When "dict" passdb and userdb were used for user authentication, the username sent by the IMAP/POP3 client was sent through var_expand() to perform %variable expansion. Sending specially crafted %variable fields could result in excessive memory usage causing the process to crash (and restart), or excessive CPU usage causing all authentications to hang.
This issue was introduced by:
Vulnerable versions: 2.2.26 - 2.2.28
Name: the Dovecot project
According to analysis conducted by Red Hat and Debian, and acknowledged by the Dovecot project, versions prior to 2.2.26 were not affected by this issue.
Versions of dovecot shipped in Red Hat Enterprise Linux 5, 6 and 7 are not affected by this vulnerability.
Created dovecot tracking bugs for this issue:
Affects: fedora-all [bug 1441457]