the week of silly PoCs continues: data://

From: Michal Zalewski <>
To: bugtraq <>
Subject: the week of silly PoCs continues: data://

Just another short note... this is a somewhat compelling and entirely
unnecessary phishing opportunity - and a tiny symptom of the mess with
URL handling.

Firefox and Opera allow you to omit MIME type in data: URLs, possibly
put random garbage into that section, and still get a valid HTML
document. This is a natural extension of how the Content-Type header
is handled in HTTP, but probably makes little or no sense here.

With the use of Unicode homographs, you can create fairly believable
URLs especially in Firefox:

The appearance may vary depending on your font selection; see for a sample capture.

If you know the special role of "data:", this won't fool you. But most
browser users don't, even if they grasp the basics of URL syntax to
begin with (of course, that part itself is not true in all too many

PS. It is probably better known that a less convincing variant of this
can be achieved with javascript: URLs in MSIE and some other browsers.


Copyright © 1995-2021 All rights reserved.