On Dec. 12, security company Sucuri noted that it had seen zero-day attacks in the wild on Joomla, a popular open-source content management system (CMS). These attacks affected versions 1.5.0 through 3.4.5. The CMS presents a tempting target for cybercriminals since it has such a wide installed base. Attackers can try to insert their own backdoors into a system, for example, using the CMS as an infection vector.

Why Joomla?

“The attackers are doing an object injection via the HTTP user agent that leads to a full remote command execution,” explained Daniel Cid, founder and CTO of Sucuri, on the company’s blog.

The user agent string includes the browser type and version and the computer’s operating system and version. The flaw was caused by a lack of proper filtering when saving browser session values into the database.

In response to the discovery, Joomla issued a patch, V3.4.6, on Dec. 14 that corrected the problem for supported versions of the software. There was also a hotfix issued for the versions of Joomla that had reached their end-of-life phase, namely versions 1.5 and 2.5.

Any organization that uses Joomla will want to patch quickly since cybercriminals are moving fast to exploit any security holes. Cid said that as of Dec. 14, “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.”

Checking Security Posture

To indicate if you have suffered an attack, look for these three IP addresses: 74.3.170.33, 146.0.72.83 and 194.28.174.106. Sucuri found that these were the IPs that generated hundreds of exploitation requests before the patches and hotfixes were developed.

Sucuri also said that users can check if their websites have actually been compromised by searching the logs for “JDatabaseDriverMysqli” or “O:” in the User Agent. That will detect if the backdoor code has been injected.

“That’s a backdoor that executes any PHP code passed by the POST variable 111,” Cid told Threatpost. He added that Sucuri had released a technical analysis of the flaw for security experts looking to learn more about the vulnerability.

This is the second similar incident where a vulnerability was disclosed and quickly patched in Joomla. In October, cybercriminals started exploiting a SQL injection vulnerability just hours after its details were disclosed. At the time, Sucuri detected attack attempts against all the websites on its network, many of which came from the Tor anonymous network.