APC UPS daemon, apcupsd, saves its process ID in a world-writable file, which allows local users to kill an arbitrary process by specifying the target process ID in the apcupsd.pid file.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5654
http://www.securityfocus.com/bid/2070
http://www.linux-mandrake.com/en/security/MDKSA-2000-077.php3