Sectigo CA Chain Decryption Issues

[paul.carroll]

Due to the recent expiration of the Sectigo RSA CA cert (https://support.sectigo.com/articles/Knowledge/Sectigo-AddTrust-External-CA-Root-Expiring-May-30-202...) and our Palo firewall SSL decryption policy configuration to block expired certificates we are noticing that any website that is publishing the old expired CA chain (for example netaoc.org.uk) is being blocked due to them publishing an expired cert.

This is obviously working as expected however it's difficult for me to come into contact with each website hosting one of these invalid CA chains to get them to resolve the issue while our users experience issues and I manually exclude the sites from decryption.  I of course could turn off expired certificate blocking however this something I would rather not do.

I have noticed that web browsers like Chrome when not running through decryption are handling this issue just fine as they seem to look up the new correct CA certificate themselves and use that.  Is there a way I can configure out Palo to act in the same way or am I stuck being reliant on the web admins of the individual sites to correct their chain issues?

[RobinClayton]

Yes we are seeing this issue

Some customers are reporting it too when accessing one of our websites, but that's an external problem

I can't replicate it accessing our site externally.

I don't think it's necessarily a web hoster problem, our chain looks valid, and the certificate was only generated with it's chain in December.

I have logged a support case, I suggest you do the same.

[paul.carroll]

The only reason I think it's a chain issue from the sites host is if you check the website with a tool like https://whatsmychaincert.com/ it will report that the site is delivering an invalid chain but it implies that modern web browsers will transparently fix this issue for the end user.

[RobinClayton]

The fact that https://support.sectigo.com fails as well leads me to believe that the test site is not able to correctly process the request.

[kaschekotov]

Also, please note: https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g0000008UFBCA2

[Sec101]

This is an issue for us too.   Why isn't Palo updating these?   Does the palo check all the chains for these, apparently Sectigo is saying that the cross signed certificate is enough to stop an error for these?

[RobinClayton]

From PA Support

"From a quick search, I was able to see that multiple issues have been reported with respect to Sectigo Certificates Expiration.

As a workaround,you can either allow untrust cert or exclude the website from decryption which is causing issue.

PA has updated with the latest CA certification, so as of now no action needed on PA certificate store. If server chain is not updated till now then that might cause issue here.

Please let me know if you have any further queries or concerns regarding the case."

Awaiting their guidance on why the store is not up to date.

Rob

[kalakai]

According to this twitter thread, the issue is with how OpenSSL handles (or doesn't handle) validating certificate chains. I believe that the PAN firewalls use OpenSSL for certificate validations which is why the firewall fails to see that the server's certificate is actually valid.

As a workaround, this is what we did:

1. Create a custom URL category "Expired Certificate Bypass"
   Objects > Custom Objects > URL Category
2. Clone the decryption profile object and uncheck "Block sessions with expired certificates"
   Objects > Decryption > Decryption Profile
3. Clone the decryption rule and use the new decryption profile and url category you just created
   Policies > Decryption

This is not ideal or scalable but it works for business critical sites.

[benlangberg]

We had been running with a separate exclusion list, our helpdesk became overwhelmed with requests and cert issues. As of this post we have disabled "Block sessions with expired certificates"

Monitoring this discussion for further updates. 

[thomaswiesner]

I will do exactly the same "Benlangberg"