In this blog post, I will discuss the CVE-2016-6662 vulnerability, how to tell if it affects you, and how to prevent the vulnerability from affecting you if you have an older version of MySQL.
I’ll also list which MySQL versions include the vulnerability fixes.
As we announced in a previous post, there are certain scenarios in Percona Server (and MySQL) that can allow a remote root code execution (CVE-2016-6662).
Vulnerability approach
The website legalhackers.com contains the full, current explanation of the CVE-2016-6662 vulnerability.
To summarize, the methods used to gain
root
privileges require multiple conditions:
- A remote (or even local) MySQL user that has
FILE
permissions (or
SUPER
, which encompasses all of them).
- Improper OS files/directories permissions around MySQL configuration files that allow the MySQL system user access to modify or create new configuration files.
- Several techniques alter the MySQL configuration to include loading a malicious shared library.
The techniques currently described require
FILE
or
SUPER
privileges, but also include the currently undisclosed CVE-2016-6663 (which demonstrates how to alter the configuration without
FILE
privileges).
- Have that malicious shared library loaded when MySQL restarts, which includes the code that allows privilege escalation.
Fixed versions
MySQL fixes
MySQL seems to have already released versions that include the security fixes.
This is coming from the release notes in MySQL 5.6.33:
- For mysqld_safe, the argument to
--malloc-lib now must be one of the directories /usr/lib, /usr/lib64, /usr/lib/i386-linux-gnu, or /usr/lib/x86_64-linux-gnu. In addition, the --mysqld and --mysqld-version options can be used only on the command line and not in an option file. (Bug #24464380)
- It was possible to write log files ending with
.ini or .cnf that later could be parsed as option files. The general query log and slow query log can no longer be written to a file ending with .ini or .cnf. (Bug #24388753)
- Privilege escalation was possible by exploiting the way
REPAIR TABLE used temporary files. (Bug #24388746)
You aren’t affected if you use version 5.5.52, 5.6.33 or 5.7.15.
Release notes: 5.5.52, 5.6.33, 5.7.15
Percona Server
The way Percona increased security was by limiting which libraries are allowed to be loaded with
LD_PRELOAD
(including
--malloc-lib
), and limiting them to
/usr/lib/
,
/usr/lib64
and the MySQL installation base directory.
This means only locations that are accessible by
root
users can load shared libraries.
The following Percona Server versions have this fix:
We are working on releasing new Percona XtraDB Cluster versions as well.
Future Percona Server releases will include all fixes from MySQL.
MariaDB
MariaDB has fixed the issue in 5.5.51, 10.1.17 and 10.0.27
I have an older MySQL Version, what to do now?
It is possible to change the database configuration so that it isn’t affected anymore (without changing your MySQL versions and restarting your database). There are several options, each of them focusing on one of the conditions required for the vulnerability to work.
Patch
mysqld_safe
Manually
Just before publishing this, a blogpost came out with another alternative on how to patch your server: https://www.psce.com/blog/2016/09/12/how-to-quickly-patch-mysql-server-against-cve-2016-6662/.
Database user permissions
One way to avoid the vulnerability is making sure no remote user has
SUPER
or
FILE
privileges.
However, CVE-2016-6663 mentions there is a way to do this without any
FILE
privileges (likely related to the
REPAIR TABLE
issue mentioned in MySQL release notes).
Configuration files permissions
The vulnerability needs to be able to write to some MySQL configuration files. Prevent that and you are secure.
Make sure you configure permissions for various config files as follows:
