Dansguardian Web Content Filtering

Dansguardian web content filtering Skill level: Medium The instructions on this page require a basic knowledge of linux. Description Dansguardian is a web content filter, which analyses the actual content of web pages based on many criteria including phrase matching, PICS filtering, URL filtering and lists of banned sites. Each content type is given a score, and when the threshold score is exceeded, access to the web site is blocked. For additional information see http://dansguardian.org This HOWTO requires command line control to edit configuration files & restart the dansguardian service after configuration changes. There is a commercial implementation of Dansguardian for sme server which adds a server manager panel to allow GUI control of all Dansguardian functionality & settings, see http://dungog.net/wiki/Dungogdansguardian Information To have a proper understanding of how Dansguardian works and the importance of certain configuration settings you should read the detailed installation notes and Manual at the Dansguardian web site http://dansguardian.org An old version 2.4 installation notes are here: http://dansguardian.org/downloads/detailedinstallation2.4.html#further The FAQ is here: http://sourceforge.net/docman/display_doc.php?docid=27215&group_id=131757 Information about group configuration is here: http://contentfilter.futuragts.com/wiki/index.php? title=Group_Configuration Mailing list is here: http://tech.groups.yahoo.com/group/dansguardian/ The information on the Dansguardian website and other websites referred to, is of a generic nature and some of it is NOT applicable to sme server installations, refer to the instructions in this HOWTO in preference. Installation instructions Install dansguardian and it's dependencies from the smecontribs repository yum --enablerepo=smecontribs install smeserver-dansguardian Optional, download and install a set of blacklists from http://urlblacklist.com/ Note: It is not sufficient to simply install the package, the appropriate manual configuration is an integral part of getting Dansguardian working on your system. A minimal installation requires all the configuration steps listed below to be carried out, ie from the "Modifying Firewall and Proxy" section up to "Filter Groups and Auth login". Filter Group configuration is only required if you wish to control access on a per user basis. Tip: If you would like to have a graphical and web based overview of what dansguardian has analyzed then take a look at http://wiki.contribs.org/Dansguardian-stats Upgrading There are substantial changes between dansguardian v2.9 over previous v2.8 (or earlier) installations. The recommendation from dansguardian.org is to edit the new configuration files/lists rather than try to edit your old ones. Upgrading from 2.9 versions creates .rpmnew config files under /etc/dansguardian. This preserves your existing config files, but there is a chance that dansguardian won't start if parameters in the config file have changed.

Clamav libraries can cause problems when updating. If while updating you see something like Error: Missing Dependency: libclamav.so.3 is needed by package dansguardian Update with yum update --enablerepo=smecontribs dansguardian clamav then yum update Modifying Firewall and Proxy Configuring your system to force Dansguardian usage & prevent bypassing These instructions assume that the sme server is running in server gateway mode and acting as the gateway for your network, and the squid proxy is running on the same machine that Dansguardian is running on. If your server is configured in server only mode, then you will need to point your browser at that machine to find the squid proxy rather than the default gateway. Dansguardian uses port 8080 for web proxy requests. If your browser does not use port 8080 then Dansguardian filtering will be bypassed. To force this usage & prevent users bypassing filtering you should do ALL the following steps: 1) Configure your SME Server to use Transparent Proxy port 8080 and to block direct access to the squid proxy port 3128 & redirect port 80 to port 8080 Note the functionality to create the required custom firewall rules using iptables is built in to the smeserverdansguardian and is configured with the following commands. The Transparent proxy must also be enabled (which is the sme default) to prevent users bypassing Dansguardian filtering. config setprop squid TransparentPort 8080 config setprop squid Transparent yes config setprop dansguardian portblocking yes signal-event post-upgrade; signal-event reboot To return Transparent Proxy port to default value and to disable portblocking and to enable the Transparent proxy (which is the sme default) config setprop squid TransparentPort 3128 config setprop squid Transparent yes config delprop dansguardian portblocking signal-event post-upgrade; signal-event reboot Note: If you disable the Transparent Proxy feature of SME Server, Dansguardian can be bypassed at will by your users. You should keep the Transparent Proxy enabled (configured as above) for filtering to work. 2) Configure your workstation web browser to auto detect proxy port Go to your workstation and open your browser eg Internet Explorer or Firefox or your preferred browser Change the settings for Connections to LAN Select Auto detect proxy Or alternatively use the server IP 192.168.1.1 (or whatever yours is) and use a port of 8080 Bypass Proxy Allow individual PC's or selected sites to bypass the proxy (and dansguardian) entirely see Firewall#Bypass_Proxy.

