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BitDefender blocking NoMachine connection

Boog00001

Hello,
I have two remote PCs, A and B. I remote to PC A then use NoMachine to connect to PC B. A while back I was trying to add a firewall rule to only allow a NoMachine on port 4000 from a specific IP address belonging to PC A.
I added the rule, and immediately after adding it I was disconnected from the NoMachine connection and now I can no longer connect to PC B from PC A.

I have PC B air gapped, there is no Gateway set, so there is no internet access, only LAN. I have a feeling that I know the answer, but is there anyway I can reset, or turn off BitDefender on PC B from a LAN connection from PC A?

RDP won't work because it is disabled on PC B. I also tried several ways of connecting like using port 445 and 135. Does any one have any ideas?

Thanks

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Comments

Alexandru_BD

Hello,

If I understand this correctly, the firewall rule added on PC B has unintentionally blocked the NoMachine connection from PC A. I think the problem is that, since PC B is air-gapped and has no Internet access, there isn't a way to remotely disable or reset the firewall through Bitdefender. The firewall configuration would normally need to be changed directly on that PC.

If you can obtain local access to PC B, I would suggest the following:

Open Bitdefender and temporarily disable the firewall
Test the NoMachine connection again
If the connection works, re-enable the firewall and go to the firewall rules section
Locate the rule that was created for NoMachine and either delete it or edit it
When recreating the rule, make sure the NoMachine executable is allowed and that the remote address corresponds to PC A's LAN IP address. If you also restrict the connection by port, verify that the rule allows the correct TCP/UDP traffic required by your NoMachine configuration

You may also want to check the network adapter settings in Bitdefender and make sure the LAN is set as trusted home-office type network and that Stealth Mode is not preventing communication with other devices on that LAN. If this feature is enabled, turn it off.

I would not recommend trying to regain access using ports 445 or 135 unless remote administration through those Windows services had already been deliberately configured beforehand. Opening additional Windows management ports is unlikely to bypass the Bitdefender rule and could unnecessarily increase the attack surface…

So, if NoMachine was the only remote-management method enabled on PC B, physical/local access to the machine will most likely be required this time. Once access is restored, it may also be worth enabling a secondary management method for situations like this before applying restrictive firewall rules.

Let us know how it goes.

Regards

Boog00001

Thanks for the detailed and thoughtful reply. I thought that the only way to fix the problem would be hands on. Unfortunately that remote computer is 1500 miles away and I won’t be there until October.
Also there’s no one I would trust to give access to the house where the computer is located.

Luckily this is not a PC that I absolutely have to have access to at this time. Yes I have learned a lesson about keeping a remote access option open. I thought I was securing the PC, but I made it too secure!

Thanks again.

Dave