Cisco Unified IP 9900 phones with firmware 9.4(.1) and earlier use weak permissions for unspecified files, which allows local users to cause a denial of service (persistent hang or reboot) by writing to a phone's filesystem, aka Bug ID CSCup90474.
https://exchange.xforce.ibmcloud.com/vulnerabilities/100619
http://www.securityfocus.com/bid/72484
http://tools.cisco.com/security/center/viewAlert.x?alertId=37345
http://tools.cisco.com/security/center/content/CiscoSecurityNotice/CVE-2015-0603