mirror of
https://github.com/EGroupware/egroupware.git
synced 2024-11-18 14:03:19 +01:00
204 lines
7.1 KiB
Plaintext
204 lines
7.1 KiB
Plaintext
kses 0.2.1 README [kses strips evil scripts!]
|
|
=================
|
|
|
|
|
|
* INTRODUCTION *
|
|
|
|
|
|
Welcome to kses - an HTML/XHTML filter written in PHP. It removes all unwanted
|
|
HTML elements and attributes, no matter how malformed HTML input you give it.
|
|
It also does several checks on attribute values. kses can be used to avoid
|
|
Cross-Site Scripting (XSS), Buffer Overflows and Denial of Service attacks,
|
|
among other things.
|
|
|
|
The program is released under the terms of the GNU General Public License. You
|
|
should look into what that means, before using kses in your programs. You can
|
|
find the full text of the license in the file COPYING.
|
|
|
|
|
|
* FEATURES *
|
|
|
|
|
|
Some of kses' current features are:
|
|
|
|
* It will only allow the HTML elements and attributes that it was explicitly
|
|
told to allow.
|
|
|
|
* Element and attribute names are case-insensitive (a href vs A HREF).
|
|
|
|
* It will understand and process whitespace correctly.
|
|
|
|
* Attribute values can be surrounded with quotes, apostrophes or nothing.
|
|
|
|
* It will accept valueless attributes with just names and no values (selected).
|
|
|
|
* It will accept XHTML's closing " /" marks.
|
|
|
|
* Attribute values that are surrounded with nothing will get quotes to avoid
|
|
producing non-W3C conforming HTML
|
|
(<a href=http://sourceforge.net/projects/kses> works but isn't valid HTML).
|
|
|
|
* It handles lots of types of malformed HTML, by interpreting the existing
|
|
code the best it can and then rebuilding new code from it. That's a better
|
|
approach than trying to process existing code, as you're bound to forget about
|
|
some weird special case somewhere. It handles problems like never-ending
|
|
quotes and tags gracefully.
|
|
|
|
* It will remove additional "<" and ">" characters that people may try to
|
|
sneak in somewhere.
|
|
|
|
* It supports checking attribute values for minimum/maximum length and
|
|
minimum/maximum value, to protect against Buffer Overflows and Denial of
|
|
Service attacks against WWW clients and various servers. You can stop
|
|
<iframe src= width= height=> from having too high values for width and height,
|
|
for instance.
|
|
|
|
* It has got a system for whitelisting URL protocols. You can say that
|
|
attribute values may only start with http:, https:, ftp: and gopher:, but no
|
|
other URL protocols (javascript:, java:, about:, telnet:..). The functions that
|
|
do this work handle whitespace, upper/lower case, HTML entities
|
|
("javascript:") and repeated entries ("javascript:javascript:alert(57)").
|
|
It also normalizes HTML entities as a nice side effect.
|
|
|
|
* It removes Netscape 4's JavaScript entities ("&{alert(57)};").
|
|
|
|
* It handles NULL bytes and Opera's chr(173) whitespace characters.
|
|
|
|
* There is both a procedural version and an object-oriented version of kses.
|
|
|
|
|
|
* USE IT *
|
|
|
|
|
|
It's very easy to use kses in your own PHP web application! Basic usage looks
|
|
like this:
|
|
|
|
|
|
<?php
|
|
|
|
include 'kses.php';
|
|
|
|
$allowed = array('b' => array(),
|
|
'i' => array(),
|
|
'a' => array('href' => 1, 'title' => 1),
|
|
'p' => array('align' => 1),
|
|
'br' => array());
|
|
|
|
$val = $_POST['val'];
|
|
if (get_magic_quotes_gpc())
|
|
$val = stripslashes($val);
|
|
# You must strip slashes from magic quotes, or kses will get confused.
|
|
|
|
$val = kses($val, $allowed); # The filtering takes place here.
|
|
|
|
# Do something with $val.
|
|
|
|
?>
|
|
|
|
|
|
This definition of $allowed means that only the elements B, I, A, P and BR are
|
|
allowed (along with their closing tags /B, /I, /A, /P and /BR). B, I and BR
|
|
may not have any attributes. A may only have the attributes HREF and TITLE,
|
|
while P may only have the attribute ALIGN. You can list the elements and
|
|
attributes in the array in any mixture of upper and lower case. kses will also
|
|
recognize HTML code that uses both lower and upper case.
