File type-based filters

With File Filter, you can define undesired file types within the email filter profile and associate an action to be taken for each file type, such as block or log.

For each entry, you can also specify the protocol to inspect (SMTP, POP3, or IMAP) and if only encrypted files should be matched. While file filter entries are ordered, the block action takes precedence over the log action.

File filtering in email filter profiles is based only on the file type (file meta data) and not on file size or content. You would need to 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 in proxy mode policies. The traffic direction cannot be configured because it is implied by the protocol.

The following file types are supported:

File Type Name	Description
7z	Match 7-zip files
arj	Match arj compressed files
cab	Match Windows cab files
lzh	Match lzh compressed files
rar	Match rar archives
tar	Match tar files
zip	Match zip files
bzip	Match bzip files
gzip	Match gzip files
bzip2	Match bzip2 files
xz	Match xz files
bat	Match Windows batch files
msc	Match msc files
uue	Match uue files
mime	Match mime files
base64	Match base64 files
binhex	Match binhex files
bin	Match bin files
elf	Match elf files
exe	Match Windows executable files
hta	Match hta files
html	Match html files
jad	Match jad files
class	Match class files
cod	Match cod files
javascript	Match javascript files
msoffice	Match MS-Office files. For example, doc, xls, ppt, and so on.
msofficex	Match MS-Office XML files. For example, docx, xlsx, pptx, and so on.
fsg	Match fsg files
upx	Match upx files
petite	Match petite files
aspack	Match aspack files
prc	Match prc files
sis	Match sis files
hlp	Match Windows help files
activemime	Match activemime files
jpeg	Match jpeg files
gif	Match gif files
tiff	Match tiff files
png	Match png files
bmp	Match bmp files
unknown	Match unknown files
mpeg	Match mpeg files
mov	Match mov files
mp3	Match mp3 files
wma	Match wma files
wav	Match wav files
pdf	Match pdf files
avi	Match avi files
rm	Match rm files
torrent	Match torrent files
msi	Match Windows Installer msi bzip files
mach-o	Match Mach object files
dmg	Match Apple disk image files
.net	Match .NET files
xar	Match xar archive files
chm	Match Windows compiled HTML help files
iso	Match ISO archive files
crx	Match Chrome extension files

Example

In the following example, one file filter entry is created to block executable (exe) files from being sent or received, and a second entry logs any documents that are sent.

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

1. Configure an email filter profile:

   config emailfilter profile
       edit "file-type-filter"
           config file-filter 
               set status enable
               set log enable
               set scan-archive-contents enable
               config entries 
                   edit "filter1"
                       set comment "Block executable files"
                       set protocol smtp imap pop3
                       set action block
                       set encryption any
                       set file-type "exe"
                   next
                   edit "filter2"
                       set comment "Log document files"
                       set protocol smtp
                       set action log
                       set encryption any
                       set file-type "pdf" "msoffice" "msofficex"
                   next
               end
           end
           set spam-filtering enable
       next
   end

2. Use the profile in a firewall policy:

   config firewall policy
       edit 1
           set name "client-to-internet"
           set srcintf "port2"
           set dstintf "port1"
           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 emailfilter profile "file-type-filter"
           set profile-protocol-options "protocol"
           set ssl-ssh-profile "protocols"
           set nat enable
       next
   end

To view the file filter logs:

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

File filter block action:

1: date=2019-01-25 time=15:20:16 logid="0554020511" type="utm" subtype="file-filter" eventtype="file-filter" level="warning" vd="vdom1" eventtime=1548458416 policyid=1 sessionid=2881 srcip=10.1.100.12 srcport=45974 srcintf="port2" srcintfrole="undefined" dstip=172.16.200.56 dstport=143 dstintf="port1" dstintfrole="undefined" proto=6 service="IMAP" action="blocked" from="emailuser1@qa.fortinet.com" to="emailuser2@qa.fortinet.com" recipient="emailuser2" direction="incoming" subject="EXE file block" size="622346" attachment="yes" filename="putty.exe" filtername="filter1" filetype="exe"

File filter log action:

1: date=2020-06-25 time=10:56:04 logid="1900064000" type="utm" subtype="file-filter" eventtype="file-filter" level="warning" vd="root" eventtime=1593050164413818122 tz="+0900" policyid=1 sessionid=202 srcip=10.0.0.20 srcport=38984 srcintf="port1" srcintfrole="lan" dstip=10.0.10.20 dstport=110 dstintf="wan1" dstintfrole="wan" proto=6 service="POP3" profile="default" direction="incoming" action="blocked" from="guest@client.com" to="aki@fortitest.jp" recipient="aki@fortitest.jp" subject="Test mail" filtername="test" filename="test.pdf" filesize=24205 filetype="pdf" msg="File was blocked by file filter."

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

1. Go to Security Profiles > Email Filter.
2. Click Create New, or select an existing profile and click Edit.
3. Enable Enable Spam Detection and Filtering.
4. Enable File Filter.
5. Enable Log and Scan Archived Contents.
6. In the File Filter table, click Create New.

   

7. Configure the filters:
   1. filter1 blocks all sent or received executable files.

      

   2. filter2 logs all sent documents.

      

8. Click OK.
9. Add the new email filter profile to a firewall policy.
10. To see if there are file filter logs, go to VDOM > Log & Report > Forward Traffic. Select an entry and view the Log Details. The number of file filter logs for that entry is listed in the Other category.

    

    File filter logs can only be viewed in the CLI.