Multiple vulnerabilities were discovered in Drupal core.
A bug in the installer code was identified that allows an attacker to re-install Drupal using an external database server under certain transient conditions. This could allow the attacker to execute arbitrary PHP code on the original server.
This vulnerability is mitigated by the fact that the re-installation can only be successful if the site's settings.php file or sites directories are writeable by or owned by the webserver user. Configuring the Drupal installation to be owned by a different user than the webserver user (and not to be writeable by the webserver user) is a recommended security best practice. However, in all cases the transient conditions expose information to an attacker who accesses install.php, and therefore this security update should be applied to all Drupal 7 sites.
For sites using the core OpenID module, an information disclosure vulnerability was identified that allows an attacker to read files on the local filesystem by attempting to log in to the site using a malicious OpenID server.
Drupal 6 is not affected.
Install the latest version:
If you are unable to deploy the security release immediately, removing or blocking access to install.php is a sufficient mitigation step for the arbitrary PHP code execution vulnerability.
Also see the Drupal core project page.