iCal 2.1 Patch 2 installs many files with world-writeable permissions, which allows local users to modify the iCal configuration and execute arbitrary commands by replacing the iplncal.sh program with a Trojan horse.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5756
https://euvd.enisa.europa.eu/vulnerability/EUVD-2000-1058
http://www.securityfocus.com/bid/1768
http://www.atstake.com/research/advisories/2000/a100900-1.txt