From the upstream advisory [1]:

Vulnerability Details
=====================

Class:       Cross-Site Scripting
Versions:    2.4 to 3.4.11, 3.5.1 to 3.6.5, 3.7.1 to 4.0.1,
             4.1.1 to 4.1.2
Fixed In:    3.4.12, 3.6.6, 4.0.2, 4.1.3
Description: Bugzilla uses an alternate host for attachments when
             viewing them in raw format to prevent cross-site scripting
             attacks. This alternate host is now also used when viewing
             patches in "Raw Unified" mode because Internet Explorer 8
             and older, and Safari before 5.0.6 do content sniffing,
             which could lead to the execution of malicious code.
References:  https://bugzilla.mozilla.org/show_bug.cgi?id=637981
CVE Number:  CVE-2011-2379

Class:       Information Leak
Versions:    2.23.3 to 3.4.11, 3.5.1 to 3.6.5, 3.7.1 to 4.0.1,
             4.1.1 to 4.1.2
Fixed In:    3.4.12, 3.6.6, 4.0.2, 4.1.3
Description: Normally, a group name is confidential and is only visible
             to members of the group, and to non-members if the group
             is used in bugs. By crafting the URL when creating or
             editing a bug, it was possible to guess if a group existed
             or not, even for groups which weren't used in bugs and so
             which were supposed to remain confidential.
             Moreover, in Bugzilla 4.1.1 and 4.1.2, custom searches also
             let you determine if a group exists or not, even for groups
             which should remain confidential.
References:  https://bugzilla.mozilla.org/show_bug.cgi?id=653477
             https://bugzilla.mozilla.org/show_bug.cgi?id=674497
CVE Number:  CVE-2011-2380, CVE-2011-2979

Class:       Email Header Injection
Versions:    2.17.1 to 3.4.11, 3.5.1 to 3.6.5, 3.7.1 to 4.0.1,
             4.1.1 to 4.1.2
Fixed In:    3.4.12, 3.6.6, 4.0.2, 4.1.3
Description: Bugzilla mostly sends two types of email notifications:
             bugmails and flagmails. A bugmail is the standard email
             users get when a change is made to a bug. A flagmail is
             only sent to the requestee or requester of a flag. For
             flagmails only, attachment descriptions with a newline
             in them could lead to the injection of crafted headers in
             email notifications when an attachment flag is edited.
             Other users only receiving a bugmail are not affected.
References:  https://bugzilla.mozilla.org/show_bug.cgi?id=657158
CVE Number:  CVE-2011-2381

Class:       Unnotified Account Change
Versions:    2.16rc1 to 3.4.11, 3.5.1 to 3.6.5, 3.7.1 to 4.0.1,
             4.1.1 to 4.1.2
Fixed In:    3.4.12, 3.6.6, 4.0.2, 4.1.3
Description: When a user changes his email address, Bugzilla trusts
             a user-modifiable field for obtaining the current e-mail
             address to send a confirmation message to. If an attacker
             has access to the session of another user (for example,
             if that user left their browser window open in a public
             place), the attacker could alter this field to cause
             the email-change notification to go to their own address.
             This means that the user would not be notified that his
             account had its email address changed by the attacker.
References:  https://bugzilla.mozilla.org/show_bug.cgi?id=670868
CVE Number:  CVE-2011-2978

Class:       Local Information Disclosure
Versions:    3.6 to 3.6.5, 3.7.1 to 4.0.1, 4.1.1 to 4.1.2
Fixed In:    3.6.6, 4.0.2, 4.1.3
Description: Temporary files for uploaded attachments are not deleted
             on Windows. A user with local access to the server could
             read these attachments even if he wouldn't normally be
             allowed to view them from Bugzilla.
References:  https://bugzilla.mozilla.org/show_bug.cgi?id=660502
CVE Number:  CVE-2011-2977

Class:       Cross-Site Scripting
Versions:    2.16rc1 to 3.4.11
Fixed In:    3.4.12
Description: If a BUGLIST cookie is compromised (which is not possible
             except via a vulnerability outside of Bugzilla), it can be
             used to inject HTML code when viewing a bug report, leading
             to a cross-site scripting attack.
             Bugzilla 3.5.1 and above are not affected by this issue.
References:  https://bugzilla.mozilla.org/show_bug.cgi?id=660053
CVE Number:  CVE-2011-2976

[1] http://www.bugzilla.org/security/3.4.11/

Fedora has 3.6.6 currently in testing, but EPEL6 has 3.4.11 in testing and EPEL4/5 are shipping old versions (3.2.4); they should all be updated to 3.4.12 to correct these flaws.