WordPress.org has released WordPress version 3.1.1 a maintenance and security update to WordPress 3.1.
WordPress 3.1.1 fixes almost thirty issues in 3.1, including:
Some security hardening to media uploads
Performance improvements
Fixes for IIS6 support
Fixes for taxonomy and PATHINFO (/index.php/) permalinks
Fixes for various query and taxonomy edge cases that caused some plugin compatibility issues
“Version 3.1.1 also addresses three security issues discovered by WordPress core developers Jon Cave and Peter Westwood, of our security team. The first hardens CSRF prevention in the media uploader. The second avoids a PHP crash in certain environments when handling devilishly devised links in comments, and the third addresses an XSS flaw.”
More: http://wordpress.org/news/2011/04/wordpress-3-1-1/
WordPress Trac: http://core.trac.wordpress.org/changeset?new=17595@branches/3.1&old=17487@branches/3.1
