The unison command in scponly before 4.0 does not properly restrict programs that can be run, which could allow remote authenticated users to bypass intended access restrictions and execute arbitrary programs via the (1) -rshcmd or (2) -sshcmd flags.
https://exchange.xforce.ibmcloud.com/vulnerabilities/18362
https://euvd.enisa.europa.eu/vulnerability/EUVD-2004-1160
http://www.sublimation.org/scponly/#relnotes
http://www.securityfocus.com/bid/11791
http://www.gentoo.org/security/en/glsa/glsa-200412-01.xml