RE: Extended ASCII characters used for injection

The statement from www.w3schools.com simply raises more questions in my mind
than it answers:

1.  What does server-side software such as Apache, IIS, PHP, etc. do if they
receive an HTTP request with a URL that contains a character in the range
0x7F to 0xFF?

2.  Will any of the popular Web browsers ever make an HTTP request with a
URL that contains a character in the range 0x7F to 0xFF?

3.  For that matter, are characters in the range 0x7F and 0xFF invalid in
all HTTP headers?

4.  A related question:  How do various server-side software packages handle
invalid UTF-8 multi-byte sequences in HTTP headers and bodies?

I believe that these questions would be best answered with an extensive test
suite.  Perhaps one already exists.

Richard

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Linden Darling
Sent: Wednesday, October 20, 2010 11:56 PM
To: Nibbler
Cc: [email protected]
Subject: RE: Extended ASCII characters used for injection

Assuming you mean "block these characters AFTER they've been decoded
from legitimate URI characters"...otherwise:

http://www.w3schools.com/TAGS/ref_urlencode.asp

"URLs can only be sent over the Internet using the ASCII character-set.

Since URLs often contains characters outside the ASCII set, the URL has
to be converted. URL encoding converts the URL into a valid ASCII
format.

URL encoding replaces unsafe ASCII characters with "%" followed by two
hexadecimal digits corresponding to the character values in the
ISO-8859-1 character-set."

http://en.wikipedia.org/wiki/Percent-encoding

"Percent-encoding a reserved character involves converting the character
to its corresponding byte value in ASCII and then representing that
value as a pair of hexadecimal digits. The digits, preceded by a percent
sign ("%"), are then used in the URI in place of the reserved character.
(For a non-ASCII character, it is typically converted to its byte
sequence in UTF-8, and then each byte value is represented as above."

In line with Jeff's response below, if some part of the decoded URI is
used within a SQL statement, for instance, then there can be problem
situations such as with Big5 characters that can be used for SQL
Injection purposes.

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Jeff Williams
Sent: Thursday, 21 October 2010 2:32 PM
To: Chris Weber
Cc: Nibbler; <[email protected]>
Subject: Re: Extended ASCII characters used for injection

What platform are you using? It really makes a difference in how Unicode
is handled.

--Jeff



On Oct 20, 2010, at 2:29 AM, "Chris Weber" <[email protected]>
wrote:

> You'd be blocking legitimate usage of many different character
encodings
> including UTF-8 and ISO-8859-1 if you blocked 0x77 - 0xff.  
> 
> -----Original Message-----
> From: [email protected]
[mailto:[email protected]] On
> Behalf Of Nibbler
> Sent: Tuesday, October 19, 2010 6:06 AM
> To: [email protected]
> Subject: Extended ASCII characters used for injection
> 
> Hi list,
> 
> I have a web app and I want to block special characters in URL on the
> web server. Do you know if there is a risk of injection (XSS...) with
> extended ASCII char (%7f-%ff)?
> Is there any reason to block these characters?
> 
> Thanks
> Regards,
> Nib
> 
> 
> 
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