What is referred to as a "high-risk XSS" vulnerability in your article is actually very low risk. It was a reflected cross-site scripting (XSS) vulnerability, which isn't something that hackers try to exploit at all on the average website and even in a targeted attack an attacker would have to bypass protection provided by major web browsers other than Firefox. The claim that it was high-risk came from a company behind a competing caching plugin, which wasn't clearly noted in the linked source.

Our experience has been that severity based ratings of WordPress plugin vulnerabilities often significantly overstate the risk and we have found that it is better to express the risk based on the likelihood of exploitation since that provides a better understanding of the danger presented by the vulnerability.