cyrus-imapd -- multiple buffer overflow vulnerabilities

The Cyrus IMAP Server ChangeLog states:

Fix possible single byte overflow in mailbox handling
code.
Fix possible single byte overflows in the imapd
annotate extension.
Fix stack buffer overflows in fetchnews (exploitable
by peer news server), backend (exploitable by admin),
and in imapd (exploitable by users though only on
platforms where a filename may be larger than a mailbox
name).

The 2.1.X series are reportedly only affected by the second
issue.
These issues may lead to execution of arbitrary code with
the permissions of the user running the Cyrus IMAP
Server.