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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.

    Jump to answer
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  • Hi,

    Our Sophos Upgrade experience was terrible.

    We Upgrade a Sophos XG 125 to SFOS 19.5.0 GA-Build197 from SFOS 19.0.1 MR-1-Build365 and we lost access to the firewall and internet. We were forced to go onsite to recover.

    SFOS 19.5.0 broke all network interfaces configuration and Wireless

    No Internet access
    No VPN
    None of the WAN ports were working
    Made all Access points permanently inactive

    We had to revert to SFOS 19.0.1 MR-1-Build365, restore configuration from a backup and reconfigure Wireless Access points from scratch.

    Bad work from the Dev team.

    Very disappointed.

  • Hi Bill,

    It's unfortunate that you faced this problem. 

    Can you provide more info around it?

    a. After upgrade to v19.5 appliance come up in factory reset config? or you lost specific configuration only as mentioned above?

    b. After rollback to original firmware "SFOS 19.0.1 MR-1-Build365", it should have all configuration as is. why you had to perform backup restore.

    c. If you have opened a support case, can you provide case ID?

    d. In case not can you provide support access id. I will DM you for that.

  • Hi,

    a. It seems that 19.5 change some configuration, only ports 1 & 2 were active but not configured correctly. The 2 other wan ports were completely disabled (even the status LEDs were off)

    b. After rollback to 19.0.1 the XG 125 was very slow, and Wireless was not working so we restore a recent backup. Wireless didn’t work so we delete the access points and added and configure again.

    c. No time to do any of that.

    d. OK but please don't break anything.

    Sorry I don’t have more information. We had to recover our customer’s internet access asap.

Reply
  • Hi,

    a. It seems that 19.5 change some configuration, only ports 1 & 2 were active but not configured correctly. The 2 other wan ports were completely disabled (even the status LEDs were off)

    b. After rollback to 19.0.1 the XG 125 was very slow, and Wireless was not working so we restore a recent backup. Wireless didn’t work so we delete the access points and added and configure again.

    c. No time to do any of that.

    d. OK but please don't break anything.

    Sorry I don’t have more information. We had to recover our customer’s internet access asap.

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