Set Up File Blocking

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) you will want to 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 will notice that the browser is attempting to download something they were not aware of. For policy rules that allow general web browsing, be more strict with your file blocking because the risk of users unknowingly downloading malicious files is much higher. For this type of traffic you will want to 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. The predefined profiles, which are available with content release version 653 and later, allow you to quickly enable 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 that 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.
  1. Create the file blocking profile.
    1. Select
      Objects
      Security Profiles
      File Blocking
      and
      Add
      a profile.
    2. Enter a
      Name
      for the file blocking profile such as
      Block_EXE
      .
    3. (
      Optional
      ) Enter a
      Description
      , such as
      Block users from downloading exe files from websites
      .
    4. (
      Optional
      ) Specify that the profile is
      Shared
      with:
      • Every virtual system (vsys) on a multi-vsys firewall
        —If cleared (disabled), the profile is available only to the Virtual System selected in the
        Objects
        tab.
      • Every device group on Panorama
        —If cleared (disabled), the profile is available only to the Device Group selected in the
        Objects
        tab.
    5. (
      Optional—Panorama only
      ) Select
      Disable override
      to prevent administrators from overriding the settings of this file blocking profile in device groups that inherit the profile. This selection is cleared by default, which means administrators can override the settings for any device group that inherits the profile.
  2. Configure the file blocking options.
    1. Add
      and define a rule for the profile.
    2. Enter a
      Name
      for the rule, such as
      BlockEXE
      .
    3. Select
      Any
      or specify one or more specific
      Applications
      for filtering, such as
      web-browsing
      .
      Only web browsers can display the response page (continue prompt) that allows users to confirm their Choosing any other application results in blocked traffic for those applications because there is no prompt displayed to allow users to continue.
    4. Select
      Any
      or specify one or more specific
      File Types
      , such as
      exe
      .
    5. Specify the
      Direction
      , such as
      download
      .
    6. Specify the
      Action
      (
      alert
      ,
      block
      , or
      continue
      ). For example, select
      continue
      to prompt users for confirmation before they are allowed to download an executable (.exe) file. Alternatively, you could
      block
      the specified files or you could configure the firewall to simply trigger an
      alert
      when a user downloads an executable file.
    7. Click
      OK
      to save the profile.
  3. Apply the file blocking profile to a security policy rule.
    1. Select
      Policies
      Security
      and either select an existing policy rule or
      Add
      a new rule as described in Set Up a Basic Security Policy.
    2. On the
      Actions
      tab, select the file blocking profile you configured in the previous step. In this example, the profile name is
      Block_EXE
      .
    3. Commit
      your configuration.
  4. To test your file blocking configuration, access an endpoint PC in the trust zone of the firewall and attempt to download an executable file from a website in the untrust zone; a response page should display. Click
    Continue
    to confirm that you can download the file. You can also set other actions, such as
    alert
    or
    block
    , which do not provide an option for the user to continue the download. The following shows the default response page for File Blocking:
    fileblock-RespPg.png
  5. (
    Optional
    ) Define custom file blocking response pages (
    Device
    Response Pages
    ). This allows you to provide more information to users when they see a response page. You can include information such as company policy information and contact information for a Helpdesk.
    When you create a file blocking profile with the
    continue
    action, you can choose only the
    web-browsing
    application. If you choose any other application, traffic that matches the security policy will not flow through the firewall because users are not prompted with an option to continue. Additionally, you need to configure and enable a decryption policy for HTTPS websites.
    Check your logs to determine the application used when you test this feature. For example, if you are using Microsoft SharePoint to download files, even though you are using a web-browser to access the site, the application is actually
    sharepoint-base
    , or
    sharepoint-document
    . (It can help to set the application type to
    Any
    for testing.)

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