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Re: FW: ban the use and implementation of UTF-7

From: Addison Phillips <addison@yahoo-inc.com>
Date: Tue, 19 Dec 2006 10:51:10 -0800
Message-ID: <4588349E.8080704@yahoo-inc.com>
To: www-international@w3.org
CC: ietf-charsets@iana.org

 >> It seems completely unnecessary given the now ubiquitous use of 8-bit
 >> clean transports and the presence of UTF-8, which IIRC was defined
 >> long after UTF-7.  However, the wider community may be aware of
 >> some reason why browsers should support it, so I'd like to hear
 >> your comments.

The problem, as I see it, is not that the browsers support conversion 
using UTF-7. It is that they auto-detect UTF-7. Since UTF-7 uses plain 
ASCII characters to form escape sequences, it turns out to be trivial to 
fool a browser into detecting UTF-7, causing an XSS security hole.

Some of us have spent more than ample time building anti-UTF-7 code 
(such as judiciously replacing '+' in UTF-7 spoof sequences with 
'&#43;'). It is nutty.

I agree with the basic premise of Roy's that UTF-7 ought to be banned. 
But it would be simpler to remove it from the list of things 
auto-detected by user agents. A page that actually uses UTF-7 really 
REALLY ought to declare that encoding (in which case no security flaw is 
present). Otherwise it should display as mojibake.


Addison Phillips
Globalization Architect -- Yahoo! Inc.

Internationalization is an architecture.
It is not a feature.
Received on Tuesday, 19 December 2006 18:51:36 UTC

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