Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am trying to do an audit of SSL enabled ports/services running on our Linux RHEL 5.3 servers . I am trying to find which ports on our servers are ssl enabled .I am not sure how to find this .I need to know how to check which ports are using ssl enabled services.

I have run commands below

lsof -i -n -P netstat -ntulp netstat -nap

but from the outputs of these i am not sure how to determine which ports are running ssl.I am not sure what to look for

Any help please , I am aware of SSLscan utility but when i run it it doesnt return any values and spits out an error ...could not open a connection to host on port 443

SSLscan It seems to work in our windows environment without any erors but not Linux .I am also aware of nmap but cannot use it in our environment for security reasons

Help please

share|improve this question

I'm not sure if there's an automated way to do this.

First, I would list all the ports that are listening and match the ports to the process/executable (for example, with netstat -t -l -p, as root to be able to see the process ID (PID)).


You'll get entries like this, where the PID is:

tcp        0      0 *:https            *:*                LISTEN      5221/apache2

This tells you which program is running on port https. (Use netstat -t -l -p -n if you just want the port number, in which case you'll see *:443 instead of *:https). This tells you that there's a socket listening on port 443. In addition, here, 5221 is the PID for apache2, so that also tells you which application is being used. Sometimes, it may not be immediately visible which application is being used (you can look at the content of /proc/5221/cmdline to see more details for example).

I would only focus on the entries that are bound to external interfaces (and ignore the localhost entries).

Typically, you may see something listening on port 22 (ssh), 80 (http), 443 (https), ...

You'll then have to test them one by one depending on the method described below.

For example echo "" | openssl s_client -connect should show an error message, since your web server wouldn't (or shouldn't) listen to SSL/TLS requests on this port, echo "" | openssl s_client -connect should work and show you some information regarding the certificate and the connection.


For up-front SSL/TLS, you can check whether it will accept a TLS ClientHello (i.e. be a TLS server from the start of the connection), but using echo "" | openssl s_client -connect hostname:port (echo "" | is optional, it will just stop openssl as soon as it has established the connection, as you probably don't want to send anything specific).

For "upgraded" SSL/TLS connections, done after a command at the application protocol level (such as STARTTLS), this can be trickier.

You can do this for by adding -starttls the_name_of_the_protocol to this openssl s_client command. According to the OpenSSL documentation, "Currently, the only supported [protocol names] are "smtp", "pop3", "imap", and "ftp"".

This won't help you for LDAP (if configured to use Start TLS and not up-front TLS), MySQL, PostgreSQL, ... For these, you may simply have to look into their respective configuration files. Automating this process would require a tool that can understand all these protocols, which can be quite difficult.

A couple of additional points, if it's for a more general security audit:

  • Enabling SSL/TLS is rarely enough. You also want to make sure it's configured properly: valid certificate, SSLv2 disabled, trying to move to the higher values of SSL/TLS (SSLv3, TLSv1.0, TLSv1.1+) by disabling older versions if your user-base is sufficiently compatible, insecure renegotiation disabled if possible, reasonably strong cipher suites.

  • Despite using the OpenSSL library, OpenSSH (and SSH in general) is not based on SSL/TLS. You might still want to keep this one, even if your policy is to use SSL/TLS-only services.

share|improve this answer
Bruno,Thanks very much i really appreciate your help but your advice is too advanced and technical for me i am a bit new to this so please break it down lol i run the first netstat command – Dominiqs Dec 9 '11 at 15:43
I've just edited my answer. What you'll need to use really depends on what you're trying to achieve with your audit and what services you're running. As I said, the likes of MySQL will be hard to test using a generic tool (you're better off with their respective clients with the right SSL/TLS options). In short, you can check that a service is willing to talk SSL/TLS from the start of the connection easily (with openssl s_connect), but it's harder to check services with protocols that can switch to SSL/TLS after (even a few) of their own protocol commands. – Bruno Dec 9 '11 at 16:03
Thanks so much extremely helpful – Dominiqs Jan 13 '12 at 14:39

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.