David Zülke wrote:
Am 21.08.2008 um 18:41 schrieb Rasmus Lerdorf:
David Zülke wrote:
Am 21.08.2008 um 18:08 schrieb Rasmus Lerdorf:
David Zülke wrote:
Am 21.08.2008 um 03:34 schrieb William A. Rowe, Jr.:
Stanislav Malyshev wrote:
Hi!
Are there any objections to incorporating bugfix for #43941 (fix for
how json handles invalid UTF-8 sequences) into 5.2? I had some
requests about it, right now it's only in 5.3+.
Is there the alternative of substituting an unmappable character
FFFD in
place of the invalid sequence? This a a reasonable alternative
behavior
for some less stringent cases.
(Yes, the fix is better than the status quo, but just taking this a
step
further).
I agree, that would be quite reasonable and also more consistent with
how UTF-8 works in other apps (browsers etc).
Well, using browsers as the benchmark here is a bad idea. IE is
absolutely braindead about dealing with illegal UTF-8 chars. It will
accept just about any sequence of bytes as a valid UTF-8 char which
causes all sorts of problems.
I was talking about the common representation of an invalid sequence.
That's the question mark sign you usually see in a browser when the
encoding is incorrect.
Yes, but it all comes down to how you do it. Say you have a 3 byte
sequence that starts with 0xE0 (E0 indicates the start of a 3-byte
utf-8 char) but the 3 bytes together don't actually make up a valid
utf-8 char. Id you substitute those 3 bytes with a ? or some other
character you have just created a nasty XSS vector for web apps.
You don't substitute it with "a ? or some other character", you replace
it with U+FFFD (0xEF 0xBF 0xBD in UTF-8). I'd love to hear how that
causes an attack vector.
It doesn't matter what you replace it with. If the byte sequence is:
0xE0 " >
And you replace those bytes with some other byte in this sort of context:
<input type=text name=foo value="0xE0">
<input type=text name=bar value="$data">
Now do your silly replacement:
<input type=text name=foo value="0xEF 0xBF 0xBD
<input type=text name=bar value="$data">
That now means that IE interprets the value attribute of the foo element
as: value="0xEF 0xBF 0xBD <input type=text name=bar value="
And now $data is suddenly outside the quoted value attribute! Oops!
Major XSS. Google Groups and Yahoo were both hit by this last year.
-Rasmus
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