Drupal, which is a volunteer open-source project whose software is used by websites such as The White House and the Economist, said all of 7.x releases prior to 7.32 are affected, according to an advisory.
Administrators should update to version 7.32. If that is not possible, a patch is available for the "database.inc" file that fixes the problem.
Drupal uses a database abstraction API (application programming interface) that filters harmful SQL (structure query language) queries, but the vulnerability (CVE-2014-3704) can allow an attacker to send malicious queries that could be executed. These so-called SQL injection attacks are among the most common type of attacks against a website.
"Depending on the content of the request this can lead to privilege escalation, arbitrary PHP execution or other attacks," Drupal wrote.
The flaw can be exploited by anonymous users, and there are now proof-of-concept instructions circulating that show how to exploit it, according to a FAQ document.
"While we do not have reports of actual usage, the nature of this vulnerability is such that the attack can be difficult to detect," it said.
The vulnerability was reported last month by Sektion Eins, which is a PHP-focused security firm in Germany that was hired by an unnamed client to audit its code, Drupal wrote. Drupal's security team often gets reports from those kind of audits, it said.
Drupal debated whether to release a patch early, but opted to stick to its normal schedule for releasing security updates due to its Amsterdam conference at the end of September.
"We felt that it would be better to use the regularly scheduled date which also happened to be the first date when the Drupal community would be likely to have time to focus on the upgrade," the organization wrote.
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