Posts Tagged ‘s_client’

Openssl s_client to verify you installed your certificate properly and list of return codes

I use openssl’s s_client option all the time to verify if a certificate is still good on the other end of a web service. So I figured I’d put a couple of common options down on paper for future use.

openssl s_client -connect www.google.com:443    #HTTPS
openssl s_client -starttls ftp -connect some_ftp_server.com:21      #FTPES
openssl s_client -starttls smtp -crlf -connect smtp.gmail.com:25     #SMTP
openssl s_client -starttls smtp -crlf -connect smtp.gmail.com:587    #SMTPS
openssl s_client -starttls imap -crlf -connect some_imap_server:143  #IMAP
openssl s_client -connect imap.gmail.com:993     #IMAPS
openssl s_client -connect pop.gmail.com:995      #POPS


You can use the…

-showcerts

..option to display the entire certificate chain which is useful for validating your intermediates.
You’ll also get an official “Verify return code” which can be used to diagnose any SSL/TLS issues. Here’s a quick list of common return codes:

(I blatantly grabbed this from here!)

Error Code

Error Text

Description

0 Ok The operation was successful.
2 Unable to get issuer certificate The issuer certificate of a looked up certificate could not be found. This normally means the list of trusted certificates is not complete.
3 Unable to get certificate CRL The CRL of a certificate could not be found.
4 Unable to decrypt certificate’s signature The certificate signature could not be decrypted. This means that the actual signature value could not be determined rather than it not matching the expected value, this is only meaningful for RSA keys.
5 Unable to decrypt CRL’s signature The CRL signature could not be decrypted. This means that the actual signature value could not be determined rather than it not matching the expected value. Unused.
6 Unable to decode issuer public key The public key in the certificate SubjectPublicKeyInfo could not be read.
7 Certificate signature failure The signature of the certificate is invalid.
8 CRL signature failure The signature of the certificate is invalid.
9 Certificate is not yet valid The certificate is not yet valid. the notBefore date is after the current time.
10 Certificate has expired The certificate has expired. that is the notAfter date is before the current time.
11 CRL is not yet valid The CRL is not yet valid.
12 CRL has expired The CRL has expired.
13 Format error in certificate’s notBefore field The certificate notBefore field contains an invalid time.
14 Format error in certificate’s notAfter field The certificate notAfter field contains an invalid time.
15 Format error in CRL’s lastUpdate field The CRL lastUpdate field contains an invalid time.
16 Format error in CRL’s nextUpdate field The CRL nextUpdate field contains an invalid time.
17 Out of memory An error occurred trying to allocate memory. This should never happen.
18 Self signed certificate The passed certificate is self signed and the same certificate cannot be found in the list of trusted certificates.
19 Self signed certificate in certificate chain The certificate chain could be built up using the untrusted certificates but the root could not be found locally.
20 Unable to get local issuer certificate The issuer certificate could not be found. this occurs if the issuer certificate of an untrusted certificate cannot be found.
21 Unable to verify the first certificate No signatures could be verified because the chain contains only one certificate and it is not self signed.
22 Certificate chain too long The certificate chain length is greater than the supplied maximum depth. Unused.
23 Certificate revoked The certificate has been revoked.
24 Invalid CA certificate A CA certificate is invalid. Either it is not a CA or its extensions are not consistent with the supplied purpose.
25 Path length constraint exceeded The basicConstraints pathlength parameter has been exceeded.
26 Unsupported certificate purpose The supplied certificate cannot be used for the specified purpose.
27 Certificate not trusted The root CA is not marked as trusted for the specified purpose.
28 Certificate rejected The root CA is marked to reject the specified purpose.
29 Subject issuer mismatch The current candidate issuer certificate was rejected because its subject name did not match the issuer name of the current certificate. Only displayed when the -issuer_checks option is set.
30 Authority and subject key identifier mismatch The current candidate issuer certificate was rejected because its subject key identifier was present and did not match the authority key identifier current certificate. Only displayed when the -issuer_checks option is set.
31 Authority and issuer serial number mismatch The current candidate issuer certificate was rejected because its issuer name and serial number was present and did not match the authority key identifier of the current certificate. Only displayed when the -issuer_checks option is set.
32 Key usage does not include certificate signing The current candidate issuer certificate was rejected because its keyUsage extension does not permit certificate signing.
50 Application verification failure An application specific error. Unused.

