The open-source project behind the widely used Joomla content management system has issued a patch for a vulnerability that is now being widely used by hackers.
Sucuri, a company that specializes in securing websites, wrote on Monday that attackers have been trying exploit the flaw for the last two days.
As of Monday, Sucuri said "the wave of attacks is even bigger, with basically every site and honeypot we have being attacked. That means that probably every other Joomla site out there is being targeted as well."
The vulnerability, which affects Joomla versions 1.5 to 3.4.5, involves the user agent string, which is information transmitted by a browser to a Web server when a user visits a Web page.
The user agent string includes the browser type and version and the computer's operating system and version. It is used by Web servers to deliver an appropriate version of a website, such as a mobile versus a desktop version.
Attackers are "doing an object injection via the HTTP user agent that leads to a full remote command execution," Sucuri said.
Because many websites use Joomla, it presents an attractive target. If a Joomla site is compromised, attackers may be able to plant malicious code on a page or redirect people to other malicious sites.
Users are advised to upgrade to version 3.4.6, which is available here. Joomla is used by companies including eBay, Peugeot and Barnes & Noble.