Conflict between Comodo Free Firewall and Avast! Free Antivirus


I’ve gotten several BSODs recently and both WhoCrashed and Windbg have said the cause is cmdguard.sys, the driver for Comodo’s Firewall Virtual Sandbox. I ran Comodo’s diagnostics and sent the reports to their Technical Support people. I just heard back from them, and they said that the problem is Comodo is conflicting with Avast!. They instructed me to uninstall Avast!. I really don’t want to do this as I like and am happy with Avast! and it’s performance.

So, I would like to know if anyone else is running Comodo Free Firewall (I’m using the current version, 10.4.2233.), and if so, are you having any problems with BSODs? Are there any insights into how to resolve this issue besides uninstalling Avast! and using another free antivirus program?

If you’ve had problems with Avast! and Comodo Free Firewall and have switched to a different free antivirus program that you’ve had success with, what free antivirus program are you using?

I’ve had other BSODs also but the Comodo driver was not indicated to be the cause.

I’m using Windows 8.1 and the most current version of Avast! but the BSODs occurred with the previous version of Avast! also.

Thank you very much for any information you can provide.

As a search on here, and most Forums will tell you, running two or more AVs is not a good idea. Most AVs do not play well with other AVs. Comodo, and Avast, are no exception.
Please uninstall one or the other, you cannot run both.

Hi John,

Thank you for the quick reply.

I appreciate the information and am aware that you should not have 2 antivirus programs installed. Please note that I’m using the COMODO Free Firewall only which does not have an antivirus component, not the full COMODO Internet Security software package which has the antivirus component.


I just wanted to provide an update on what I did and the current status. I uninstalled Avast! Free Antivirus and installed COMODO Internet Security Premium since it has an antivirus component. However, I wasn’t sure if my email was being scanned, so I contacted COMODO Support. Unfortunately, I found out that because my email uses SSL/TLS connections, COMODO will not scan my email. It also doesn’t work with my email client, Mozilla Thunderbird. Consequently, I cannot use COMODO Internet Security Premium. I can only use COMODO Free Firewall, and, therefore, will need to find an antivirus only program that works with COMODO Free Firewall.

I did run Avast!'s support tool and submitted the generated file to them to see if they have any solutions to the issue as I really want to keep using COMODO Free Firewall. However, any other suggestions as to how resolve this issue are more than appreciated.

Thanks a million.

Just to let you know I’m using Avast Free and Comodo Firewall and have no problems at all.

Hi Dumper1,

Thanks so much for letting me know that you’re using the same combination of security software that I’m using without any problems. I submitted the file generated by Avast!'s Support Tool to their Technical Support people yesterday and am waiting to hear back from them to find out if they have the same diagnosis as the COMODO’s technical support people and if they have any suggestions as to how to resolve the problem based on a different diagnostic file.

Perhaps since you’re not having the problem (and I imagine there are others out there who are also using this combination of security software and not having the problem), there is something else going on in my computer, too.

Don’t forget to have Comodo in Avast’s File Exclusions, that was advice given quite some time ago when there used to be a conflict between the two.

Hi Dumper1,

Thanks so much, again, for the information. I had not added COMODO to Avast!'s File Exclusions because of information I read in an Avast! support forum post. However, since you have added these exclusions and have not had any BSODs, I have added the following exclusions in Avast!:

C:\Program Files (x86)\Comodo*
C:\Program Files\COMODO*

Can you please let me know if I have done this correctly? I followed the pattern I used for the exclusions I added for Malwarebytes.

Thanks so very much. I truly appreciate you help!

Best regards,

my buddy1998

Yes that looks good, fingers crossed you get no more BSOD’s. :slight_smile:

Hi Dumper1,

Thanks so very much for confirming my exclusions look good and for keeping your fingers crossed I don’t get any more BSOD’s. :slight_smile: I sincerely appreciate both. I’ve got my fingers (and toes) crossed, too.

Best regards,


I confirm problem with Avast and Comodo FIREWALL. I have latest Win 10 64bit, latest Comodo Fw (I do not use CIS) and the latest Avast version has problem with Comodo Fw. Earlier version of Avast worked without problem.
Avast says: There is installed another antivirus software on your PC.

There is any solutions? Sorry for my English.

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Avast thinks Comodo AV or Comodo Internet Security (which also has the AV ) is installed but it is only the firewall. It’s an error by Avast. Please report this as a bug at the Avast forums.


radek178 - Thanks a million for your post. I’m running Windows 8.1 64 bit, but I get the same results in the Compatibility Check when I run Avast’s Smart Scan.

EricJH - Thanks so very much for the information and advice. I just submitted a support ticket with Avast Technical Support.

Best regards,


Thank you for reporting back and submitting the bug with Avast.

Hi EricJH,

You are very welcome. I just checked my email, and there was no reply from them. When I get a definitive answer, I will let the forum know.

Best regards,



I just received a reply to the support ticket I opened with Avast!'s Technical Support, and I wanted to post their reply here.

Best regards,


Reply from Avast! Technical Support

"Thank you for contacting AVAST Software s.r.o. with your concerns and sorry for the late response.

I discussed this problem with our developers and they informed me that this detection is correct. There can be conflicts between Comodo Firewall and some features of Avast (Home Network Security).

It isn’t a big compatibility problem like it would be if an ordinary second antivirus would be running, but the warning is correct in general.

If you are only using the essential parts of Avast antivirus (Web, File System and Mail shields), you can ignore this message.

We are sorry for the inconvenience. If you have any further questions, don’t hesitate to contact me again."