 

Additional links:
https://www.openssl.org/docs/apps/s_client.html

https://www.openssl.org/docs/apps/ciphers.html

vsftpd, FTPES & CentOS 5.5 part 2

 

This is the second part of my FTPES, vsftpd & CentOS article. In the first part I walked you thru how I built a certificate, sent the CSR off to my CA and finally, modified the vsftpd.conf file. In this part I’ll show you how to test the service via command-line so you can actually see the certificate and how to punch a hole thru your FW because the data part of your FTP session is now encrypted.

First, let’s talk about verifying the configuration. One of the obvious things you can do is open up a command prompt session and attempt to log into your ftp server. Once connected, does it accept an anonymous connection? Was that what you wanted? Also, was the plain jane ftp command allowing you to log in or did you get a 331 error, “Non-anonymous sessions must use encryption.” If you’ve configured it correctly it shouldn’t allow you to login at all. So how do you test it using encryption? By using openssl w/ s_client of course! Use…

openssl s_client -starttls ftp -connect yourserver.example.com:21

This will allow you to not only log into your server using encryption via command-line but also verify that you’ve got the proper certificate & certificate chain installed. I personally tried connecting w/ out the starttls option but wasn’t successful (instead I get a “SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol” error message. I beleive this is because I’m using vsftpd in explicit mode not impicit mode.) The openssl s_client command can also be used for a number of other encrypted services for debugging certificates which is extremely helpful!

So you’ve verified that FTPES does work on the local LAN but doesn’t seem to work thru your FW. This is where passive ftp comes into play because your FTP traffic is now encrypted and your FW can’t do an inspection to determine which port is going to be used next and open it up for you ahead of time. Most FWs come with some sort of FTP inspect feature but we just killed it because that data is totally encrypted now and it’s unable to sniff the FTP traffic and sense which port needs to be opened. You won’t have to turn on passive FTP because it’s on by default with vsftpd. You should specify the port range and I also turned on pasv_address too:

pasv_enable=YES
pasv_addr_resolve=YES
pasv_address=yourserverhere.example.com
pasv_min_port=63000
pasv_max_port=65535

Once done, this will force your vsftpd server to use a port range of 63000 to 65535 for data connections. Alot of the commands I used above can be found w/in the man page for vsftpd.conf (along with their default values!)

Now you just need to open up that same range on your FW device (NOTE: Each FW is going to be different!) On my Cisco Adaptive Security appliance (ASA) I’m defining an object-group first for the port range like such:

object-group service ftp_passive tcp
  description ftp passive range
  port-object range 63000 65535

Then I use that port range in my outside ACL for inbound traffic like such:

access-list outside_access_in extended permit tcp any host YOUR_PUBLIC_IP object-group ftp_passive
.
.
.

Just be sure to use your public IP address for ‘YOUR_PUBLIC_IP’ in the above ACE. Now when it comes to ACL rules there’s tons of different ways to allow traffic so I won’t go into much more detail here other than how I punched a hole thru my FW to allow the encrypted vsftpd data channel traffic through.

That’s about it folks. Remember, if you’re having problems with your configuration, break it down into simple pieces and troubleshoot it that way versus trying to eat the entire problem at once!

-Q

Oh, almost forgot. Here’s a couple links that might be helpful!

http://en.wikipedia.org/wiki/Ftp
http://en.wikipedia.org/wiki/FTPES
http://it.toolbox.com/blogs/unix-sysadmin/troubleshooting-ssltls-mail-services-29266
http://www.wowtutorial.org/tutorial/26.html
http://vsftpd.beasts.org/
http://www.openssl.org/docs/apps/s_client.html
http://blogs.iis.net/robert_mcmurray/archive/2008/11/10/ftp-clients-part-2-explicit-ftps-versus-implicit-ftps.aspx

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