topic Re: PA inbound decryption in General Topics

PA inbound decryption

blabla — Sun, 11 Mar 2018 17:09:08 GMT

PA drop (decrypt-error, policy-deny) packet when client present a certificate (SMTP STARTTLS).

PAN OS version: 8.1

Test cases

1) Client cert TRUSTED, TLS 1.2 with ECDHE-RSA-AES256-GCM-SHA384

Client send Certificate Verify TLS payload

openssl s_client -starttls smtp -crlf -tls1_2 -cert trusted-cert.pem -key private.key -cipher 'ECDHE-RSA-AES256-GCM-SHA384' -connect SMTP_HOST:25

result: Connection reset by PA (decrypt-error, policy-deny)

2) Client cert UN-TRUSTED, TLS 1.2 with ECDHE-RSA-AES256-GCM-SHA384

Client send Certificate Verify TLS payload

openssl s_client -starttls smtp -crlf -tls1_2 -cert un-trusted-cert.pem -key un-private.key -cipher 'ECDHE-RSA-AES256-GCM-SHA384' -connect SMTP_HOST:25

result: Connection reset by PA (decrypt-error, policy-deny)

3) Client cert ANONYMOUS, TLS 1.2 with ECDHE-RSA-AES256-GCM-SHA384

Client NOT send Certificate Verify TLS payload

openssl s_client -starttls smtp -crlf -tls1_2 -cipher 'ECDHE-RSA-AES256-GCM-SHA384' -connect SMTP_HOST:25

result: IT`s WORK (OK)

================================================================================================

Attached captured packets pictures

decrypt error: client tls payload

decrypt error: starttls flow

OK: client tls payload

OK: starttls flow

Please help, thanks.

Re: PA inbound decryption

Remo — Sun, 11 Mar 2018 17:23:59 GMT

Hi @blabla

As far as I know, inbound decryption or decryption in general on a paloalto networks firewall does not support connections with client certificates.

Re: PA inbound decryption

blabla — Sun, 11 Mar 2018 19:20:29 GMT

Hi @Remo

This is not client cert based auth. In this case client is google smtp server, wich during sending email over STARTTLS (TLS 1.2 ECDHE-RSA-AES256-GCM-SHA384) for my smtp server, presents his client`s certificate (trusted), that verify my smtp server. The problem is PA drops (policy-deny) packets in this case. In that case inbound decryption does not properly work and does not check incoming smtp traffic. Why?

thanks for answer

Re: PA inbound decryption

Remo — Sun, 11 Mar 2018 19:37:23 GMT

Hi @blabla

In that case, when this is not client cert auth, I need to ask you to explain me why you specify a keyfile in the s_client command?

Do you allow connections that cannot be decrypted in the decryption profile attached to the decryption rule? And you wrote that this problem happens with 8.1 - was it working as expected prior to the upgrade?

Re: PA inbound decryption

blabla — Sun, 11 Mar 2018 20:08:50 GMT

openssl s_client -starttls smtp -crlf -tls1_2 -cert trusted-cert.pem -key private.key -cipher 'ECDHE-RSA-AES256-GCM-SHA384' -connect SMTP_HOST:25

This command just simulates behavior of google smtp server when it sends email (over TLS) to my server. In this case trusted-cert.pem file is trusted certificate like as in google smtp server.

========================================================

openssl s_client -starttls smtp -crlf -tls1_2 -cert un-trusted-cert.pem -key un-private.key -cipher 'ECDHE-RSA-AES256-GCM-SHA384' -connect SMTP_HOST:25

This command just simulates like previous command but uses untrusted (self signed) certificate (just for experiment).

========================================================

openssl s_client -starttls smtp -crlf -tls1_2 -cipher 'ECDHE-RSA-AES256-GCM-SHA384' -connect SMTP_HOST:25

This command just simulates like previous command but doesnt use cert and key (ANONYMOUS, generated by openssl), in this case openssl doesnt send client certificate and decryption goes right. But google smtp always sends his certificate when sending email (over STARTTLS) to my smtp server.

=======================================

>>Do you allow connections that cannot be decrypted in the decryption profile attached to the decryption rule?

Yes, all policy rules allow, decription profile Min version: SSLv3 Max version: MAX, all block options unchecked, not block.

>>And you wrote that this problem happens with 8.1 - was it working as expected prior to the upgrade?

I had PANOS version 7.1. The problem didnt solve. I upgrated from 7.1 to 8.0 version. The problem didnt solve. Finally, I upgrated from 8.0 to 8.1, but the problem didnt solve.

Thanks for answer.

Re: PA inbound decryption

blabla — Sun, 11 Mar 2018 20:16:20 GMT

After all upgrades i reimport my server certificate and private key.

Re: PA inbound decryption

Remo — Sun, 11 Mar 2018 21:35:39 GMT

@blablawrote:
After all upgrades i reimport my server certificate and private key.

And it still does not work right?

Re: PA inbound decryption

blabla — Sun, 11 Mar 2018 21:53:20 GMT

Yes!

Re: PA inbound decryption

blabla — Wed, 28 Mar 2018 17:43:45 GMT

Solved!

Client (google smtp server) send certificate when my smtp server ask. In this case inbound decryption not work!!!

I disable postfix configuration option smtpd_tls_ask_ccert = no, and fine work.