A vulnerability in the web-based management interface of Session Initiation Protocol (SIP) Software for Cisco IP Phone 7800 Series and Cisco IP Phone 8800 Series could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition or execute arbitrary code. The vulnerability exists because the software improperly validates user-supplied input during user authentication. An attacker could exploit this vulnerability by connecting to an affected device using HTTP and supplying malicious user credentials. A successful exploit could allow the attacker to trigger a reload of an affected device, resulting in a DoS condition, or to execute arbitrary code with the privileges of the app user. Cisco fixed this vulnerability in the following SIP Software releases: 10.3(1)SR5 and later for Cisco Unified IP Conference Phone 8831; 11.0(4)SR3 and later for Cisco Wireless IP Phone 8821 and 8821-EX; and 12.5(1)SR1 and later for the rest of the Cisco IP Phone 7800 Series and 8800 Series.