File filter

A file filter can be configured to control the flow of different types of files passing through FortiGate. This is done by setting up rules that specify which file types are allowed or blocked. The file filter can be applied directly to firewall policies and supports various traffic protocols in proxy or flow mode. The feature set setting (proxy or flow) in the file filter profile must match the inspection mode setting (proxy or flow) in the associated firewall policy. For example, a flow-based file filter profile must be used with a flow-based firewall policy.

Prior to FortiOS 6.4.1, file filter was embedded in the web filter, email filter, SSH inspection, and CIFS profiles.

File filtering is based only on the file type (file meta data) and not on file size or content. A DLP dictionary, sensor, and profile would need to be configured to block files based on size or content, such as SSN numbers, credit card numbers, or regular expressions (see Basic DLP settings for more information).

The following options can be configured in a file filter profile:

config system settings
    set gui-proxy-inspection enable
end

Configuring a file filter profile

In this example, a flow-based file filter is created that has two rules.

• Rule 1: applied to HTTP, FTP, SMTP, IMAP, POP3, and CIFS to monitor any matched .NET, 7-Zip, ActiveMime, ARJ, ASPack, AVI, Base64, Windows batch, BinHex, BMP, Bzip, and Bzip2 files transmitted in the session's originating and reply directions.
• Rule 2: applied to HTTP, FTP, SMTP, IMAP, POP3, and CIFS to block any matched SIS, TAR. TIFF, torrent, UPX, UUE, WAV, WMA. ZAR archive, XZ, and ZIP files transmitted in the session's originating direction.

To configure a file filter in the GUI:

1. Configure the filter profile:

   1. Go to Security Profiles > File Filter and click Create New.

   2. Enter a name.

   3. Set the Feature set to Flow-based.

   4. In the Rules table, click Create New.

   5. Configure rule 1 as follows:

      Name	r1
      Protocols	HTTP, FTP, SMTP, IMAP, POP3, CIFS
      Traffic	Both
      Password-protected only	Deselect
      File types	.net, 7z, activemime, arj, aspack, avi, base64, bat, binhex, bmp, bzip, bzip2
      Action	Monitor

   6. Click OK to save the rule.

   7. In the Rules table, click Create New and configure rule 2 as follows:

      Name	r2
      Protocols	HTTP, FTP, SMTP, IMAP, POP3, CIFS
      Traffic	Outgoing
      Password-protected only	Deselect
      File types	sis, tar, tiff, torrent, upx, uue, wav, wma, xar, xz, zip
      Action	Block

      

   8. Click OK to save the rule.

   9. Click OK to save the filter profile.

      

2. Apply the filter to a policy:
   1. Go to Policy & Objects > Firewall Policy and edit an existing policy or create a new one.
   2. In the Security Profiles section, enable File Filter.
   3. Select the filter from the dropdown box (test).
   4. Configure the other settings as needed.
   5. Click OK.

To configure a file filter in the CLI:

1. Configure the file filter profile:

   config file-filter profile
       edit "test"
           set comment ''
           set feature-set flow
           set replacemsg-group ''
           set log enable
           set scan-archive-contents enable
           config rules
               edit "r1"
                   set comment ''
                   set protocol http ftp smtp imap pop3 cifs
                   set action log-only
                   set direction any
                   set password-protected any
                   set file-type ".net" "7z" "activemime" "arj" "aspack" "avi" "base64" "bat" "binhex" "bmp" "bzip" "bzip2"
               next
               edit "r2"
                   set comment ''
                   set protocol http ftp smtp imap pop3 cifs
                   set action block
                   set direction outgoing
                   set password-protected any
                   set file-type "sis" "tar" "tiff" "torrent" "upx" "uue" "wav" "wma" "xar" "xz" "zip"
               next
           end
       next
   end

2. Apply the filter to a policy:

   config firewall policy
       edit 1
           set name "filefilter-policy"
           set srcintf "port10"
           set dstintf "port9"
           set srcaddr "all"
           set dstaddr "all"
           set srcaddr6 "all"
           set dstaddr6 "all"
           set action accept
           set schedule "always"
           set service "ALL"
           set utm-status enable
           set profile-protocol-options "protocol"
           set ssl-ssh-profile "protocols"
           set file-filter-profile "test"
           set auto-asic-offload disable
           set np-acceleration disable
           set nat enable
       next
   end

To view file filter logs in the GUI:

