The check_secret function in authenticate.c in rsync 3.1.0 and earlier allows remote attackers to cause a denial of service (infinite loop and CPU consumption) via a user name which does not exist in the secrets file.
https://git.samba.org/?p=rsync.git%3Ba=commit%3Bh=0dedfbce2c1b851684ba658861fe9d620636c56a
https://bugzilla.samba.org/show_bug.cgi?id=10551
https://bugs.launchpad.net/ubuntu/+source/rsync/+bug/1307230
http://www.ubuntu.com/usn/USN-2171-1
http://www.openwall.com/lists/oss-security/2014/04/15/1
http://www.openwall.com/lists/oss-security/2014/04/14/5
http://www.mandriva.com/security/advisories?name=MDVSA-2015:131
http://secunia.com/advisories/57948
http://lists.opensuse.org/opensuse-updates/2014-05/msg00006.html
http://lists.fedoraproject.org/pipermail/package-announce/2014-April/131910.html