Technical Tip: File Filter on WebFilter profile

[Somashekara_Hanumant]

Description
This article explains how to block file patterns on Webfilter profile for inbound/outbound traffic

Solution
File Filter allows the Web Filter profile to block files passing through a FortiGate based on file type.

HTTP and FTP File Filtering is configurable in Web Filter profile.

File Filtering in Web Filter profile is based on file type (file's meta data) only, and not on file size or file content.
Configure a DLP sensor to block files based on size or content such as SSN numbers, credit card numbers or regexp.

File filtering only works on proxy mode policies.

Configure the webfilter and enable the File Filter and select the file types are per the requirement and choose the correct protocol on which it is require to block, for which direction.

In the following example, three file filters are used in the Web Filter profile:
- Block PDFs from entering or leaving the network (filter1).
- Log the download of some graphics file-types via HTTP (filter2).
- Block EXE files from leaving to the network over FTP (filter3).

To configure a file-type based web filter in the CLI:

#config webfilter profile
    edit "webfilter-file-filter"
        config file-filter
            set status enable
            set log enable
            set scan-archive-contents enable
            config entries
                edit "filter1"
                    set comment "Block PDF files"
                    set protocol http ftp
                    set action block
                    set direction any
                    set encryption any
                    set file-type "pdf"
                next
                edit "filter2"
                    set comment "Log graphics files"
                    set protocol http
                    set action log
                    set direction incoming
                    set encryption any
                    set file-type "jpeg" "png" "gif"
                next
                edit "filter3"
                    set comment "Block upload of EXE files"
                    set protocol ftp
                    set action block
                    set direction outgoing
                    set encryption any
                    set file-type "exe"
                next
            end
        end
    next
end

After configuring file filters in Web Filter profile, apply it to a firewall policy using the following command:

#config firewall policy
    edit 1
        set name "client-to-internet"
        set srcintf "dmz"
        set dstintf "wan1"
        set srcaddr "all"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "ALL"
        set utm-status enable
        set utm-inspection-mode proxy
        set logtraffic all
        set webfilter profile "webfilter-filefilter"
        set profile-protocol-options "protocol"
        set ssl-ssh-profile "protocols"
        set nat enable
    next
end

To configure a file-type based web filter in the GUI:

1) Go to Security Profiles -> Web Filter
2) Click 'Create New' or select an existing profile and click 'Edit'.

3) Enable File Filter.
4) Enable Log and Scan Archived Contents.
5) In the File Filter table, click Create New.
6) Configure the filters:

filter1 blocks PDFs from entering or leaving the network.

filter2 logs the download of some graphics file-types via HTTP .

filter3 blocks EXE files from leaving to the network over FTP .

Click OK.
Add the new web filter profile to a firewall policy.

Log examples

File filter block action:

1: date=2019-03-19 time=09:42:15 logid="0346012673" type="utm" subtype="webfilter" eventtype="file_filter" level="warning" vd="vd1" eventtime=1548438135 policyid=1 sessionid=29449 srcip=10.1.100.22 srcport=52816 srcintf="dmz" srcintfrole="undefined" dstip=172.16.200.55 dstport=80 dstintf="wan1" dstintfrole="undefined" proto=6 service="HTTP" hostname="172.16.200.55" profile="webfilter-filefilter" action="blocked" reqtype="direct" url="/app_data/test1.pdf" sentbyte=0 rcvdbyte=0 direction="incoming" filename="test1.pdf" filtername="filter1" filetype="pdf" msg="File was blocked by file filter."
File filter log action:
2: date=2019-03-19 time=10:48:23 logid="0346012672" type="utm" subtype="webfilter" eventtype="file_filter" level="notice" vd="vd1" eventtime=1548442102 policyid=1 sessionid=521 srcip=10.1.100.22 srcport=52894 srcintf="dmz" srcintfrole="undefined" dstip=172.16.200.55 dstport=80 dstintf="wan1" dstintfrole="undefined" proto=6 service="HTTP" hostname="172.16.200.55" profile="webfilter-filefilter" action="passthrough" reqtype="direct" url="/app_data/park.jpg" sentbyte=0 rcvdbyte=0 direction="incoming" filename="park.jpg" filtername="filter2" filetype="jpeg" msg="File was detected by file filter."

In the GUI:
Go to VDOM -> Log & Report -> Web Filter