Redirection of thumb.php was introduced in rMW82a8e07935. It is plainly broken for MediaWiki installations lacking a 404 thumb handler, since it redirects from thumb.php (which is meant to render the image) directly to the nonexistent thumbnail URL.

Even for installations that do have a 404 handler, it is presumably unexpected that thumb.php could redirect to something other than thumb.php. It seems to be an unintended consequence of sharing code with the 404 handler.

Version: 1.23.0
Severity: normal