Incorrect files permissions in version 3.0.0
From Joomla! Documentation
The Linux file permissions for version 3.0.0 are incorrectly set in the download archive files. The correct file permissions should be read/write only for the owner and read-only for group and other. In the 3.0.0 archives, this is incorrectly set as read-write for the owner and group members.
For example, if you do the command
ls -l at the Joomla root folder, you will see:
-rw-rw-r-- ..... joomla.xml
Instead you should see:
-rw-r--r-- ..... joomla.xml.
You can fix this from the Linux command line by navigating to the root folder of Joomla and typing this command:
chmod -R g-w *
Note: This will be corrected automatically when you update to version 3.0.1.