SSL Client Certification Alert 46 Unknown CA

We are seeing 'Alert 46 Unknown CA' as part of the initial TLS handshake between client & server. From a wireshark capture, the 1st Client Hello is visible, followed by the 'server hello, certificate, server key exchange, certificate request, hello done'. As part of this exchange, TLS version 1.2 is agreed, along with the agreed cypher. The next packet in the flow is an ACK from the source, followed by Alert (Fatal), Description: Certificate Unknown. I cannot see anywhere in the capture a certificate provided by the client

This behaviour occurs regardless of the client authentication/client certificate setting (ignore/request/require).

I have ran openssl s_client -connect x.x.x.x:443 as a test (from the BIG-IP) and I see the server side certs and 'No client certificate CA names sent' which is expected as no client cert sent.

The end client has not reinstalled the client certificate as yet (3 day lead time).

Are there any additional troubleshooting steps I can undertake to confirm the client is either rejecting the server certificate and therefore not returning the client certificate?

Kind Regards

spalande
Apr 15, 2021
Cool. If it's a web based application and browser is the client then yes it would be present. But if it's API call with server to server communication they might need to install it explicitly.

Also, other thing I would check on the F5 clientssl profile, if CA cert is correctly added to the chain (in case it's not bundled with the server cert)? Meanwhile, please verify that part as well.
NUCUSER
Apr 21, 2021
Update - Thanks for all your suggestions, most helpful!! This turned out to be a client side cert password issue, client cert re-installed and now working.

Rebecca_Moloney
Admin
Apr 18, 2023
Glad you were able to find a solution! Just popping in after the fact to share a few popular TLS related DevCentral articles in case anyone finds them helpful:

Decrypting TLS traffic on BIG-IP

TLS Stateful vs Stateless Session Resumption

What is Mutual TLS (mTLS)?
Lidev
MVP
Apr 14, 2021
Hi,
You can try to decode TLS records with SSL dump to better understand the root cause and see which part fail.
Please refer below link to get information :
K10209: Overview of packet tracing with the ssldump utility

Also, uncheck the Generic Alert options on your Client SSL profile and increase the log level SSL on your F5 to obtain perhaps more details in the ltm log.

Regards
NUCUSER
Cirrus
Apr 14, 2021
Hi Lidev

I already tried SSL dump and it did not appear to provide any more data than a standard wireshark capture. I will revisit.

Generic alerting is disabled/unchecked. The only alerts I see are generic SSL handshake failed messages for TCP source > dest (status code 1260013)

Thanks
- Lidev
  MVP
  Apr 15, 2021
  Have you try to enable SSL debug logging on the BIG-IP ?
  tmsh modify /sys db log.ssl.level value Debug
  - NUCUSER
    Cirrus
    Apr 15, 2021
    Hi, we are running version 15 so low level debugging is enabled by default. I did try via tosh and it provided no additional logging
    
    Thanks
spalande
Nacreous
Apr 15, 2021
Please check if client has server certificate's CA (intermediate certificate) installed in it's trust store. If not, please share the CA cert (public key of the intermediate certificate) to the client so that it can trust the server certificate.
NUCUSER
Cirrus
Apr 15, 2021
Hi Sanjay, Thanks. We have asked the client to confirm however intermediate cert is digicert so would expect they have.
- spalande
  Nacreous
  Apr 15, 2021
  Cool. If it's a web based application and browser is the client then yes it would be present. But if it's API call with server to server communication they might need to install it explicitly.
  
  Also, other thing I would check on the F5 clientssl profile, if CA cert is correctly added to the chain (in case it's not bundled with the server cert)? Meanwhile, please verify that part as well.
  - NUCUSER
    Cirrus
    Apr 16, 2021
    Hi Sanjay, is there anyway to test confirm the certificate chain on the server side?
    
    The SSL certificate chain comprises of /common/wildcard.company123.com.crt/Common/wildcard.company123.com.key /Common/digicert_inter.crt
    
    The Intermediate CA chain is specified in the client ssl profile (trusted certificate authorities) is XYX_Int_CA_Chain.crt. This crt is present on the F5 along with the wildcard.company123.com.crt cert
    
    Thanks
jaikumar_f5
MVP
Apr 16, 2021
,

This is a client side issue for not having the required intermediate or root certificate in the trust store of client machine. In LTM you'll just SSL Handshake failed logs, but in pcap you'll see this, alert coming from Client to LTM, SSL Fatal alert, RST.

level fatal,
value unknown_ca

Work with your client support team & have required keystore updated.
- NUCUSER
  Cirrus
  Apr 16, 2021
  cheers..
  - spalande
    Nacreous
    Apr 16, 2021
    Root certificate is not needed on the client end it's just a intermediate CA cert.
NUCUSER
Cirrus
Apr 21, 2021
Update - Thanks for all your suggestions, most helpful!! This turned out to be a client side cert password issue, client cert re-installed and now working.