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How to Block UltraSurf (From 11.03 onwards) using Application Control Advanced and DPI-SSL

03/26/2020 59 15976

DESCRIPTION:

Ultrasurf allows end users to circumvent gateway security devices like web filters and secure web gateways in order to surf the Internet without restrictions.

RESOLUTION:

This article describes how to block UltraSurf versons 11.03 and above using App Control Advanced signatures.

Please Note: SID 7 is a firmware-based App Control signature and requires SonicOS 5.8.1.8-57o and above

Summary of configuration required to effectively block UltraSurf

Enable DPI-SSL Client Inspection (CI)
Enable Application Firewall under DPI-SSL CI
Enable App Control Advanced signatures (see list below)

The following table lists the application group or the signature IDs used to block UltraSurf:

Category	Application Name	Signature Name	Signature ID
PROXY-ACCCESS	Encrypted Key Exchange	Random Encryption(Skype,UltraSurf,Emule)	5
PROXY-ACCCESS	Encrypted Key Exchange	UDP Random Encryption(UltraSurf)	7
PROXY-ACCCESS	Non-SSL Traffic over SSL Port	Traffic Anomaly Detection	6
PROXY-ACCCESS	UltraSurf	UltraSurf Application Group
PROXY-ACCCESS	HTTP Proxy	HTTP Proxy Application Group

NOTE

Enabling the above signatures has the unintended consequence of blocking outbound encrypted UDP packets which includes Skype traffic, SonicWall GVC connections and/or encrypted Syslog traffic to a GMS server. This is due to SID # 7 which blocks encrypted UDP packets. In the case of GVC connections this shouldn't be considered a drawback. Instead, it's a way to control unauthorised outbound VPN connections. Administrators can exclude remote gateway IP addresses and/or GMS server IP address from SID # 7.

This article illustrates how to enable the above signatures and how to exclude IP addresses from SID # 7.

Procedure:

Enabling DPI-SSL Client Inspection

NOTE:

Enabling DPI-SSL Client Inspection would entail a restart of the appliance; thereafter, DPI-SSL would re-sign all SSL/TLS connections passing through it. This could cause disruption in the network. Read the following article before enabling DPI-SSL CI : How to Configure Client DPI-SSL (Video Tutorial and Article)

Login to the SonicWall Management GUI.
Navigate to the DPI-SSL | Client SSL page.
Under General settings, enable the check box Enable SSL Client Inspection
Enable the check box against Application Firewall
Click on Accept at the top to save the changes

Enabling Signature ID 5,6 & 7.

Navigate to the Firewall | App Control Advanced page.
Check the box against Enable App Control.
Under Lookup Signature ID, enter 5, 6 and 7 one after another and click on the configure button for each signature.
In the Edit App Control Signature window, set Block and Log to Enable.
Click on OK to save the settings.

Enabling Application Signature Group - UltraSurf

On the App Control Advanced page, select Category as PROXY-ACCESS
Select Ultrasurf under Application
Click on the configure button to bring up the Edit App Control App window.
Select Enable under Block and Log.
Click on OK to save.

Enabling Application Signature Group - HTTP Proxy

On the App Control Advanced page, select Category as PROXY-ACCESS
Select HTTP Proxy under Application
Click on the configure button to bring up the Edit App Control App window.
Select Enable under Block and Log.
Click on OK to save.

Enabling Application Control on LAN zone

Navigate to Network | Zones
Click on the configure button under the zone where you want enable App Control.
Check Enable App Control Service.

Excluding gateway IP addresses of SonicWall GVC from SID # 7

Signature ID 7 blocks encrypted UDP packets. SonicWall GVC connection uses UDP 4500 & 500. To allow GVC connections, exclude the gateway IP addresses of the GVC connection from SID # 7.

How to Test:

From a host behind the SonicWall start UltraSurf. UltraSurf will try to contact its servers and eventually fail.

The following App Control messages will be logged under Log | View when UltraSurf traffic is detected and blocked:

Resolution for SonicOS 6.5

This release includes significant user interface changes and many new features that are different from the SonicOS 6.2 and earlier firmware. The below resolution is for customers using SonicOS 6.5 firmware.