Sun ONE (aka iPlanet) Web Server 6 on Windows, when DNS resolution is enabled for client IP addresses, uses a logging format that does not identify whether a dotted quad represents an unresolved IP address, which allows remote attackers to spoof IP addresses via crafted DNS responses containing numerical top-level domains, as demonstrated by a forged 123.123.123.123 domain name, related to an "Inverse Lookup Log Corruption (ILLC)" issue.