning at URL
        level (not chained program). When the URL matches the regex pattern,
        SquidClamav falls back to Squid immediately after the call to the
        chained program, if one is defined there.

        For example:

                abort \.squid-cache\.org
                abort .*\.(png|gif|jpg)$

        The first regexp will exclude any file hosted on domain
        squid-cache.org from virus scanning, the last one will exclude all
        PNG, GIF and JPEG image from scanning.

    abortcontent
        The 'abortcontent' directive allows you to exclude any file from
        virus scanning, whose Content-Type matches the regex pattern. This
        directive costs more time because SquidClamav needs to download the
        HTTP header for a file with a HEAD request. Note that some sites do
        not answer to HEAD requests so the content type will not be able to
        be retrieved so they will be scanned.

        Example:

                abortcontent ^image\/.*$
                abortcontent ^video\/x-flv$

        The first directive will complete the "abort .*\.(png|gif|jpg)$"
        previous directive to match dynamic image or with parameters at end.
        The second will allow your users to view streamed video instantly.

    maxsize
        As said above, the 'maxsize' directive allows you not to scan a file
        when the content-length of the file is bigger than the defined
        value. By default there's no size limit.

  Testing SquidClamav
    As SquidClamav v6.0 is now a c-icap service, it can no more be run at
    console in interactive mode. To check what is going wrong, you must edit
    c-icap.conf file, set DebugLevel to 3 and enable ServerLog. Then check
    for lines with squidclamav string in the log file which is defined with
    ServerLog in squidclamav's config.

  Performance
    With SquidClamav v6.x the way to tune your service is to tune c-icap
    server and clamd daemon. On heavy http access, putting the clamd daemon
    on a dedicated server with multiple CPU will really help.

    If you experience Squid "ICAP protocol error" (with bypass enabled)
    please consider increasing the following c-icp parameters: StartServers,
    MaxServers, MinSpareThreads, MaxSpareThreads, ThreadsPerChild.
    Increasing MaxThreads parameter in clamd.conf may also help.

BUGS
    Please report any bugs, patches, discussion, etc. to <gilles AT darold
    DOT net>.

FEATURE REQUESTS
    If you need new features let me know at <gilles AT darold DOT net>. This
    helps a lot to develop a better/useful tool.

HOW TO CONTRIBUTE ?
    Any contribution to build a better tool is welcome, you just have to
    send me your ideas, features requests or patches and they will be
    applied.

AUTHOR
    Gilles Darold <gilles AT darold DOT net>

ACKNOWLEDGEMENT
    Thanks to Squid-cache.org, Clamav.net and c-icap.sf.net for their great
    software.

    Special thanks to Christos Tsantilas for his implementation of the
    c-icap server. Lots of SquidClamav v6 source code has been learned or
    simply cut and pasted from the source code of his clamav service.

    I must also thank all the great contributors:

            - Leonardo Humberto Liporati from www.ig.com.br
            - Dale Laushman from The Uptime Group
            - Rainer schoepf from Proteosys.com
            - Yann Ormanns

    and all others who help me to build a useful and reliable product.

LICENSE
    Copyright (c) 2005-2016 Gilles Darold - All rights reserved.

    Some code is Copyright (C) 2004-2008 Christos Tsantilas

    This program is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by the
    Free Software Foundation, either version 3 of the License, or any later
    version.

    This program is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
    Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program. If not, see < http://www.gnu.org/licenses/ >.