Decoding (encrypted) MySQL traffic with Wireshark

In a comment on my post about Using SSL with MySQL xiaochong zhang asked if it is possible to decode SSL/TLS encrypted MySQL traffic. The short answer is: It depends.

To test this we need a MySQL server which is SSL enabled. I used MySQL Sandbox to create a sandboxed 5.6.19 server. Then I used mysslgen to create the config and the certificates.

$ make_sandbox 5.6.19
$ ./mysslgen.py --config=sandboxes/msb_5_6_19/my.sandbox.cnf --ssldir=sandboxes/msb_5_6_19/ssl

This assumes there already is a extracted tarball of MySQL 5.6.19 in ~/mysql/5.6.19

The mysslgen.py script will return a message with the changes you should make in your mysqld and client sections of the my.sandbox.cnf file. Then restart the server to make it active.

For SSL to work we need to connect using TCP/IP instead of over a UNIX socket. So we connect with "./my sql -h 127.0.0.1". Now execute "\s" or "status" to see if we're indeed using SSL.

It probably looks like this:

mysql [127.0.0.1] {msandbox} ((none)) > \s
--------------
/home/dveeden/opt/mysql/5.6.19/bin/mysql  Ver 14.14 Distrib 5.6.19, for linux-glibc2.5 (x86_64) using  EditLine wrapper

Connection id:  3
Current database: 
Current user:  msandbox@localhost
SSL:   Cipher in use is DHE-RSA-AES256-SHA
Current pager:  stdout
Using outfile:  ''
Using delimiter: ;
Server version:  5.6.19 MySQL Community Server (GPL)
Protocol version: 10
Connection:  127.0.0.1 via TCP/IP
Server characterset: latin1
Db     characterset: latin1
Client characterset: utf8
Conn.  characterset: utf8
TCP port:  5619
Uptime:   1 hour 32 min 48 sec

Threads: 1  Questions: 18  Slow queries: 0  Opens: 67  Flush tables: 1  Open tables: 60  Queries per second avg: 0.003
--------------

Now disconnect and start the trace.

sudo tcpdump -i lo -s 65535 port 5619 -w /tmp/mysql.pcap

First connect w/o SSL: "./my sql -h 127.0.0.1 --skip-ssl". And then with SSL: "./my sql -h 127.0.0.1"
Stop the tcpdump session and start wireshark and open the mysql.pcap file. Now we can inspect the protocol. If MySQL is using the default port (3306) then wireshark will automatically decode the traffic, but now we have to use 'Decode as...' to tell wireshark this is MySQL traffic. The server greeting packet and the login request should now be visible. In the login request there are client capability flags, one of the flags indicates 'Switch to SSL after handshake' and should be set for the SSL session.

Both SSL and non-SSL sessions will use the same port and start an unencrypted session. The encrypted session will switch to SSL after the handshake. This is a bit like STARTTLS for IMAP. The current version of the MySQL protocol dissector is not (yet) aware of some of the new information in the initial handshake. So the information for the authentication plugins and connection attributes is not decoded yet. The documentation about the protocol can be found in the MySQL Internals manual.

So that's the plaintext part. Now we get to the SSL part. In my setup the default cipher suite which is used for SSL is  DHE-RSA-AES256-SHA. With OpenSSL's ciphers command we can get some more details:

$ openssl ciphers -v 'DHE-RSA-AES256-SHA'
DHE-RSA-AES256-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA1

This means that SHA 1 is use for the MAC part and that AES-256 is used for encryption and the keyexchange is done with DH (Diffie-Hellman). This poses a problem as DH will generate a session key, and we don't have that in the traffic dump as it's not sent over the network. We could use gdb (and maybe a debug trace?) to get the DH keys out, but for now we have an easier solution: use a different cipher suite.

So start tcpdump again and run "./my sql -h 127.0.0.1 --ssl-cipher=AES256-SHA". This cipher uses RSA for keyexchange instead of DH. This means everything we need is send over the network or is present in the SSL certificate and/or key.

Now start wireshark again and use 'Decode as...' and choose SSL. Then go Edit→Preferences→Protocols→SSL→'RSA key list' and add the server's SSL key. Now you should see the decoded traffic.

So decoding SSL/TLS encrypted MySQL traffic is possible. But you need to have:

• All traffic since the beginning of the TCP/IP connection
• The server's SSL key
• The DH session key if DH is used. (you might want to read about Forward secrecy (PFS) if you're interested in the details).