A recently patched WordPress vulnerability has been used to deface roughly 1.5 million web pages and experts have also started seeing attempts to exploit the flaw for remote code execution.
The flaw in question was patched on January 26 with the release of WordPress 4.7.2, but its existence was only disclosed one week later in an effort to give users enough time to update their installations.
The security hole affects the REST API and it has been described as a privilege escalation and content injection vulnerability. It allows attackers to modify the content of any post or page, and it can also be exploited for arbitrary PHP code execution.
Despite WordPress developers giving users a week to update their installations and working with service providers to block exploitation attempts, many websites that don’t have automatic updating enabled are still vulnerable to attacks.
A majority of the attacks spotted so far are part of defacement campaigns conducted by script kiddies looking to boost their online reputation. In the first days after exploits were made public, Sucuri researchers observed four campaigns in which more than 60,000 pages had been defaced.
The number has increased significantly and WordPress security firm WordFence reported on Thursday that it had spotted roughly 1.5 million defaced pages in attacks carried out by 20 different hackers.
WordFence pointed out that none of these hackers had managed to deface too many websites at once before the disclosure of this WordPress vulnerability. Several exploits have been used in the recent attacks and, in some cases, the attackers had found ways to bypass the rules deployed by firewall vendors.
While defacement attacks are not easy to monetize, researchers at Sucuri have started seeing other types of operations involving the REST API flaw.
The vulnerability cannot be directly used for code execution. However, WordPress plugins that allow users to insert PHP code directly into posts can be combined with the flaw to achieve this. Sucuri has seen exploitation attempts against websites that have plugins such as Insert PHP and Exec-PHP, both of which have over 100,000 active installs.
“Defacements don’t offer economic returns, so that will likely die soon,” explained Daniel Cid, founder and CTO of Sucuri. “What will remain are attempts to execute commands (RCE) as it gives the attackers full control of a site – and offers multiple ways to monetize – and SPAM SEO / affiliate link / ad injections. We are starting to see them being attempted on a few sites, and that will likely be the direction this vulnerability will be misused in the coming days, weeks and possibly months.”
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