WordPress have released an update (3.0.4), dubbed “the most important security release of the year”, that patches a core security bug in the HTML sanitation library (KSES). KSES is responsible for filtering user input and, as such, is used to protect WordPress sites from attacks such as Cross-Site Scripting (XSS). XSS vulnerabilities were discovered, however the details of these are not available (see below).
They rate this release “critical”, and so it’s recommended that all WordPress sites update as soon as possible. The full changeset for the 3.0.4 update is here. Security researchers are invited to review these changes to ensure the vulnerabilities have been fully fixed. Spread the news if you have any friends with a WordPress blog!
[Updated] One stored XSS exploit for 3.0.3 is available here.