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Re: RFP2K01 - "How I hacked Packetstorm" (wwwthreads advisory)
From: ross () MATHFORUM COM (Aaron Ross)
Date: Tue, 8 Feb 2000 08:50:10 -0500


 Despite MySQL's implicit conversion, many RDBMS do _not_ allow strings around
numeric values:

 With Sybase 11.9.2 e.g.

1> create table strnum (
2>  col1 int
3> )
4> go
1> insert into strnum values ('1')
2> go
Msg 257, Level 16, State 1
, Line 1
Implicit conversion from datatype 'VARCHAR' to 'INT' is not allowed.  Use the
CONVERT function to run this query.

 Aaron

Hi,

-----Original Message-----
From: Bugtraq List [mailto:BUGTRAQ () SECURITYFOCUS COM]On Behalf Of rain
forest puppy
Sent: 03. veebruar 2000. A. 18:33
To: BUGTRAQ () SECURITYFOCUS COM
Subject: RFP2K01 - "How I hacked Packetstorm" (wwwthreads advisory)

a nice analysis otherwise, but this caught my eye:

You see, there are different field types.  You can have
strings, boolean
values, various numeric values, etc.  While a string field
needs to be in
the format of field='data', a numeric field doesn't use the '' (i.e.
numeric_field='2' is invalid).  The correct syntax for
numeric fields in
numeric_field=2.  Ah ha!  There's no quotes to deal with, and
you can't
even use quotes anyways.  The correct solution is to make

If you're stating that you cannot enclose your numeric values in single
quotes in SQL query strings, it seems to be incorrect. I'm also using SQL as
my backend, and I've ALWAYS enclosed numbers in single quotes, and it has
always worked.

Besides, when using PHP as front end, it has the nice AddSlashes and
StripSlashes functions, which, according to the manual, "Returns a string
with backslashes before characters that need to be quoted in database
queries etc. These characters are single quote ('), double quote ("),
backslash (\) and NUL (the null byte).", and "Returns a string with
backslashes stripped off. (\' becomes ' and so on.) Double backslashes are
made into a single backslash.". So it's exactly what we need to "disarm" web
queries, and pretty much the same as the $dbh->quote thing (though you later
have to 'decode' the data and strip the backslashes).

I wrote two "wrapper" functions for PHP, which take their input and add or
strip slashes (recursively if needed) on both arrays and normal variables
(never mind the funny names, you can change them if you want, but the idea
should be clear :). I'm sure it could be done more effectively, and in other
languages too, but I'm not much of a code wizard, so let's stick with these
for now.

function paneslash (&$sisend) {
      if (is_array($sisend)) {
              while (list($siskey) = each($sisend)) {
                      paneslash($sisend[$siskey]);
              }
      } else {
              $sisend = addslashes($sisend);
      }
}

function korjaslash (&$sisend) {
      if (is_array($sisend)) {
              while (list($siskey) = each($sisend)) {
                      korjaslash($sisend[$siskey]);
              }
      } else {
              $sisend = stripslashes($sisend);
      }
}

This way, when fetching data from database, you can just say

$my_array=mysql_fetch_array($some_query);
korjaslash($my_array);

and boom, backslashes are stripped (provided there were any). Prior to
inserting/updating data, just go through each variable with
paneslash($varname) and off you go. When performing insert/update, I have
always used the "update blaah set columnname='value'" syntax with single
quotes always surrounding, regardless of the columnname type (integer,
string etc), and it has worked with no trouble.

However, checking numeric data for validity is still a healthy practice,
since it's likely you'll later pass it to functions (like calculations or
something) that assume they're dealing with valid numbers - and when
inserting non-numeric data to columns of numeric type, MySQL seems to
quietly replace it with zero (at least in case of integers).

PHP has a nice set of is_* functions (like is_array, is_int etc), but they
seem to be somewhat broken/misdocumented - when using <input type="text">
and passing the form to PHP script, this variable (before interpreting it
anyhow) is always assumed to be string, even when it only contains valid
numeric data. (the is_array in above functions works fine, though, so
perhaps I've misread something.) Other functions that could be used are the
GetType and SetType in PHP - when a variable is supposed to be numeric, but
contains non-numeric data, GetType reports it to be something else than
integer, and perhaps you can then warn user about this - A.K.A. server-side
validation, which should be a normal, healthy, common sense programming
practice anyway ("NEVER trust the user..."). Moreover, it's more secure than
client-side validation, since one who has malicious intent can always
construct their own form/query and just delete the validating JavaScript or
whatever on the client side.

The PHP/MySQL combination is powerful, elegant, and easy to use (as well as
many other front- and backends). As dynamic page generation is gaining
momentum and discussion forums, user profile maintenance pages etc are
popping up all over the place, I'm sure we'll see many more vulnerabilities
of this type both in custom-written scripts as well as commercial software
(as the WWWThreads example demonstrated). With software that is both easy to
use and rich in features, security concerns are often disregarded - many
entry-level webmasters and script developers are clueless about the above
possibilities. So let's keep our eyes open, and queries safe.

Regards,
Jaanus Kase
Cybernetica (http://www.cyber.ee/)


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