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.
- Create the file blocking profile.
- SelectandObjectsSecurity ProfilesFile BlockingAdda profile.
- Enter aNamefor the file blocking profile such asBlock_EXE.
- (Optional) Enter aDescription, such asBlock users from downloading exe files from websites.
- (Optional) Specify that the profile isSharedwith:
- Every virtual system (vsys) on a multi-vsys firewall—If cleared (disabled), the profile is available only to the Virtual System selected in theObjectstab.
- Every device group on Panorama—If cleared (disabled), the profile is available only to the Device Group selected in theObjectstab.
- (Optional—Panorama only) SelectDisable overrideto 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.
- Configure the file blocking options.
- Addand define a rule for the profile.
- Enter aNamefor the rule, such asBlockEXE.
- SelectAnyor specify one or more specificApplicationsfor filtering, such asweb-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.
- SelectAnyor specify one or more specificFile Types, such asexe.
- Specify theDirection, such asdownload.
- Specify theAction(alert,block, orcontinue). For example, selectcontinueto prompt users for confirmation before they are allowed to download an executable (.exe) file. Alternatively, you couldblockthe specified files or you could configure the firewall to simply trigger analertwhen a user downloads an executable file.
- ClickOKto save the profile.
- Apply the file blocking profile to a security policy rule.
- Selectand either select an existing policy rule orPoliciesSecurityAdda new rule as described in Set Up a Basic Security Policy.
- On theActionstab, select the file blocking profile you configured in the previous step. In this example, the profile name isBlock_EXE.
- Commityour configuration.
- 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. ClickContinueto confirm that you can download the file. You can also set other actions, such asalertorblock, which do not provide an option for the user to continue the download. The following shows the default response page for File Blocking:
- (Optional) Define custom file blocking 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.DeviceResponse PagesWhen you create a file blocking profile with thecontinueaction, you can choose only theweb-browsingapplication. 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 actuallysharepoint-base, orsharepoint-document. (It can help to set the application type toAnyfor testing.)
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