Vulnerabilities affecting a popular WordPress plugin are being abused by cybercriminals to hijack websites and redirect their visitors to a page set up to serve malware, researchers at Sucuri reported on Monday.
The security firm said more than 100,000 WordPress websites have been compromised. A malicious script planted on the targeted sites loads a JavaScript malware hosted on the SoakSoak.ru domain.
According to researchers, the attackers are exploiting a vulnerability in Slider Revolution, a premium plugin that allows users to easily create responsive sliders. The flaw in question, a local file inclusion (LFI) affecting version 4.1.4 and earlier, was silently patched by the developer, ThemePunch, back in February. In September, Sucuri discovered that the bug, which allows a remote attacker to download any file from affected servers, had been exploited in the wild.
In the latest campaign, the attackers first scan WordPress websites to see if they have Slider Revolution installed. If the plugin is found, the LFI vulnerability is exploited in order to download the “wp-config.php” file, which contains important configuration data that can be leveraged by the attacker to compromise the website.
In the second phase of the attack, a different Slider Revolution vulnerability is exploited in order to upload a malicious theme to the targeted website. First, the attackers upload the Filesman backdoor, which gives them full access, and then they inject a second backdoor, which modifies the “swfobject.js” file so that the site’s visitors are redirected to soaksoak.ru.
“This campaign is also making use of a number of new backdoor payloads, some are being injected into images to further assist evasion and others are being used to inject new administrator users into the WordPress installs, giving them even more control long term,” Daniel Cid, founder and CTO of Sucuri, noted in a blog post. “Some users are clearing infections and getting reinfected within minutes and the reason is because of the complex nature of the payloads and improper cleaning efforts.”
Google has already blacklisted more than 11,000 websites affected by the SoakSoak malware. Google’s Safe Browsing report for soaksoak.ru shows that the domain has functioned as an intermediary for the infection of 27 sites, and it has infected over 16,000 domains.
Slider Revolution has been sold over 42,000 times on the snippets and scripts marketplace CodeCanyon. The bigger issue however is that the plugin is wrapped into a large number of WordPress theme packages, which is why many website owners are not even aware of the fact that Slider Revolution is installed.
WordPress website administrators can use Sucuri’s free SiteCheck scanner to see if they are affected by this attack.
This isn’t the first time a vulnerability in a WordPress plugin is exploited to hijack tens of thousands of websites. Back in July, Sucuri reported that cybercriminals had compromised roughly 50,000 sites by exploiting a flaw in the MailPoet plugin.