Last modified: 2010-05-15 15:33:54 UTC
It's possible to redirect to a google cache: #REDIRECT [[cache:www.google.com]] and, of course, to goatse and whatnot, thus this feature (intentional or otherwise) is a magnet for vandalism.
The real bug here is that redirects to "external" interwikis should not be possible - such interwikis are just shorthand for URLs, and since you can't redirect to URLs, why should interwikis be any difference. In contrast, "internal" interwiki links - e.g. between the Wikimedia prjoects, such as from Wikipedia to Wiktionary - should be made so that they "know" where they've been redirected from (if it's an internal interwiki, we know the target's a MediaWiki install). See also bug 850 and bug 999. As a workaround, perhaps the "Cache:" prefix should be taken out of the interwiki map, and in general the list of prefixes be reviewed taking the ability to redirect into consideration.
Since a while back, only internal interwikis may be redirected to.
