How do I use "openssl s_client" to test for (absence of) SSLv3 support?

Question

In order to mitigate the "Poodle" vulnerability, I'd like to disable SSLv3 support in my (in this case, TLS, rather than HTTPS) server. How can I use openssl s_client to verify that I've done this?

Answer 1

OpenSSL s_client

To check if you have disabled the SSLv3 support, then run the following

openssl s_client -connect example.com:443 -ssl3

which should produce something like

3073927320:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1258:SSL alert number 40
3073927320:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure:s3_pkt.c:596:

meaning SSLv3 is disabled on the server. Otherwise the connection will established successfully.

Nmap

Alternatively, you can use nmap to scan server for supported version:

# nmap --script ssl-enum-ciphers example.com
Starting Nmap 6.47 ( http://nmap.org ) at 2014-10-15 03:19 PDT
Nmap scan report for example.com (203.0.113.100)
Host is up (0.090s latency).
rDNS record for 203.0.113.100: edge.example.com
Not shown: 997 filtered ports
PORT    STATE SERVICE
80/tcp  open  http
443/tcp open  https
| ssl-enum-ciphers: 
|   **SSLv3: No supported ciphers found**
|   TLSv1.0: 

Answer 2

On a side note you can use nmap with ssl-enum-ciphers script as follows

nmap --script ssl-enum-ciphers -p 443 example.com

You will get a response like this.

PORT    STATE SERVICE
443/tcp open  https
| ssl-enum-ciphers: 
|   SSLv3: 
|     ciphers: 
|       TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_RSA_WITH_RC4_128_MD5 - strong
|       TLS_RSA_WITH_RC4_128_SHA - strong
|     compressors: 
|       NULL
|   TLSv1.0: 
|     ciphers: 
|       TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_RSA_WITH_RC4_128_MD5 - strong
|       TLS_RSA_WITH_RC4_128_SHA - strong
|     compressors: 
|       NULL
|   TLSv1.1: 
|     ciphers: 
|       TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - strong
|     compressors: 
|       NULL
|   TLSv1.2: 
|     ciphers: 
|       TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 - strong
|     compressors: 
|       NULL
|_  least strength: strong

As you can see it lists all the supported versions of ssl/tls as well as the cipher suites

Answer 3

If just SSLv3 is disabled, you can also force openssl s_client to use only TLS:

openssl s_client -connect exmaple.com:443 -tls1

Answer 4

I created this test for the availability of the SSLv3 protocol. There is probably a better way to search for a string that also shows that CBC ciphers are in use, but most people just seem to want to know if SSLv3 is available at all.

A few things to note:

• Written for the bash on Mac OS X so can't say for sure it will work everywhere
• Uses gtimeout vs. timeout since Mac is weird about those core utils
• allexternal.txt is a file with one hostname or IP per line

script:

for ip in `awk '{print $1}' < allexternal.txt`; do
    if gtimeout 30 openssl s_client -connect $ip:443 -ssl3 | grep -q 'Protocol  : SSLv3' ; then
        echo $ip SSLv3 detected >> sslv3output;
    else
        echo $ip SSLv3 NOT detected >> sslv3output;
    fi;
done

Answer 5

It's worth noting that the -ssl3 option in OpenSSL now has to be enabled at compile time. If you're running on pre-compiled binaries then the option may not be available. See this issue: https://github.com/openssl/openssl/issues/6801

An alternative tool is testssl.sh. This checks for protocols, ciphers and selected vulnerabilities: https://github.com/drwetter/testssl.sh