Millions of WordPress sites at risk of hijack after zero-day released

WordPress issued a security update shortly after the news broke over the weekend.
Written by Zack Whittaker, Contributor
WordPress vulnerability affects millions of sites
(Image: Ingvar Bjork/stock image)

A new proof-of-concept code that could hijack millions of WordPress websites has been released.

The cross-site scripting (XSS) vulnerability could allow a malicious attacker to take over an entire server running the blogging platform by changing passwords and creating new accounts.

The vulnerability works by injecting code into the comments section of the site, and then adding a massive amount of text -- more than 64 kilobytes worth. By default, WordPress doesn't publish a commenting user's first post until it has been approved. An attacker can thus fool the administrator with a benign first comment, which would enable further malicious comments from that user to be automatically approved.

WordPress versions 3.9.3, 4.1.1, 4.1.2, and the latest version 4.2 are affected.

Finland-based Jouko Pynnonen, who works for security firm Klikki Oy, detailed the proof-of-concept code. It follows in the footsteps of a similar flaw discovered in recent weeks.

Pynnonen said he disclosed the vulnerability because WordPress "refused all communication attempts" he made since November 2014.

On Monday, the company issued a "critical" security update, WordPress 4.2.1, addressing the flaw. (WordPress did not return an email for comment later in the day.)

Editorial standards