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RE: SQL Injection or XML
From: gcb33 () dial pipex com
Date: Wed, 9 Jun 2004 12:38:34 +0100


My quick suggestion or experience

Most vendors that I used are now not sucseptable to SQL injection even if their
is no filtering or character injection in any form, they do use XML schemas to
talk from web server aspx pages to the app server we also use XML to the
back-end or middleware systems for on-line enquires for cash or account balance
as in a internet banking application

With experiense I have found that when you have multi-lingual web site
especially if it uses non european characters they would hard code the values to
reject on , not ideal but then better than nothing non the less. so reject on if
allowed it is harder to setup but more secure. as in this case mentioned next 

I found one case is if you have a mixture of vendor products that a certain
characters that are not exploitable would appear not to work will effect another
like a this setup web server and app server is Micrsoft with a database is
either DB2 or Oracle that the high order ANSI code 145 or 146 would be treated
the sames as ' so even if you think that you have blocked the normal ASCII ; or
' characters would still be susceptable to SQL injection

A key question or point for design of security components if when the component
or components fails under extreme conditions how is the application going to
handle this condition , as in pre-production or UAT enviroments you cannot
simulate 100,000 users logged into at once with multiple calls to systems async
logical required  components do fail in productions for no apparent resone and
would giver eranous errors or could allow for certain validation sequences to fail.

And the other two security areas i have seen which is always over looked is
session management of the site... with clustered enviroments always without a
doubt will work given enough time on nearly 60-70% of vendors products in the
wild. SQL injections is mostly resolved for enterprise products but now with XML
with the new 'XML injection' as i call is the next thing and found it on one
vendor product due to the order of the validation componets before calling the
XML listerner middle of last year

Their are excellent materials writtern by microsoft press the blue books on
pattern matching and application design plus the black book on security
programming that has been mentioned that as been invaluable in re-writtern are
applications allowing the developersand system architect to design to a very
granually componets for security. We are also using 'Biztalk product' to allow
for easy B2B messaging translations on the XML schema for dual direction
messaging formats. so SQL yes needs to be addressed but also XML as most systems
are now been designed for XML messaging to core banking middle-ware or hosting
systems with straight through processing so the SQL is a risk but XML is more
damaging if it succeeds.

Security Developer or Consultant and Pentester for Banks

Quoting Michael Howard <mikehow () microsoft com>:

The list, while useful, is very US-centric. You may want to point that
out in the XML schema - perhaps have a country code attribute or

I often look at RegExLib for ideas - including non-US constructs:

[Writing Secure Code 2nd Edition]
[Protect Your PC] http://www.microsoft.com/protect
[Blog] http://blogs.msdn.com/michael_howard
[Annual Security Training]

-----Original Message-----
From: Jeff Williams [mailto:jeff.williams () aspectsecurity com] 
Sent: Sunday, June 06, 2004 9:19 PM
To: tcroc () pasture com; stevenr () mastek com
Cc: coley () mitre org; webappsec () securityfocus com
Subject: Re: SQL Injection

Here's a little list of regex's that I put together for an article about
to build an HTTP Request Validation Engine (see
http://www.aspectsecurity.com/stinger). If anyone knows of a more
list with some better documentation, I think it could be pretty helpful

Architecturally, I think there's a strong case for a centralized
engine, as opposed to putting a regex in front of every place you use
something from the HTTP request.

Here's a few quick questions to see if you're really validating well:
 - Is your validation scheme mandatory (developer doesn't have to
to do it)
 - Do you canonicalize before validating?
 - Are you validating URL params, cookies, and other headers -- or just
 - Do you catch extra, missing, and duplicate parameters, headers,
 - If you detect a problem, what are your options (ignore, sanitize,
continue, fatal, log, notify)?
 - Can you detect an attack based on repeated failed input validation?
 - Is what you log different than what you show the user?

