How to Block TeamViewer on your Network

TeamViewer is an application for online meetings, web conferences, file & desktop sharing over computers. TeamViewer is famous mostly for its Remote Control sharing feature. This allows users to get remote access over other computer screens. Two users can access each other’s computer with all controls.

This remote administration and conferencing application are available for almost all operating systems, i.e., Windows, iOS, Linux, Blackberry, etc. The main focus of this application is accessing and granting controls of others’ computers. The presentation and conferencing features are also included.

As TeamViewer plays with online controls over computers, you might doubt its security features. Well no worries, TeamViewer comes with 2048-bit RSA based encryption, with key exchange and two-factor authentication. It also enforces password reset option if any unusual login or access is detected.

Contents

• How to Block TeamViewer on your Network
• #1. DNS Block
• #2. Ensure Clients Connection
• #3. Block access to IP Address Range
• #4. Block the TeamViewer Port
• #5. Group Policy Restrictions
• #6. Packet Inspection

How to Block TeamViewer on your Network

Still, you may somehow want to block this application from your network. In this article, we will explain to you how to do so. Well, the thing is TeamViewer does not require any configuration or any other firewall to connect two computers. You only need to download the .exe file from the website. This makes the set up for this application very easy. Now with this easy installation and access, how would you block TeamViewer on your network?

There were a lot of high volume allegations about TeamViewer users getting their systems hacked. Hackers and Criminals get illegal access.

Let us now get through the steps to block TeamViewer:

#1. DNS Block

First of all, you will need to block the DNS records resolution from the domain of TeamViewer, i.e., teamviewer.com. Now, if you are using your own DNS server, just like the Active Directory server, then this would be easy for you.

Follow the steps for this:

1. First, you need to open the DNS management console.

2. You will now need to create your own top-level record for the TeamViewer domain (teamviewer.com).

Now, you don’t have to do anything. Leave the new record as it is. By not pointing this record anywhere, you will automatically stop your network connections to this new domain.

#2. Ensure Clients Connection

In this step, you need to check if the clients can’t connect to the external DNS servers. You will need to ensure that to your internal DNS servers; only DNS connections are granted access. Your internal DNS servers contain the dummy record we created. This helps us remove the slight possibility of client checking DNS record of TeamViewer. Instead of your server, this client check is only against their servers.

Follow the steps to ensure Client connection:

1. The first step is to log in to the Firewall or your Router.

2. Now you need to add an outgoing firewall rule. This new rule will disallow port 53 of TCP and UDP from all the sources of IP addresses. It only allows the IP addresses of your DNS server.

This allows the clients only to resolve the records that you have authorised through your DNS server. Now, these authorised servers can forward the request to other external servers.

#3. Block access to IP Address Range

Now that you have blocked the DNS record, you may get relieved that connections have been blocked. But it would help if you weren’t, because sometimes, despite the DNS being blocked, the TeamViewer will still connect to its known addresses.

Now, there are ways to overcome this problem too. Here, you will need to block access to the IP address range.

1. First of all, login to your Router.

2. You will now need to add a new rule for your Firewall. This new firewall rule will disallow the directed connections to 178.77.120.0./24

The IP address range for TeamViewer is 178.77.120.0/24. This now is translated to 178.77.120.1 – 178.77.120.254.

#4. Block the TeamViewer Port

We won’t call this step as mandatory, but it is better safe than sorry. It acts as an extra layer of protection. The TeamViewer often connects on the port number 5938 and also tunnels through the port number 80 and 443, i.e., HTTP & SSL respectively.

You can block this port by following the given steps:

1. First, log in to the Firewall or your Router.

2. Now, you will need to add a new firewall, just like the last step. This new rule will disallow the port 5938 of TCP and UDP from the source addresses.

#5. Group Policy Restrictions

Now, you must consider including Group Policy Software Restrictions. Follow the steps to do it:

1. The first step is to download the .exe file from the TeamViewer website.
2. Launch the app and open the Group Policy Management console. Now you need to set up a new GPO.
3. Now that you have set up a new GPO go to User Configuration. Scroll for Window Settings and enter Security Settings.
4. Now go to the Software Registration Policies.
5. A new Hash Rule pop-up window will appear. Click on ‘Browse’ and search for the TeamViewer setup.
6. Once you’ve found the .exe file, open it.
7. Now you need to close all windows. The final step now is to link the new GPO to your domain and select ‘Apply to Everyone’.

#6. Packet Inspection

Let us now talk about when all of the above-mentioned steps fail to perform. If this happens, you will require to implement a new firewall which can perform Deep Packet Inspections and UTM (Unified Threat Management). These specific devices search the common remote access tools and block their access.

The only downside of this is Money. You will need to spend a lot of money to buy this device.

One thing that you need to keep in mind is that you are eligible to block the TeamViewer and the users at the other end are aware of the policy against such access. It is advised to have written policies as a backup.

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You can now easily block TeamViewer on your network by following the above-mentioned steps. These steps will protect your computer from other users who try to gain control over your system. It is advised to implement similar packet restrictions to other remote access applications. You are never too prepared when it comes to Security, are you?