Active malware campaign uses thousands of WordPress sites to infect visitors

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15-day-old campaign has spiked in past 48 hours, with >5,000 new infections daily.

Attackers have hijacked thousands of websites running the WordPress content management system and are using them to infect unsuspecting visitors with potent malware exploits, researchers said Thursday.

The campaign began 15 days ago, but over the past 48 hours the number of compromised sites has spiked, from about 1,000 per day on Tuesday to close to 6,000 on Thursday, Daniel Cid, CTO of security firm Sucuri, said in a blog post. The hijacked sites are being used to redirect visitors to a server hosting attack code made available through the Nuclear exploit kit, which is sold on the black market. The server tries a variety of different exploits depending on the operating system and available apps used by the visitor.

Active malware campaign uses thousands of WordPress sites to infect visitors

“If you think about it, the compromised websites are just means for the criminals to get access to as many endpoint desktops as they can,” Cid wrote. “What’s the easiest way to reach out to endpoints? Websites, of course.”

On Thursday, Sucuri detected thousands of compromised sites, 95 percent of which are running on WordPress. Company researchers have not yet determined how the sites are being hacked, but they suspect it involves vulnerabilities in WordPress plugins. Already, 17 percent of the hacked sites have been blacklisted by a Google service that warns users before they visit booby-trapped properties. Interestingly, Cid added, the attackers have managed to compromise security provider Coverity and are using it as part of the malicious redirection mechanism. The image above shows the sequence of events as viewed from the network level using a debugging tool.

Sucuri has dubbed the campaign “VisitorTracker,” because one of the function names used in a malicious javascript file is visitorTracker_isMob(). Cid didn’t identify any of the compromised sites. Administrators can use this Sucuri scanning tool to check if their site is affected by this ongoing campaign.