"Received certificate chain could not be verified. Verification status is 66" since version 3.20.0

[lc_cbhp]

After upgrading from FileZilla Client version 3.19.0 to 3.20.0, a secured connection to a ftp server is no more possible.
Status: Resolving address of lidame.lima-ftp.de
Status: Connecting to 62.113.217.13:21...
Status: Connection established, waiting for welcome message...
Status: Initializing TLS...
Error: Received certificate chain could not be verified. Verification status is 66.
Error: Could not connect to server

Version 3.20.0 added a new feature called "Stricter certificate chain validation to supplement the Tofu model". Maybe there is an bug or a side effect?
Version 3.19.0 works pretty well.

[lc_cbhp]

debug log, version 3.19.0, working

[lc_cbhp]

debug log, version 3.20.0, failure

[lc_cbhp]

The server provides a wildcard certificate for the customers.

Certificate in chain:

0:

Common Name: *.lima-ftp.de
Certificate Issuer: StartCom Class 2 Primary Intermediate Server CA

1:

Common Name: StartCom Class 2 Primary Intermediate Server CA
Certificate Issuer: StartCom Certification Authority

[Tim Kosse]

The server sends a malformed certificate chain.

For reference, see ​https://tools.ietf.org/html/rfc5246#page-48:

certificate_list
This is a sequence (chain) of certificates. The sender's
certificate MUST come first in the list. Each following

certificate MUST directly certify the one preceding it.

Your server sends 4 certificates A, B, C, D with A signed by D, C signed by B and D signed by C.

Please contact your server administrator or server hosting provider for assistance so that the certificates can be arranged in the correct order mandated by the TLS specifications.

[lc_cbhp]

Replying to codesquid:

The server sends a malformed certificate chain.

As you can see in my previous post, the servers sends the certificates in correct order.

[Tim Kosse]

Well it doesn't send them in the correct order, it's not even a wildcard certificate:

$ gnutls-cli  -s --crlf -p 21 lidame.lima-ftp.de
Processed 175 CA certificate(s).
Resolving 'lidame.lima-ftp.de'...
Connecting to '62.113.217.13:21'...

- Simple Client Mode:

220-##########################################################################
220- FTP-Zugang von www.lima-city.de
220- Es gelten unsere AGB und Regeln.
220- Lies bei Fragen oder Problemen bitte zuerst in unseren Hilfetexten nach.
220-##########################################################################
220 Dies ist ein privates System - Keine anonyme Anmeldung m▒glich.
AUTH TLS
234 AUTH TLS OK.
*** Starting TLS handshake
- Certificate type: X.509
- Got a certificate list of 4 certificates.
- Certificate[0] info:
 - subject `OU=Domain Control Validated,OU=PositiveSSL,CN=zeus.lima-premium.de', issuer `C=GB,ST=Greater Manchester,L=Salford,O=COMODO CA Limited,CN=COMODO RSA Domain Validation Secure Server CA', RSA key 2048 bits, signed using RSA-SHA256, activated `2015-09-01 00:00:00 UTC', expires `2016-08-31 23:59:59 UTC', SHA-1 fingerprint `613374289f586c3ab041ca47a71b451440530289'
        Public Key ID:
                87d79b8943d72ea8e47864752de77a856b5bb970
        Public key's random art:
                +--[ RSA 2048]----+
                |                 |
                |                 |
                |             .   |
                |         ...o.o  |
                |        S.+.o+.. |
                |        o+ + =o o|
                |       o. + =o.E.|
                |       +.. ...*..|
                |      ..o    o.o |
                +-----------------+

- Certificate[1] info:
 - subject `C=SE,O=AddTrust AB,OU=AddTrust External TTP Network,CN=AddTrust External CA Root', issuer `C=SE,O=AddTrust AB,OU=AddTrust External TTP Network,CN=AddTrust External CA Root', RSA key 2048 bits, signed using RSA-SHA1, activated `2000-05-30 10:48:38 UTC', expires `2020-05-30 10:48:38 UTC', SHA-1 fingerprint `02faf3e291435468607857694df5e45b68851868'
- Certificate[2] info:
 - subject `C=GB,ST=Greater Manchester,L=Salford,O=COMODO CA Limited,CN=COMODO RSA Certification Authority', issuer `C=SE,O=AddTrust AB,OU=AddTrust External TTP Network,CN=AddTrust External CA Root', RSA key 4096 bits, signed using RSA-SHA384, activated `2000-05-30 10:48:38 UTC', expires `2020-05-30 10:48:38 UTC', SHA-1 fingerprint `f5ad0bcc1ad56cd150725b1c866c30ad92ef21b0'
- Certificate[3] info:
 - subject `C=GB,ST=Greater Manchester,L=Salford,O=COMODO CA Limited,CN=COMODO RSA Domain Validation Secure Server CA', issuer `C=GB,ST=Greater Manchester,L=Salford,O=COMODO CA Limited,CN=COMODO RSA Certification Authority', RSA key 2048 bits, signed using RSA-SHA384, activated `2014-02-12 00:00:00 UTC', expires `2029-02-11 23:59:59 UTC', SHA-1 fingerprint `339cdd57cfd5b141169b615ff31428782d1da639'
- Status: The certificate is NOT trusted. The name in the certificate does not match the expected.
*** PKI verification of server certificate failed...
*** Fatal error: Error in the certificate.
*** Handshake has failed

[Tim Kosse]

​https://ftptest.net/ has been updated to now also show and validate the received certificate chain.