File
Blocking Profiles allow you to identify specific file types
that you want to want to block or monitor. For most traffic (including
traffic on your internal network), block files that are known to
carry threats or that have no real use case for upload/download.
Currently, these include batch files, DLLs, Java class files, help
files, Windows shortcuts (.lnk), and BitTorrent files. Additionally,
to provide drive-by download protection, allow download/upload of
executables and archive files (.zip and .rar), but force users to
acknowledge that they are transferring a file so that they notice
that the browser is attempting to download something they were not
aware of. For policy rules that allow general web browsing, be stricter
with your file blocking because the risk of users unknowingly downloading
malicious files is much higher. For this type of traffic, attach
a more strict file blocking profile that also blocks portable executable
(PE) files.
You can define your own custom File Blocking profiles
or choose one of the following predefined profiles when applying
file blocking to a Security policy rule. You can clone and edit
the predefined profiles, which are available with content release
version 653 and later, and then follow
File Blocking profile safe transition
steps to preserve application availability as you transition
to
best practice file blocking settings:
basic file blocking—Attach this profile
to the Security policy rules that allow traffic to and from less
sensitive applications to block files that are commonly included
in malware attack campaigns or that have no real use case for upload/download.
This profile blocks upload and download of PE files ( .scr, .cpl, .dll,
.ocx, .pif, .exe) , Java files (.class, .jar), Help files (.chm,
.hlp) and other potentially malicious file types, including .vbe,
.hta, .wsf, .torrent, .7z, .rar, .bat. Additionally, it prompts
users to acknowledge when they attempt to download encrypted-rar
or encrypted-zip files. This rule alerts on all other file types
to give you complete visibility into all file types coming in and
out of your network.
strict file blocking—Use this stricter
profile on the Security policy rules that allow access to your most
sensitive applications. This profile blocks the same file types
as the other profile, and additionally blocks flash, .tar, multi-level
encoding, .cab, .msi, encrypted-rar, and encrypted-zip files.
These
predefined profiles are designed to provide the most secure posture
for your network. However, if you have business-critical applications
that rely on some of the applications that are blocked in these
default profiles, you can clone the profiles and modify them as
necessary. Make sure you only use the modified profiles for those
users who need to upload and/or download a risky file type. Additionally,
to reduce your attack surface, make sure you are using other security
measures to ensure that the files your users are uploading and downloading
do not pose a threat to your organization. For example, if you must
allow download of PE files, make sure you are
sending all unknown PE files to WildFire foranalysis.
Additionally, maintain a strict URL filtering policy to ensure that
users cannot download content from web sites that have been known
to host malicious content.