David Dede from Sucuri security research company has claimed that any WordPress theme or plugin that runs a genericons package is at risk. Dede adds that the one of the default themes for WordPress, TwentyFifteen, as well as the JetPack plugin, use the genericons icon fonts package.
The vulnerability can allow attackers to hack into any WordPress website using the default theme and plugin if the administrator accidentally clicks on a malicious link. The genericons package comes with an insecure file that makes the site open to cross-site scripting vulnerability.
The firm on Thursday released version 4.2.2 update which is basically a security and maintenance release targeted to fix the vulnerability. The latest release addresses two security issues including updated genericons used in default themes and plugins that scan the WordPress content directory for the affected (and "nonessential") example.html file and removes it.
Dede of Sucuri tried to demystify the vulnerability and explains, "The XSS vulnerability is very simple to exploit and happens at the Document Object Model (DOM) level. DOM-Based XSS is an XSS attack wherein the attack payload is executed as a result of modifying the Document Object Model (DOM) "environment" in the victim's browser used by the original client side script, so that the client side code runs in an "unexpected" manner. That is, the page itself (the HTTP response that is) does not change, but the client side code contained in the page executes differently due to the malicious modifications that have occurred in the DOM environment."
The security firm has also listed few hosts that have also patched the issue recently including GoDaddy, HostPapa, DreamHost, ClickHost, Site5, and SiteGround among others.