The ACL handling in rsyslog 3.12.1 to 3.20.0, 4.1.0, and 4.1.1 does not follow $AllowedSender directive, which allows remote attackers to bypass intended access restrictions and spoof log messages or create a large number of spurious messages.
https://exchange.xforce.ibmcloud.com/vulnerabilities/47080
http://www.securityfocus.com/bid/32630
http://www.rsyslog.com/Topic4.phtml
http://www.rsyslog.com/Article327.phtml