You have to set the following CHMOD permissions to your files :
Wp-config.php : 640
.htaccess : 644
Sitemap.xml : 666
Wp-content : 755
All other files : 644
If you get a http error 500 after an update of WordPress, that means that there is something wrong with your CHMOD permissions or that your htaccess file might be corrupted.
That’s why it is important to do a backup prior to a full update of the WordPress cms.