It was discovered that cyrus-imapd, a highly scalable mail system designed for use in enterprise environments, is not properly parsing mail headers when a client makes use of the IMAP threading feature. As a result, a NULL pointer is dereferenced which crashes the daemon. An attacker can trigger this by sending a mail containing crafted reference headers and access the mail with a client that uses the server threading feature of IMAP.
For the oldstable distribution (lenny), this problem has been fixed in version 2.2.13-14+lenny6.
For the stable distribution (squeeze), this problem has been fixed in version 2.2.13-19+squeeze3.
For the testing (wheezy) and unstable (sid) distributions, this problem has been fixed in cyrus-imapd-2.4 version 2.4.11-1.
We recommend that you upgrade your cyrus-imapd-2.2 packages.