Troubleshoot Version Errors

1. Identify version errors in the decryption logs.

   1. Select Monitor Logs Decryption.
   2. Filter decryption logs using the following queries:
      • To find all instances where the error is related to protocol versions: (err_index eq Version). The highlighted values are bitmask values.

        Error Index = Version

      • To find all instances where the protocol versions supported by the client and in the Decryption profile attached to the policy rule don't match: (error contains ‘Client and decrypt profile mismatch’).

        Error contains 'client and decrypt profile version mismatch'

   You can filter decryption logs in many ways.

   For example, to see only TLSv1.3 version errors, specify the error index and the TLS version you're looking for in the query as follows: (err_index eq Version) and (tls_version eq TLS1.3).

   To find all decryption sessions that experienced the same error, click an error message to add it to the query and remove the original query, for example:

   The hexadecimal codes or bitmasks identify the exact version that the client supports and the exact version that the Decryption profile supports.
2. Log in to the CLI to look up the bitmask values.

   To identify the TLS versions that a bitmask corresponds to, use the debug dataplane show ssl-decrypt bitmask-version <bitmask-value> CLI command.

   Example screens of this lookup:

   • Example 1 (first screenshot)
     The version errors in the first screenshot (the same errors for all three sessions) show an issue with a client and Decryption profile mismatch. The version supported by the client is represented by the 0x08 bitmask and the version supported in the Decryption profile bitmask is 0x70.

     1. admin@vm1>debug dataplane show ssl-decrypt bitmask-version 0x08
        TLSv1.0

        This output shows that the client supports only TLSv1.0.

     2. admin@vm1>debug dataplane show ssl-decrypt bitmask-version 0x70
        TLSv1.1
        TSLv1.2
        TLSv1.3

        This output shows that the Decryption profile supports TLSv1.1, TLSv1.2, and TLSv1.3, but not TLSv1.0. Now you know the issue is that the client only supports an older version of the TLS protocol and the Decryption profile attached to the decryption policy rule that controls the traffic does not allow TLSv1.0 traffic.
   • Example 2 (third screenshot)
     The version error in the second screenshot shows a different issue: a client and server version mismatch. The error indicates the supported client bitmask as 0x20:

     admin@vm1> debug dataplane show ssl-decrypt bitmask-version 0x20
     TLSv1.2

     The output shows that the client supports only TLSv1.2, which means that the server doesn't support this version. The server might only support TLSv1.3 or it might support only TLSv1.1 or lower (less secure protocols).
3. Decide what action to take.

   How you fix this error depends on the TLS versions supported by the client and server and your business needs.

   • Evaluate if you need access to the server for business or another important purpose.
   • Confirm the TLS versions that the server supports. You can use Wireshark or another packet analysis tool to find out which TLS versions the server supports.
   • You could update the client or server to support a stronger version.
   • If the client only supports a weaker TLS version, and cannot support a more secure protocol, as in Example 1, you can:
     • Let the NGFW continue to block the traffic.
     • (Not Recommended) Update the Decryption profile to allow certain TLS traffic. Continue to step 4. This option allows traffic of a specific TLS version when it matches the decryption policy rules that the profile is attached to, which is why it's not recommended.
       Don't allow access to all servers that use less secure TLS versions. Create more specific rules for cases like this.
       This may be a good course of action in a case like Example 2, where the server supports a more secure TLS protocol than the client. Then, you'd be updating the client so that it accepts a more secure TLS version, which is good for security.
     • (Most Secure option) Configure a Decryption profile that allows the weaker TLS version, but apply it to a decryption policy rule for the particular server that controls the sites, user, device, or source address (and to any similar users, devices, or source addresses so that one policy rule and profile control all of this traffic) that must use this server.
4. Identify and modify the Decryption profile associated with the policy rule that controls the session traffic.

   1. Identify the decryption policy rule that control the session traffic.

      1. Check the Policy Name column in the log (or click the magnifying glass
         next to a Decryption log entry to see the information in the General section of the Detailed Log View).
      2. Select PoliciesDecryption. Then, select the policy rule with the Policy Name above. In the examples, the policy rule is Big Brother.
   2. Identify the Decryption profile.

      Select the Options tab. Decryption profile displays the name of the Decryption profile.
   3. Edit the protocol versions supported in the Decryption profile.

      • Select ObjectsDecryptionDecryption Profile, and select the appropriate Decryption profile.
      • Select SSL Decryption SSL Protocol Settings, and then select the Min Version and Max Version that you need.
      • Click OK.
5. Commit your changes.