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Sophos Firewall: v19.5 GA: Feedback and experiences

Release Post:  Sophos Firewall v19.5 is Now Available 

Old v19.0 MR1 thread:  Sophos Firewall: v19.0 MR1: Feedback and experiences 

EAP Sub thread:  SFOS v19.5 Early Access Program 

EAP 19.5 Thread:  Sophos Firewall: v19.5 EAP1: Feedback and experiences 



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  • This is indeed expected behavior of the FCI feature.  What follows is a Draft of a KB Article I'm writing (feedback welcome).



    In XG 18.0 the DPI proxy was introduced, with many more SSL/TLS scanning options and certificate protection. There are some certificate security concerns with that are blocked in most configurations, however they are allowed without any warning when using DPI mode with the decryption profile "Maximum compatibility". In these cases the XG decrypts and re-signs, creating a new certificate with its own Certificate Authority that hides potential problems that the end user should know about which that would be blocked in other configurations.

    In 19.0 a new feature was added called Forward Certificate Invalidity (FCI). This feature detects certain types of certificate invalidity and "forwards" (tells the user) about them. Because we cannot create a certificate with the same error, so we create one in a special way that we know will cause browsers to warn users. A CA is used that us unique and untrusted, and the certificate Common Name is used as the error message to tell the end user what the problem is. This changes the behavior of DPI mode with Maximum Compatibility. By signing it in the way, browsers will warn users that there is a certificate problem but will allow users to proceed and load the pages as they did in 18.0/18.5.

    The most common issue that FCI catches on the public internet is websites that do not send their entire certificate chain. When a website provides their certificate, they usually provide the certificate, the CA that signed it (usually an intermediate CA), the CA that signed that one, up to the root CA. The root CA is trusted by the browser, and the browser can verify the entire chain.

    However some websites do not provide the chain. They may provide only the certificate, or they provide the certificate and the root CA, but they do not provide the intermediate CA. While this is valid, it is not best practice and sites like ssllabs.com which rate sites will cap their score.

    If a website does not provide the chain they usually implement AIA (Authority Information Access). This is a link within the certificate that says where to download the CA that signed it.

    Some browsers (Chrome 58+, Edge, Safari) will automatically use the AIA to download the intermediate and store it for future use. Firefox 75+ uses a different mechanism called intermediate CA preloading (wiki.mozilla.org/.../Intermediate_Preloading). Older Android (pre Oreo) devices do not support any mechanism. The XG does not currently support AIA.

    If the website does not provide the full chain, the XG behavior depends on the configuration. It is important to note that v19 did not introduce blocking of sites that do not provide the full chain. The XG has always blocked these sites when using normal security, and the resolution below has always worked. The difference is that when using a decryption profile that does not block self signed certificate, invalid issuers, or many other security concerns (such as "Maximum compatibility") we used to allow the connection and sign it in a way that made it appear more secure. Now we allow but sign it in a way that appears insecure.

    How to configure the system to allow access to sites that do not provide a complete certificate chain.

    Method 1 - Do not decrypt
    Configure the domain to not be decrypted. Adding the domain to the Local TLS Exclusion List is the best option for DPI mode. Adding it to a Web Exception will exclude it for both DPI and Proxy mode.

    Method 2 - Add the Intermediate certificate to the XG CA store

    Option 1:
    Test the site in www.ssllabs.com/.../
    You should see that the grade is capped to B and the Certification Path includes an "Extra Download". In the section under Issuer there should be an AIA link.

    Option 2:
    Use a browser that is not going through the XG, or is going through the XG with HTTPS not decrypted so that you get the original certificates as presented by the site. Ask the browser to display the certificate information and the AIA link should be there. How this is displayed is browser specific.

    Once you have the AIA link, download the certificate to your computer. Then in WebAdmin go to Certificates > Certificate Authorities and Add. Choose the file.
    With the Intermediate in the CA store, the page will load in all configurations.

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  • I have updated 2 test firewalls to 19.5 today. Both have a tunnel to an XG with 19.0.1 and dynamic routing with OSPF. The first firewall has an IPSec tunnel, here the tunnel stood after the update, the OSPF negotiation basically worked (no error messages in the log), however the firewall did not distribute its own route, so the site was not reachable. Reboot and reconfigure OSPF did not help. After a rollback to 19.0.1 the OSPF worked again.
    The second firewall has a RED tunnel to the central office, there are no problems with OSPF there.
    Are there any known issues with SFOS 19.5, IPSec and OSPF?

    Ben

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  • Hi      Dev team would like to investigate why this is not working in your setup.Can you share the support access for your device/s in  Private message to me? Meanwhile some quick info on this  will help team to start with 1. config from /conf/routing/ 2. Logs: /log/csc.log , /log/ospfd.log , /log/zebra.log 3. ifconfig output 4. complete backup of the device config if available . Also If possible please provide device support access id for to login and check more. -Shrikant

  • Hi, I send you the access ID via PM. -Ben

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  • The version 19.5 has an OSPF link monitor, on my test firewall was the LAN port down and the route was not distributed. After I plugged the cable into the LAN port, the route was distributed. 

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  • Thanks Ben@Network  for providing configuration and logs to quickly analyze the problem you were facing. Good to hear that its working fine post link restore.  

  • Are there any possibilities to disable the OSPF Link monitoring?

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Reply Children
  • Yes, we are working on the same and tracking it under  NC-110203.

    Also can you share more details on use case where this will be helpful to distribute route without actual connectivity/reachability.

  • I manage many firewalls with OSPF. This problem occurred on my test firewall, which normally has no active link on the LAN interface. I use this to test the updates and to test the automation using API. This is of course not a setup that will be used like this in the real world.

    Now that I think about it, another problem might become relevant. If the switch that the firewall is connected to fails, the OSPF route would be deleted and the firewall would not be available to analyze the problem. We usually access the LAN IP of the firewall via VPN tunnel (WebAdmin or ssh) and then see what is reachable in network. This way would then be omitted. I could alternatively access via Sophos Central and open the console in WebAdmin, but then I would have to enter a password again, which I would have to type in manually.

    This can be done, but it is a different way with its own challenges. If the route is kept, we can use the normal workflow to access it.

    So it would be desirable to have at least the choice whether the link monitoring should be active or not.

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  • Thanks Ben@Network  for the details.

    We are working on the solution to provide a configurable option to end user. 

    We anticipated appliance access scenario and want to know, if this can be an issue for any other scenarios/use cases.