Configuring Proxy to use Auth login Dansguardian supports different types of auth login ie ncsa, pam & ident, and allows control of web site access based on user name. For more details regarding the various auth login methods & other configuration requirements, see http://dansguardian.org or Google. Enable this functionality using the appropriate command, depending on your requirements. Most users of sme will probably use pam auth as that will authorise access against sme users and passwords. Choose one of the following config setprop squid RequireAuth pam config setprop squid RequireAuth ncsa config setprop squid RequireAuth ident To disable Auth login config delprop squid RequireAuth To enable any of the above setting changes you must follow the command with expand-template /etc/squid/squid.conf sv t /service/squid Using NCSA Auth login If you are using ncsa auth, create the user & password authentication list (you don't require users to be valid sme users) touch /etc/proxyusers Enter user names & password combinations one by one using this command htpasswd -b /etc/proxyusers username password You can test the authentication list using the following command /usr/lib/squid/ncsa_auth /etc/proxyusers Then enter the username & password when asked You will see a ERR or OK response Using Ident login If you are using ident auth, you will require a ident client on your workstation. One windows ident client is available from: https://sourceforge.net/projects/retinascan In some cases, the Windows firewall blocks access to the ident client and you will have to add an exception in your firewall rules as follows: Control Panel >> Windows Firewall >> Exceptions >> Add Port • • •

Name: auth Port number: 113 TCP

Modifying Dansguardian configuration You need to manually modify various configuration files. As a minimum the following basic changes need to be made: pico -w /etc/dansguardian/dansguardian.conf You will initially need to change:

accessdeniedaddress = 'http://YOURSERVER.YOURDOMAIN/cgibin/dansguardian.pl' for example to accessdeniedaddress = 'http://www.mydomain.com/cgi-bin/dansguardian.pl' Make any other required changes to suit your situation by carefully reviewing the other setting possibilities To save & exit Ctrl o Ctrl x

pico -w /etc/dansguardian/dansguardianf1.conf You may initially need to change (to suit adult level of protection) naughtynesslimit = 50 to naughtynesslimit = 160 (or even 250 or 300 depending on your sensitivity/tolerance requirements) Make any other required changes to suit your situation by carefully reviewing the other setting possibilities Save & exit Ctrl o Ctrl x

If you have additional filter groups, then additional configuration files will need to be created and modified. See section on "Filter Groups and Auth login" below.

Modifying other Dansguardian configuration files You will need to change other config files to suit your site requirements: You can read information in the beginning of each config file that explains usage & syntax These are located in /etc/dansguardian/lists... /etc/dansguardian/lists/f2/... & so on and subfolders eg pico -w /etc/dansguardian/lists/f2/bannedextensionlist make the required changes Ctrl o Ctrl x Most users will need to change these 4 files as a minimum bannedextensionlist bannedsitelist bannedurllist

