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.

Protocol	Proxy mode	Flow mode
CIFS	Yes	Yes
FTP	Yes	Yes
HTTP	Yes	Yes
IMAP	Yes	Yes
MAPI	Yes	No
POP3	Yes	Yes
SMTP	Yes	Yes
SSH	Yes	No

File filtering is based only on the file type (file meta data) and not on file size or content. A DLP sensor 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 filter types for more information).

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

GUI option	CLI option	Description
Basic profile settings
Name	name <string>	Enter a unique name for the profile.
Comments	comment <var-string>	Enter a comment (optional).
Scan archive contents	scan-archive-contents {enable | disable}	Enable to scan archive contents.
Feature set	feature-set {flow | proxy}	Select the feature set for the profile. The feature set mode must match the inspection mode used in the associated firewall policy. Flow-based Proxy-based
n/a	log {enable | disable}	Enable to use file filter logging. This setting is enabled by default.
n/a	extended-log {enable | disable}	Enable to use file filter extended logging. This setting is disabled by default.
n/a	replacemsg-group <string>	Set a replacement message group.
File filter rule settings
Name	name <string>	Enter a unique name for the rule.
Comments	comment <var-string>	Enter a comment (optional).
Protocols	protocol {option1}, {option2}, ...	Set the protocols to apply to the rule. By default, all protocols are configured: CIFS, FTP, HTTP, IMAP, POP3, and SMTP in flow mode. Additionally, MAPI and SSH are configured by default in proxy mode.
Traffic	direction {incoming | outgoing | any}	Set the traffic direction: Incoming/incoming: match files transmitted in the session's reply direction. Outgoing/outgoing: match files transmitted in the session's originating direction. Both/any: match files transmitted in the session's originating and reply directions.
Password-protected only	password-protected {yes | any}	Enable (yes) to match password-protected files. If the setting is not enabled, any file is matched.
File types	file-type <name1>, <name2>, ...	Select the file type. See Supported file types for the list of available options.
Action	action {log-only | block}	Set the action to take for a matched file: Monitor/log-only: allow the content and write a log message. Block/block: block the content and write a log message.

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" filtername="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" filtername="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" filtername="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" filtername="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" filtername="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" filtername="1" filename="index.html" filesize=21 filetype="html" msg="File was blocked by file filter."