Vulnerability Instance

Security researcher Masato Kinugawa discovered that if a web
page is missing character set encoding information it can inherit character
encodings across navigations into another domain from an earlier site. Only
same-origin inheritance is allowed according to the HTML5 specification. This
issue allows an attacker to add content that will be interpreted one way on the
victim site, but which may then behave differently, evading cross-site scripting
(XSS) filtering, when forced into an unexpected character set. Web site authors
should always explicitly declare a character encoding to avoid similar issues.
In general these flaws cannot be exploited through email in the
Thunderbird and Seamonkey products because scripting is disabled, but are
potentially a risk in browser or browser-like contexts.