I just upgraded this blog to the latest version of WordPress, and I noticed that I wasn’t able to post. Got 403 Forbidden error message.
Checking mod_security’s log file, I saw these messages:
POST /wp-admin/post.php HTTP/1.1
mod_security-message: Access denied with code 403. Invalid cookie format: Cookie value is missing #1
After googling around, turned out it’s because of a setting in a mod_security.
Basically, you’ll need to replace SecFilterCheckCookieFormat to SecFilterNormalizeCookies in your mod_security config.
After doing this and restarting Apache, I can post again to WordPress.
Hope this helps somebody else with similar problem.