1. Go to Log & Report > Security Events.
2. Select the File Filter card.

To view file filter logs in the CLI:

# execute log filter category utm-file-filter			
# execute log display

Log samples

date=2020-04-21 time=17:04:02 logid="1900064000" type="utm" subtype="file-filter" eventtype="file-filter" level="warning" vd="root" eventtime=1587513843211612684 tz="-0700" policyid=1 sessionid=1751 srcip=10.1.100.22 srcport=57382 srcintf="port21" srcintfrole="undefined" dstip=172.16.200.44 dstport=445 dstintf="port23" dstintfrole="undefined" proto=6 service="CIFS" profile="filefilter" direction="incoming" action="blocked" rulename="1" filename="sample\\putty.exe" filesize=454656 filetype="exe" msg="File was blocked by file filter."

date=2020-04-21 time=17:03:54 logid="1900064000" type="utm" subtype="file-filter" eventtype="file-filter" level="warning" vd="root" eventtime=1587513834376811325 tz="-0700" policyid=1 sessionid=1742 srcip=10.1.100.22 srcport=36754 srcintf="port21" srcintfrole="undefined" dstip=172.16.200.44 dstport=22 dstintf="port23" dstintfrole="undefined" proto=6 service="SSH" subservice="SCP" profile="filefilter" direction="incoming" action="blocked" rulename="1" filename="test.pdf" filesize=571051 filetype="pdf" msg="File was blocked by file filter."

date=2020-04-21 time=17:00:30 logid="1900064000" type="utm" subtype="file-filter" eventtype="file-filter" level="warning" vd="root" eventtime=1587513630482716465 tz="-0700" policyid=1 sessionid=1684 srcip=10.1.100.22 srcport=58524 srcintf="port21" srcintfrole="undefined" dstip=172.16.200.44 dstport=143 dstintf="port23" dstintfrole="undefined" proto=6 service="IMAP" profile="filefilter" direction="incoming" action="blocked" from="pc4user1@qa.fortinet.com" to="pc4user2@qa.fortinet.com" recipient="pc4user2" subject="QA Test" rulename="1" filename="test.JPG" filesize=48079 filetype="jpeg" msg="File was blocked by file filter."

date=2020-04-21 time=16:59:58 logid="1900064000" type="utm" subtype="file-filter" eventtype="file-filter" level="warning" vd="root" eventtime=1587513598866551739 tz="-0700" policyid=1 sessionid=1674 srcip=10.1.100.22 srcport=39854 srcintf="port21" srcintfrole="undefined" dstip=172.16.200.44 dstport=110 dstintf="port23" dstintfrole="undefined" proto=6 service="POP3" profile="filefilter" direction="incoming" action="blocked" from="pc4user1@qa.fortinet.com" to="pc4user2@qa.fortinet.com" recipient="pc4user2" subject="QA Test" rulename="1" filename="test.JPG" filesize=48079 filetype="jpeg" msg="File was blocked by file filter."

date=2020-04-21 time=16:58:31 logid="1900064000" type="utm" subtype="file-filter" eventtype="file-filter" level="warning" vd="root" eventtime=1587513511516745955 tz="-0700" policyid=1 sessionid=1619 srcip=10.1.100.22 srcport=53144 srcintf="port21" srcintfrole="undefined" dstip=172.16.200.44 dstport=25 dstintf="port23" dstintfrole="undefined" proto=6 service="SMTP" profile="filefilter" direction="outgoing" action="blocked" from="pc4user1@qa.fortinet.com" to="pc4user2@qa.fortinet.com" sender="pc4user1@qa.fortinet.com" recipient="pc4user2@qa.fortinet.com" subject="QA Test" rulename="1" filename="test.PNG" filesize=65173 filetype="png" msg="File was blocked by file filter."

date=2020-04-21 time=16:58:14 logid="1900064000" type="utm" subtype="file-filter" eventtype="file-filter" level="warning" vd="root" eventtime=1587513494608988795 tz="-0700" policyid=1 sessionid=1605 srcip=10.1.100.22 srcport=43186 srcintf="port21" srcintfrole="undefined" dstip=172.16.200.44 dstport=21 dstintf="port23" dstintfrole="undefined" proto=6 service="FTP" profile="filefilter" direction="incoming" action="blocked" rulename="1" filename="index.html" filesize=21 filetype="html" msg="File was blocked by file filter."