IO::Socket::SSL client checking server certificate - perl

Question

I want to use server certificate when connecting with IO::Socket::SSL client.
What I did is to extract certificate first,
openssl s_client -showcerts -connect 127.0.0.1:443 </dev/null 2>/dev/null|openssl x509 -outform PEM >/tmp/localhost.crt
-----BEGIN CERTIFICATE-----
MIID1jCCAr6gAwIBAgICBH8wDQYJKoZIhvcNAQELBQAwgZ8xCzAJBgNVBAYTAi0t
MRIwEAYDVQQIDAlTb21lU3RhdGUxETAPBgNVBAcMCFNvbWVDaXR5MRkwFwYDVQQK
DBBTb21lT3JnYW5pemF0aW9uMR8wHQYDVQQLDBZTb21lT3JnYW5pemF0aW9uYWxV
bml0MRAwDgYDVQQDDAdiaWdnZXIyMRswGQYJKoZIhvcNAQkBFgxyb290QGJpZ2dl
cjIwHhcNMTYwODA0MDUyMTA5WhcNMTcwODA0MDUyMTA5WjCBnzELMAkGA1UEBhMC
LS0xEjAQBgNVBAgMCVNvbWVTdGF0ZTERMA8GA1UEBwwIU29tZUNpdHkxGTAXBgNV
BAoMEFNvbWVPcmdhbml6YXRpb24xHzAdBgNVBAsMFlNvbWVPcmdhbml6YXRpb25h
bFVuaXQxEDAOBgNVBAMMB2JpZ2dlcjIxGzAZBgkqhkiG9w0BCQEWDHJvb3RAYmln
Z2VyMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBALSJplghG5oD5FhU
1v9IkE8z0k/7g1W29GhUXwf7IKzzjplIgpsZ+Ya/OtDbIctSYZ3gNEMyj+LdlvEW
6rCDCSTULPWwdjuSdHmUiFyeJm+QBtnMIp9I3P7zPCd+W9Cyhue911tXCHiQMg+E
ZNi2WlqnBGf/5l6VFRVMxQTEbTRiTPaH9VFnuyCKcJTk9ephZmZRgfeNmXT7BRjG
nmsYa0jG2rh2UmJGQrJhZOZYmghbq1BL66m7yCxfknsjTHGfy7PS/c+K83fPVI0p
bcBgl0VCA7d8TX6xj4BwMec7nwdi95ISVAG3jjL11+lrlcg6UGs+bd+NVpd1PbVY
XwVcWu8CAwEAAaMaMBgwCQYDVR0TBAIwADALBgNVHQ8EBAMCBeAwDQYJKoZIhvcN
AQELBQADggEBAFkWi/C8UlEqXPO0aDrn78teYzh3D0BIuhB4vawDSUuz68Clq41u
bMLIbdWZS244NFLeWAYJf4k0WDk7/nz5pxWLqlDg4LumZxNOUeSWUSbantRn6NnQ
rJrWZi6gJFgeC/34t3k+XvtmbDl5a2L213TxOtnSZJty/ZxUr3v3Z3Dp5+kfTAyR
xlD/gOlAEHgrOjwv1XofVb5pALPjzGj9gAfe/bpMEG4GORgtJzFz/teugL4yZ4Mk
sk6BhIBd1hTWJXUfvH6GPaoieug46CAkolmvc0q2nfMiU+hZOkDE1rtyqS5XMF5t
O2nma+wuMF6z/naEXFPq65sFOHI8vz+oEaQ=
-----END CERTIFICATE-----
and then connect using ssl_client.pl from examples folder,
ssl_client.pl -d10 --ca /tmp/localhost.crt localhost:443
DEBUG: .../IO/Socket/SSL.pm:2757: new ctx 17132992
DEBUG: .../IO/Socket/SSL.pm:643: socket not yet connected
DEBUG: .../IO/Socket/SSL.pm:645: socket connected
DEBUG: .../IO/Socket/SSL.pm:667: ssl handshake not started
DEBUG: .../IO/Socket/SSL.pm:700: using SNI with hostname localhost
DEBUG: .../IO/Socket/SSL.pm:735: request OCSP stapling
DEBUG: .../IO/Socket/SSL.pm:769: call Net::SSLeay::connect
DEBUG: .../IO/Socket/SSL.pm:2658: did not get stapled OCSP response
DEBUG: .../IO/Socket/SSL.pm:2611: ok=0 [0] /C=--/ST=SomeState/L=SomeCity/O=SomeOrganization/OU=SomeOrganizationalUnit/CN=bigger2/emailAddress=root#bigger2/C=--/ST=SomeState/L=SomeCity/O=SomeOrganization/OU=SomeOrganizationalUnit/CN=bigger2/emailAddress=root#bigger2
DEBUG: .../IO/Socket/SSL.pm:772: done Net::SSLeay::connect -> -1
DEBUG: .../IO/Socket/SSL.pm:775: SSL connect attempt failed
DEBUG: .../IO/Socket/SSL.pm:775: local error: SSL connect attempt failed error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
DEBUG: .../IO/Socket/SSL.pm:778: fatal SSL error: SSL connect attempt failed error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
DEBUG: ...inux/IO/Socket.pm:49: ignoring less severe local error 'IO::Socket::INET configuration failed', keep 'SSL connect attempt failed error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed'
DEBUG: .../IO/Socket/SSL.pm:2779: free ctx 17132992 open=17132992
DEBUG: .../IO/Socket/SSL.pm:2784: free ctx 17132992 callback
DEBUG: .../IO/Socket/SSL.pm:2791: OK free ctx 17132992
failed to connect to localhost:443: ,SSL connect attempt failed error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed at ./ssl_client.pl line 52.
This doesn't work as expected, so please suggest how to properly verify server using locally stored certificate.

Answer 1

While your certificate is self-signed (i.e. signed by itself) it is not a CA:
X509v3 extensions:
X509v3 Basic Constraints:
CA:FALSE
Because it is not a CA it is not allowed to be used as an issuer of a certificate and thus can in theory not even be used to sign itself.
This is at least the logic implemented in OpenSSL (and thus Net::SSLeay, IO::Socket::SSL). Other implementations like NSS seem to work with such certificates probably because they check if the server certificate itself is explicitly trusted. Such a check is different from only checking if it is signed by a trusted CA which is done by using the SSL_ca* options in IO::Socket::SSL (or -CAfile, -CApath arguments in openssl s_client).
Explicitly trusting a specific certificate no matter if it is self-signed, expired, revoked or whatever can be done in IO::Socket::SSL by using the SSL_fingerprint option.
Note that debugging IO::Socket::SSL in this case does not help a lot since the logic in this case is implemented in OpenSSL. There is some small indicator where it is going wrong:
DEBUG: ... ok=0 [0] .../CN=bigger2/emailAddress=root#bigger2 .../CN=bigger2/emailAddress=root#bigger2
This debug statement is called from the verification callback. ok=0 [0] indicates that this callback was called with ok=0 at level certificate level 0, i.e. that the built-in validation of OpenSSL did not consider this certificate as valid.