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Critical WordPress XSS Flaw Left 86% of Sites at Risk

A whopping 86% of WordPress sites may have been vulnerable to a newly discovered, critical cross-site scripting (XSS) flaw which went unreported for over four years, according to security researchers.

Finnish firm Klikki Oy found the vulnerability in version 3.0 of the popular blogging software, which was released in 2010. Although version 4 is not affected by the flaw, most users – tens of millions in fact – are still on the older software platform.

The firm explained more in a blog post:

“An attacker could exploit the vulnerability by entering carefully crafted comments, containing program code, on WordPress blog posts and pages. Under default settings comments can be entered by anyone without authentication (login).

Program code injected in comments would be inadvertently executed in the blog administrator's web browser when they view the comment. The rogue code could then perform administrative operations by covertly taking over the administrator account.”

Such “administrative operations” could include taking over the site by creating a new admin account and changing the current account password, then executing malicious PHP code on the server.

Although the flaw could be the worst for the blogging giant in five years, Klikki Oy said it had been working with the firm since 26 September and last week WordPress released official patches to deal with the issue.

These come in the form of automatic updates, so most users should be protected by default.

More technical details from Klikki Oy are available here.

Cross-site scripting flaws are some of the most prevalent and dangerous around, according to security vendor High-Tech Bridge. The firm claimed that XSS accounted for the majority of the 169 flaws it has published in recent years.

"SQL injection vulnerabilities are becoming more and more rare, as well as other high and critical risk vulnerabilities. They are complex to detect and quite often require a lot of time to exploit,” argued HTB CEO Ilia Kolochenko.

“At the same time almost nobody cares about ‘medium-risk’ XSS vulnerabilities, leaving their websites vulnerable. Obviously, hackers benefit from such negligence and use XSS vulnerabilities to achieve their goals.”

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