The Riddle

“MySQL client leaks
like a riddle”

The Riddle is a critical security vulnerability found in Oracle's MySQL 5.5 and 5.6 client database libraries. The vulnerability allows an attacker to use man riddle in the middle for breaking SSL configured connection between MySQL client and server.

This vulnerability is a very critical security hole because it affects MySQL — a very popular SQL database — and SSL connection which is by its definition secure.

“The Riddle is a very critical security vulnerability”

How can I be sure that this is a real security vulnerability?

Are you blind? Don't you see the above logo? It is an indisputable fact that it is a critical vulnerability available on the Internet. If you are still in doubt, look again and properly! This vulnerability has an iconic name and also its own website, which classifies it as an undisputed critical vulnerability. Moreover, it was assigned a CVE number CVE-2017-3305. Therefore, you should start panicking, NOW!

I'm feeling that I have a BACKRONYM déjà vu. Is it possible?

No, it's impossible. Every single vulnerability available on the Internet is unique. If you think it is similar to the BACKRONYM then look into Oracle's MySQL release notes. Issue described by the BACKRONYM is fixed in the MySQL 5.5.49 and 5.6.30. Release notes don't lie and are always correct.


Is it OpenSSL related?

No, not this time. The Riddle isn't related to the OpenSSL project.

Is it related to Linux kernel?

No, the Riddle has nothing to do with Linux kernel.

So, to which application it is related?

To Oracle's MySQL.

Does it have a CVE number?

Yes, CVE-2017-3305.

What does the name Riddle stand for?

It is a BACKRONYM for the Ridiculous Database Library Exploit.

Should I panic?

Immediately, it is a critical vulnerability available on the Internet.

Who discovered it?

The Riddle was discovered by Pali Rohár.

Should there be another Q&A?

No. Why? The Name and the logo are enough for describing any critical vulnerability available on the Internet.

Should I read the following Technical section?

No, you shouldn't. Why should somebody be interested in the boring technical details? The majority of people doesn't understand them.

Technical section


What is the real problem?

MySQL client library doesn't verify if security of the connection matches the parameters specified by the user before starting negotiation of the authentication with MySQL server. After the BACKRONYM vulnerability had been discovered, it was fixed by Oracle in MySQL 5.7. Security update for the stable MySQL 5.5.49 and 5.6.30 versions consisted of adding a verification of security parameters after the authentication process was finished. Since, it is done after the authentication man riddle in the middle attack together with SSL-downgrade attack can be used by the attacker to steal login data for immediate authentication and login to the MySQL server. Ridiculous part is that MySQL client doesn't report any SSL related error when MySQL server declines to authenticate a user and instead reports unencrypted error message send by the server. Furthermore, the error message is controlled by the attacker, when the riddle in the middle attack is active.

How can the attack look like?

The attacker needs to sit with riddle in the middle of the MySQL client and MySQL server and needs to have the ability to modify MySQL protocol communication. Due to (not fully) secure password authentication scheme which MySQL protocol uses, attacker can catch the server nonce from properly secured SSL connection with MySQL server and then forward it to the client via non-secure plain text connection. In this phase, the client doesn't do any verification of security parameters and it also doesn't verify if the other side that sent the the nonce really knows the password (or have ability to verify if supplied data are correct). Thus, the client doesn't report any problem that SSL connection isn't used and it generates authentication response. The response is sent back to other side (to the attacker) without any complains via insecure plain text mode. The attacker then finds in the riddle authentication response, sends it to the real MySQL server and voilà attacker has access to MySQL server database. Afterwards, attacker sends some error message to the client and the client propagates it to the user. The error message can contain arbitrary string and the client doesn't show any problems related to disabled SSL mode even when SSL mode was explicitly set to required. The user's password isn't disclosed as a result of the attack. The attacker can authenticate to MySQL server without the password only once as the server nonce is always (or should be) different. If authentication scheme were more robust (e.g. SCRAM), then this attack wouldn't be possible. It remains to be seen whether Oracle will be willing to switch authentication scheme to something more robust after this vulnerability was discovered and reported.

Which versions of the libraries are affected?

All versions of MySQL 5.5 and 5.6 client libraries (at the time of writing of this article). Note that MariaDB client libraries aren't affected by this vulnerability as MariaDB developers fixed BACKRONYM properly and verification of the security parameters is done before sending user credentials. Furthermore, all the programs which use MySQL or MariaDB client library incorrectly are also affected.

How do I verify if a program which uses MySQL/MariaDB is affected?

Oracle in MySQL 5.5.54 documentation (archived) demonstrates how to enforce SSL encryption via function mysql_connect_ssl_check(). The code example in the documentation is incorrect as it introduces a vulnerability to your program! In the example, the check whether SSL was established is done after starting the authentication process. If your MySQL program uses the recommendation or directly the code example provided by Oracle, then your program is affected by Riddle vulnerability independently of MySQL client library. Therefore, fixing MySQL client library isn't enough and MySQL program must be fixed too.

How do I check if my system is affected by this defect?

You are affected if you are using MySQL client in any version 5.5 or 5.6 or you are using affected program as described above and you depend on SSL encryption over untrusted network where attacker can apply riddle in the middle.

How can I mitigate this problem?