exceptionsitelist You should review ALL the dansguardian config files in /etc/dansguardian/lists and subfolders as part of your initial Dansguardian setup. Some of the default settings in these files will prevent access to certain web sites and file types, which may conflict with your site requirements. See more details on the Dansguardian/ConfigFiles page of this Howto or at http://dansguardian.org Modifying the default html error message page You may also want to tailor the html template for the error message displayed when Dansguardian blocks a site, see /etc/dansguardian/languages/(languagename)/template.html eg pico -w /etc/dansguardian/languages/ukenglish/template.html Filter Groups and Auth login Dansguardian supports filter groups, which allow web access control of users based on filter group membership. Different users can have different access rights, and to achieve this each filter groups configuration files are configured with different access rights. Users are made members of the required filter group by editing /etc/dansguardian/lists/filtergroupslist When you open a web browser you get asked to login with a username & password. Depending on the users group membership they get filtered or unfiltered access. For additional information on filtering users access rights based on group membership (in conjunction with Auth login), see http:/dansguardian.org In order to use filter groups, you must be using one of the Auth login methods. If you wish to authenticate users when opening a browser using pam auth method, then you will need to disable Transparent Proxy as it is not compatible with this method. Issue the following command config setprop squid Transparent no expand-template /etc/squid/squid.conf sv t /service/squid Doing the above will also require you to manually specify the proxy settings in your browser, so you will need to add the server IP eg 192.168.1.1 and port 8080 for the proxy setting You cannot have pam auth enabled and Transparent Proxy set to yes. Issue one of the following commands to enable the type of Auth login required, which will then permit the configuration & use of Filter Groups config setprop squid RequireAuth pam config setprop squid RequireAuth ncsa config setprop squid RequireAuth ident To enable any of the above settings do expand-template /etc/squid/squid.conf sv t /service/squid

When using Filter Groups, a typical situation may have: Filter Group Filter Group Filter Group Filter Group rights) Filter Group

1 2 3 4

-

blocked users (no access) - See [1] standard users (standard access rights) guest users (limited access rights) power users (more generous access & file download

5 - admin users (unlimited access)

To create the additional filter group configuration files and folders do cp /etc/dansguardian/dansguardianf1.conf /etc/dansguardian/dansguardianf2.conf cp /etc/dansguardian/dansguardianf1.conf /etc/dansguardian/dansguardianf3.conf cp /etc/dansguardian/dansguardianf1.conf /etc/dansguardian/dansguardianf4.conf cp /etc/dansguardian/dansguardianf1.conf /etc/dansguardian/dansguardianf5.conf Because the Filter Group 1 (default) uses the configuration files located at the root of "/lists" directory, it is only necessary to create the rest of the directories f2, f3, f4 and f5 to host the configuration files for each Filter Group. Each filter directory (f2, f3, etc.) will house all the configuration files located at the root of "/lists" directory unless filtergroupslist, bannediplist and exceptioniplist, because they are not used for filtering because only they are called (logically) from the general configuration file dansguardian.conf. Because the configuration files are modified, is a smart idea to create a "virgin" copy of the files and then use it to create new filters directory. This directory will named "virgin" or something similar. mkdir -p /etc/dansguardian/lists/virgin cp /etc/dansguardian/lists/* /etc/dansguardian/lists/virgin rm -f /etc/dansguardian/lists/virgin/filtergroupslist rm -f /etc/dansguardian/lists/virgin/bannediplist rm -f /etc/dansguardian/lists/virgin/exceptioniplist cp -R /etc/dansguardian/lists/virgin /etc/dansguardian/lists/f2 cp -R /etc/dansguardian/lists/virgin /etc/dansguardian/lists/f3 cp -R /etc/dansguardian/lists/virgin /etc/dansguardian/lists/f4 cp -R /etc/dansguardian/lists/virgin /etc/dansguardian/lists/f5 (which will include all subfolders and files) Then edit & save the various main configuration files pico -w /etc/dansguardian/dansguardianf2.conf and change all instances of /lists/ to /lists/f2/ in filename locations

pico -w /etc/dansguardian/dansguardianf3.conf and change all instances of /lists/ to /lists/f3/ in filename locations

pico -w /etc/dansguardian/dansguardianf4.conf and change all instances of /lists/ to /lists/f4/ in filename locations

pico -w /etc/dansguardian/dansguardianf5.conf and change all instances of /lists/ to /lists/f5/ in filename locations

Edit & save the main dansguardian configuration file to setup filter groups pico -w /etc/dansguardian/dansguardian.conf Configure the following settings as shown #Filter group options filtergroups = 5 (or however many filter groups you want to have)

