imudp in rsyslog 4.x before 4.1.2, 3.21 before 3.21.9 beta, and 3.20 before 3.20.2 generates a message even when it is sent by an unauthorized sender, which allows remote attackers to cause a denial of service (disk consumption) via a large number of spurious messages.

More... (http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2008-5618)