Wait -- here are the best ones:
 - Do your requirements specify all the stuff above?
 - Do your requirements or detailed design docs specify all the

Input validation shouldn't just be left to 'best practice' or whatever
individual developers want to do.  It takes some real design thinking to
it right for an enterprise application.


Jeff Williams
Aspect Security, Inc.

----- Original Message ----- 
From: "The Crocodile" <tcroc () pasture com>
To: <stevenr () mastek com>
Cc: <coley () mitre org>; <webappsec () securityfocus com>
Sent: Saturday, June 05, 2004 9:19 AM
Subject: RE: SQL Injection

Blindly encoding characters may still cause errors and issues if that
input is utilized prior to encoding, or if the input in encoded form
contains characters that will cause errors. You should always validate
the input regardless and then encode the output prior to presenting it
back to the end user.

A better question is are there any publically available "whitelist"
based libraries that are easy to use for input validation? In what
langauages are these libraries available? Is there a compiled list of
these libraries somewhere that I am unaware of?

It would be great to have an extensible regex style whitelist library
available where a simple function(s) can be called with the line of
input and the whitelist regex and a 1 or 0 are returned. (This has
oversimplified for the sake of the post).

I did a brief google search "input validation library", but didn't see
anything at first glance.

Comments welcome.


--The Crocodile

On Sat, 2004-06-05 at 02:17, stevenr () mastek com wrote:

When I had mentioned whitelists in my post, I meant whitelists as
forth by Crocodile. Its about creating rules about what characters
be allowed and rejecting (or encoding) the rest. Another approach
I think may help (as mentioned by Crocodile) is blindly encoding all
input and then saving it in the db (or showing it on the page). This
not always be right, specially if there are other tools/systems
read the data but are unable to decode it back to original form.

BTW, any opinions on if I just encode all input without checking for
characters? Say converting all <script> to &lt;script&gt; Can anyone
still do XSS or SQL Injection in that case?

Steven Rebello

-----Original Message-----
From: The Crocodile [mailto:tcroc () pasture com]
Sent: Friday, June 04, 2004 5:55 PM
To: Steven M. Christey
Cc: webappsec () securityfocus com
Subject: Re: SQL Injection

I think I'm confused about your use of the term "whitelist" in the
scenario below. White lists IMHO aren't going to be vulnerability
specific at all. They are going to be specific to the particular
parameter in question. I don't see how you would have differing
"whitelists" for XSS and for SQL Injection.

A white list is specifically what is going to be allowed for a
particular parameter. For example a phone number in the US might
1234567890()- and that's it. White listing the particular input
field to
allow only those characters (and escape them if neccesary) should
both XSS and SQL injection attack characters. Encoding the output
presented to the user is an additional step that can be done to
check for display type attacks (again XSS).

Maybe I misunderstood your post, but I just wanted to make sure
subtle differences were clear to the list.


--The Crocodile

And yes I know "whitelisting" won't catch input data that is valid
additional business logic should be catching. IE. Access control
violations. That is a different thread all together.

On Thu, 2004-06-03 at 20:35, Steven M. Christey wrote:
The best way would be creating a white list, allowing only
characters and rejecting everything else. Saves you headaches in
long run. Use Regexs for this.

While white lists are far better than black lists, the correct
list" will vary depending on which type of vulnerability you are
protecting against.  For example, restricting inputs to
spaces, and hyphens will still open you up to certain argument
injection vulnerabilities.  So, you may need to apply different
lists to the data, depending on where (and how) the data is being
used, and which types of vulnerabilities may be present at that
You may want to use a "SQL injection" white list on data input,
an "XSS white list" on data output (though "XSS white list" is
an oxymoron these days, with all the custom browser behaviors).

It would be interesting to know if anybody's tried to implement
"context-sensitive taint checks" that know which filters have been
applied to data elements, and when.

- Steve

"Making a valuable difference"
Mastek in NASSCOM's 'India Top 20' Software Service Exporters List.
In the US, we're called MAJESCO

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