Decryption Breaks Palo Alto Dynamic Updates

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Decryption Breaks Palo Alto Dynamic Updates

L3 Networker

I'm having an issue where my Decryption policy is breaking my Palo Alto Dynamic Updates.  When I turn on decryption, and then attempt to download an Antivirus, Applications and Threats, or Wildfire update, I'm given the message "Invalid content image, Failed to download file". 


When I turn decryption off, the updates work perfectly.   This seems odd to me because SSL Decryption Exclusion already has predefined exclusions for these Palo Alto services, such as wildfire, etc. 


Otherwise, my decryption policy is working as expected and doing its job.  


I'm reading through the PAN OS Admin Guide documentation, as I'm new to PA and this is my first NGF setup.  Any suggestions on how to fix this would be much appreciated!






Accepted Solutions

I was able to fix the issue using SSL Decryption Exclusions!  The necessary FQDN's to exclude I found here:

I just copied and added everything listed as per the screenshot attached below.


Now downloads work perfectly, with decryption turned on!


Thanks everyone for your input!



Screen Shot 2021-04-28 at 12.04.19 PM.png



View solution in original post


Cyber Elite
Cyber Elite

Hi @RSteffens ,

Have you tried to disable "Verify update server identity" under Device > Setup > Services?

I know it is not good idea to disable this, but you can try to see if you disable it for a moment, can you get updates.

In my FW I don't see default decrtyption exception for "". You can try to add decryption exclusion for this FQDN and enable the verification again. It is possible that you will need to add aditional exceptions, but I am really not sure.

L1 Bithead

With decryption enabled, I would hit the "Check Now" link to refresh the cache.  As @Astardzhiev mentioned, you'll need to uncheck the "Verify update server identity" since the firewall uses cert pinning and will throw an "Unknown CA" error once the firewall-signed cert comes in, and usually results in a communcation error.  Really, it's better to just bypass decryption for Palo updates and keep the verify the server box checked.  


This problem usually causes a unknown communication error versus the invalid content image error.


Some things dont/cant be decrypted without breaking. Put in a no decrypt policy prior to your decrypt one for these updates.




L3 Networker

Thanks for your helpful replies!


I tried updating to PANOS 10 thinking that could possibly help, but it didn’t change anything. 


Good catch,, was not in the default decryption exclusions list.  I added it, committed, ran a “check now”, and attempted to download latest update, but still error out.  The error I’m getting now is different upon upgrading to PANOS 10, it simply says “Failed to download file”. 


I even unchecked “Verify Update Server Identity”, committed, ran a “check now”, and still get the same error as above (!?).


The only thing that fixes the issue is if I don’t decrypt my management zone, where I’m using a data port as management interface, with applicable service routes configured.  When that zone is NOT decrypted, updates are fine.  When I decrypt it, updates don’t work. 


How do most people handle this? You mentioned its best just to bypass decryption for Palo updates, which is what I want to do.  But the manual says that for sites that break decryption, the proper place to do it is SSL Decryption Exclusion.  Are there any other FQDN's that people are excluding there to make this work?  I could also try a decryption policy exclusion, but manual says that's only for sites you don't want to decrypt, not those which break decryption. Not sure why they make a difference between them. 

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