Multiple vulnerabilities in SYMDNS.SYS for Symantec Norton Internet Security and Professional 2002 through 2004, Norton Personal Firewall 2002 through 2004, Norton AntiSpam 2004, Client Firewall 5.01 and 5.1.1, and Client Security 1.0 through 2.0 allow remote attackers to cause a denial of service or execute arbitrary code via (1) a manipulated length byte in the first-level decoding routine for NetBIOS Name Service (NBNS) that modifies an index variable and leads to a stack-based buffer overflow, (2) a heap-based corruption problem in an NBNS response that is missing certain RR fields, and (3) a stack-based buffer overflow in the DNS component via a Resource Record (RR) with a long canonical name (CNAME) field composed of many smaller components.