Tavis Ormandy reported a common DNS misconfiguration that can result in a minor security issue with web
"It's a common and sensible practice to install records of the form "localhost. IN A 127.0.0.1" into nameserver configurations, bizarrely however, administrators often mistakenly drop the trailing dot, introducing an interesting variation of Cross-Site Scripting (XSS) I call Same-Site Scripting. The missing dot indicates that the record is not fully qualified, and thus queries of the form "localhost.example.com" are resolved. While superficially this may appear to be harmless, it does in fact allow an attacker to cheat the RFC2109 (HTTP State Management Mechanism) same origin restrictions, and therefore hijack state management data."
It is advised that non-FQ localhost entries be removed from nameserver configurations for domains that host websites that rely on HTTP state management.
Common dns misconfiguration can lead to "same site" scripting