#Auth plugins authplugin = '/etc/dansguardian/authplugins/proxy-basic.conf' (leave other possibilities with # at start of line)

Edit Filter Group 1 main configuration file pico -w /etc/dansguardian/dansguardianf1.conf Configure the following settings as shown #Filter group mode groupmode = 0 #Filter group name groupname = 'Blocked Users'

Edit & save Filter Group 2 main configuration file pico -w /etc/dansguardian/dansguardianf2.conf Configure the following settings as shown #Filter group mode groupmode = 1 #Filter group name groupname = 'Standard Users'

Edit & save Filter Group 3 main configuration file pico -w /etc/dansguardian/dansguardianf3.conf Configure the following settings as shown #Filter group mode groupmode = 1 #Filter group name groupname = 'Guest Users'

Edit & save Filter Group 4 main configuration file pico -w /etc/dansguardian/dansguardianf4.conf Configure the following settings as shown #Filter group mode groupmode = 1 #Filter group name groupname = 'Power Users'

Edit & save Filter Group 5 main configuration file pico -w /etc/dansguardian/dansguardianf5.conf Configure the following settings as shown #Filter group mode groupmode = 2 #Filter group name groupname = 'Admin Users'

Edit & save the Filter Groups List file to add details of users and their group membership All users are automatically members of Filter Group 1, so you only need to add details of users who are in other groups. pico -w /etc/dansguardian/lists/filtergroupslist add entries for users who are members of other filter groups, use this format username=filtergroupnumber for example ray=filter2 george=filter3 mary=filter4 peter=filter5 and so on. Filter group 2,3,4 & 5 settings override filter group 1 settings. Restart dansguardian for changes to take effect /etc/init.d/dansguardian restart You can create as many groups as you want, using similar steps as above. Each group can have different levels of filtering eg different exceptionlists and naughtyness limits etc.

edit the exception and banned lists in pico -w /etc/dansguardian/lists/f2/exceptionsitelist etc etc and in each other group list structure eg f3, f4 & f5 Where f2 is a blocked group then setting changes to exception & other lists for that group will have no effect. Where f5 is a unfiltered group then setting changes to exception & other lists for that group will have no effect. ClamAV support If you want to use DansGuardian with SME antivirus, edit /etc/dansguardian/dansguardian.conf and uncomment following line: contentscanner = '/etc/dansguardian/contentscanners/clamdscan.conf' Now at the end of the file, add following lines: # OPTION: virusscanexceptions # If off, antivirus scanner will ignore exception sites and urls. virusscanexceptions = on also edit /etc/dansguardian/contentscanners/clamdscan.conf and uncomment + clamdudsfile = '/var/clamav/clamd.socket' - #clamdudsfile = '/var/run/clamav/clamd.socket' If you also want to be warned each time a bad page is blocked, edit /etc/dansguardian/dansguardianf1.conf and modify default settings: usesmtp = on mailfrom = 'dansguardian' avadmin = 'admin' contentadmin = 'admin' notifyav = on <= virus mail alert notifycontent = on <= content mail alert

Restart dansguardian and try to download eicar test virus DansGuardian should block the download! Other Dansguardian Config Files There are many other config files, including but not limited to the ones in this appendix

Dansguardian/ConfigFiles Starting Dansguardian After install & initial configuration you must manually start Dansguardian to enable web content filtering (Note that suitable links to start Dansguardian at startup/reboot are setup when the rpm is installed) /etc/init.d/dansguardian start Stopping Dansguardian If you need to stop Dansguardian (ie to disable filtering or test your system without Dansguardian running) /etc/init.d/dansguardian stop Restarting Dansguardian You will need to restart Dansguardian after making any configuration changes (so they can take effect) /etc/init.d/dansguardian restart Status check of Dansguardian If you need to check that Dansguardian is running /etc/init.d/dansguardian status

Testing access From a workstation web browser go to the site of www.sex.com or www.sex.com.au You should receive a message advising the site is blocked. Try browsing to other sites with inappropriate content or a site on your banned site list and you should receive a site blocked message. Remember that access to sites is controlled by settings in the config files.