You have couple of options. The best way would be to stop using the affected libraries, either by upgrading your MySQL client to version 5.7 or by switching from MySQL to MariaDB client. You can also apply MariaDB patch for the BACKRONYM vulnerability to your MySQL client. Note that MySQL client is backward compatible and version 5.7 can connect to MySQL server 5.6 or 5.5 without any problems. So, you just need to upgrade the client without touching the server part. Another option is to stop relaying on SSL enforced encryption by MySQL and create your own correctly encrypted secure tunnel. You can use e.g. socat program which can create a bidirectional SSL tunnel or use any other secure tunnel based on SSH, VPN or IPSec. The last option is to apply ostrich effect and wait until Oracle fixes MySQL client libraries and starts distributing them to you. In that case, you should expect that you could be victim of a attack.

How do I use SSL encryption properly?

SSL (resp. TLS, as SSL v2/v3 is already broken but name SSL is commonly used for TLS protocol) implementation or protocol itself isn't affected by this vulnerability. The whole problem is how MySQL client uses SSL encryption. Men in the middle attack is very common for SSL and to prevent it, client must verify if SSL tunnel was correctly established with correct server and not with some attacker's server. It means that client must verify SSL certificate announced by the server and also that the certificate is really owned by the server. If the connection to MySQL server is SSL encrypted but MySQL client doesn't verify certificate (correctly!), then man in the middle attack is still possible and downgrade attack is needed. The Riddle vulnerability shows that MySQL client does whole verification at wrong a time — after the authentication was finished. Not before. So, enforcing SSL mode isn't enough, you also need to tell MySQL client how it must verify server's SSL certificate. Either that it is signed by really trusted certificate authority or that it matches server's certificate directly.

Are there some implementations of riddle in the middle already?

Yes, there is my proof of concept script written in Perl. It starts riddle on localhost:3307 and expects that MySQL server is running on localhost:3306. If you connect with affected client to localhost:3307, then riddle will catch and steal authentication information, connects to real MySQL server on localhost:3306 and executes SQL for returning number of all tables.

Example which expects that MySQL server is already running on localhost:

Start riddle in the middle server:

$ perl
Connect with your MySQL client to riddle, replace user and password:
$ mysql --ssl-mode=REQUIRED -h -P 3307 -u user -ppassword
If you provided correct user and password, then riddle connects to the server, executes SQL and writes output:
SELECT COUNT(*) FROM information_schema.TABLES --> 121
MySQL client just receives a nice error message sent by riddle:
ERROR 1045 (28000): Access denied: MITM attack


  • 2017-02-01 - me - Discovered the vulnerability
  • 2017-02-04 - me - Contacted Debian Security team because defect was present in Debian's library
  • 2017-02-06 - me - Provided POC perl script
  • 2017-02-06 - Debian & Oracle - Oracle person CCed by Debian Security team passed the information on upstream
  • 2017-02-10 - me - Requested information about the state and progress of the reported vulnerability
  • 2017-02-16 - Debian - Asked about the state again, since there was no answer from Oracle
  • 2017-02-23 - me - Issued another request about the current state and announced date of public disclosure to 2017-02-28 due to Oracle's inactivity
  • 2017-02-23 - Debian - Suggested to disclose the vulnerability as upstream has failed to respond
  • 2017-02-24 - Debian - Contacted Oracle team again
  • 2017-02-25 - Oracle - Answered that they were not aware of this issue, even though it was already passed on to them on 2017-02-06 and I inquired 4 times about the progress
  • 2017-02-27 - Oracle - Answered that they will provide response quickly
  • 2017-02-28 - me - Requested the current state again as Oracle hasn't respond yet
  • 2017-02-28 - Oracle - Answered that will have response shortly
  • 2017-02-28 - me - Reminded them that it was the day of public disclosure and offered them postponing the disclosure for a few days
  • 2017-02-28 - Oracle - Accepted an offer to postpone the disclosure date to the end of week
  • 2017-03-01 - me - Requested the state of the reported vulnerability again because Oracle have not provided any information of progress yet (after month!)
  • 2017-03-02 - Oracle - Sent information (for the first time) that they were actively working on this issue and asked me to keep it confidential until the end of April
  • 2017-03-02 - me - Rejected postponing disclosure date for another two months because one month should have been enough to fix the issue and users should have been informed about this vulnerability ASAP
  • 2017-03-02 - Oracle - Informed me that it is hard to fix the reported issue and requested everybody involved to keep this issue confidential
  • 2017-03-03 - me - Repeated rejection of postponing the disclosure date for another two months and offered them postponing the disclosure date for one week
  • 2017-03-03 - Oracle - Hasn't stated if they wanted to postpone the disclosure, but offered inclusion of my name into a credit section if I kept the issue confidential
  • 2017-03-11 - me - Announced to Oracle, Debian Security team, Red Hat Security team and SUSE Security team that final public disclosure is 2017-03-17 (no more postponing)
  • 2017-03-17 - me - Announced the vulnerability to the oss-sec mailing list

As you can see, communication with Oracle is very hard. For ordinary people without a big company standing behind them, it probably doesn't make any sense filing reports of security vulnerabilities. After one month, Oracle have done absolutely nothing. They even wanted to postpone the disclosure date for another two months as they are probably incompetent to handle the security issues in their products. The only thing which Oracle offered as a reward if I do not disclose this issue was an inclusion of my name to some Oracle credit section. It is probably the last thing which would a developer or a security expert want to see.

Conclusion: Reporting bugs to Oracle is useless (even those which are security related) if you are not a Oracle customer. They can perfectly ignore any reports and they would be very happy if nobody knew about it so they don't have to fix the bugs. It looks like immediate public disclosure is the best responsible solution for the users as it is the only way how to protect them and let them know immediately what should be done if they are affected.


Email address: middle at riddle dot link