|
|
|
|
It's important to select the right allowed attributes, so you won't open up
|
|
an XSS hole by mistake. Some important attributes that you mustn't allow
|
|
include but are not limited to: 1) style, and 2) all intrinsic events
|
|
attributes (onMouseOver and so on, on* really). I'll write more about this in
|
|
the documentation that will be distributed with future versions of kses.
|
|
|
|
It's also important to note that kses' HTML input must be cleaned of all
|
|
slashes coming from magic quotes. If the rest of your code requires these
|
|
slashes to be present, you can always add them again after calling kses with
|
|
a simple addslashes() call.
|
|
|
|
You should take a look at the documentation in the docs/ directory and the
|
|
examples in the examples/ directory, to get more information on how to use
|
|
kses. The object-oriented version of kses is also worth checking out, and it's
|
|
included in the oop/ directory.
|
|
|
|
|
|
* UPGRADING FROM 0.1.0 OR 0.2.0 TO 0.2.1 *
|
|
|
|
|
|
kses 0.2.1 is backwards compatible with 0.1.0 and 0.2.0, so upgrading should
|
|
just be a matter of using a new version of kses.php instead of an old one!
|
|
|
|
When you're ready to start using 0.2.1's new features, you can read about them
|
|
in the files in the docs/ directory. The ChangeLog also summarizes the new
|
|
features in this release.
|
|
|
|
|
|
* NEW VERSIONS, MAILING LISTS AND BUG REPORTS *
|
|
|
|
|
|
If you want to download new versions, subscribe to the kses-general mailing
|
|
list or even take part in the development of kses, we refer you to its
|
|
homepage at http://sourceforge.net/projects/kses . New developers and beta
|
|
testers are more than welcome!
|
|
|
|
If you have any bug reports, suggestions for improvement or simply want to tell
|
|
us that you use kses for some project, feel free to post to the kses-general
|
|
mailing list. If you have found any security problems (particularly XSS,
|
|
naturally) in kses, please contact Ulf privately at metaur at users dot
|
|
sourceforge dot net so he can correct it before you or someone else tells the
|
|
public about it.
|
|
|
|
(No, it's not a security problem in kses if some program that uses it allows a
|
|
bad attribute, silly. If kses is told to accept the element body with the
|
|
attributes style and onLoad, it will accept them, even if that's a really bad
|
|
idea, securitywise.)
|
|
|
|
|
|
* OTHER HTML FILTERS *
|
|
|
|
|
|
Here are the other stand-alone, open source HTML filters that we currently know
|
|
of:
|
|
|
|
* XSS filter for PHP4 - the filter from Squirrelmail
|
|
PHP
|
|
Konstantin Riabitsev
|
|
http://www.mricon.com/html/phpfilter.html
|
|
|
|
* HTML::StripScripts and related CPAN modules
|
|
Perl
|
|
Nick Cleaton
|
|
http://search.cpan.org/perldoc?HTML%3A%3AStripScripts
|
|
|
|
There are also a lot of HTML filters that were written specifically for some
|
|
program. Some of them are better than others.
|
|
|
|
Please write to the kses-general mailing list if you know of any other
|
|
stand-alone, open-source filters.
|
|
|
|
|
|
* DEDICATION *
|
|
|
|
|
|
kses 0.2.1 is dedicated to Mischa the cat.
|
|
|
|
|
|
* MISC *
|
|
|
|
|
|
The kses code is based on an HTML filter that Ulf wrote on his own back in 2002
|
|
for the open-source project Gnuheter ( http://savannah.nongnu.org/projects/
|
|
gnuheter ). Gnuheter is a fork from PHP-Nuke. The HTML filter has been
|
|
improved a lot since then.
|
|
|
|
To stop people from having sleepless nights, we feel the urgent need to state
|
|
that kses doesn't have anything to do with the KDE project, despite having a
|
|
name that starts with a K.
|
|
|
|
In case someone was wondering, Ulf is available for kses-related consulting.
|
|
|
|
Finally, the name kses comes from the terms XSS and access. It's also a
|
|
recursive acronym (every open-source project should have one!) for "kses
|
|
strips evil scripts".
|
|
|
|
|
|
// Ulf and the kses gang, September 2003
|