All Bugzilla hosting customers have been upgraded to Bugzilla 4.0.4.
You can read more about the release at the Bugzilla site.
A number of changes were released to address this http://www.bugzilla.org/security/3.4.13/:
- When a user creates a new account, Bugzilla doesn't correctly reject email addresses containing non-ASCII characters, which could be used to impersonate another user account. Such email addresses could look visually identical to other valid email addresses, and an attacker could try to confuse other users and be added to bugs he shouldn't have access to.
- Due to a lack of validation of the Content-Type header when making POST requests to jsonrpc.cgi, a possible CSRF vulnerability was discovered. If a user visits an HTML page with some malicious JS code in it, an attacker could make changes to a remote Bugzilla installation on behalf of the victim's account by using the JSON-RPC API. The user would have had to be already logged in to the target site for the vulnerability to work.