A publicly disclosed vulnerability in the MySQL database could allow attackers to completely compromise some servers.

The vulnerability affects "all MySQL servers in default configuration in all version branches (5.7, 5.6, and 5.5) including the latest versions," as well as the MySQL-derived databases MariaDB and Percona DB, according to Dawid Golunski, the researcher who found it.

The flaw, tracked as CVE-2016-6662, can be exploited to modify the MySQL configuration file (my.cnf) and cause an attacker-controlled library to be executed with root privileges if the MySQL process is started with the mysqld_safe wrapper script.

The exploit can be executed if the attacker has an authenticated connection to the MySQL service, which is common in shared hosting environments, or through an SQL injection flaw, a common type of vulnerability in websites.

Golunski reported the vulnerability to the developers of all three affected database servers, but only MariaDB and Percona DB received patches so far. Oracle, which develops MySQL, was informed on Jul. 29, according to the researcher, but has yet to fix the flaw.

Oracle releases security updates based on a quarterly schedule and the next one is expected in October. However, since the MariaDB and Percona patches are public since the end of August, the researcher decided to release details about the vulnerability Monday so that MySQL admins can take actions to protect their servers.

Golunski's advisory contains a limited proof-of-concept exploit, but some parts have been intentionally left out to prevent widespread abuse. The researcher also reported a second vulnerability to Oracle, CVE-2016-6663, that could further simplify the attack, but he hasn't published details about it yet.

The disclosure of CVE-2016-6662 was met with some criticism on specialized discussion forums, where some users argued that it's actually a privilege escalation vulnerability and not a remote code execution one as described, because an attacker would need some level of access to the database.

"As temporary mitigations, users should ensure that no mysql config files are owned by mysql user, and create root-owned dummy my.cnf files that are not in use," Golunski said in his advisory. "These are by no means a complete solution and users should apply official vendor patches as soon as they become available."

Oracle didn't immediately respond to a request for comments on the vulnerability.