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Re: Mis-diagnosed XSS bugs hiding worse issues due to PHP feature
From: "Siegfried" <admin () zone-h fr>
Date: Sat, 1 Apr 2006 22:24:31 +0200 (CEST)

Recently i saw http://seclists.org/lists/fulldisclosure/2006/Mar/1815.html

The person who found it sent it to me before sending it elsewhere, as i
thought he wouldn't send it to any mailing list, i decided to verify the
information, and the directory traversal isn't just a directory traversal,
if you look at the code, you see this:

----------------------
if(!empty($chemin))     $chemin     = stripslashes($chemin); else $chemin
= $depart;


// ----------------------------------- Sécurité navigation
-------------------------------------------------- //

$chemintotal = $chemin;

// ------------------------------- Récupération des fichiers et
répertoires dans tableau-- //


$handle  = @opendir($chemintotal);
$file    = @readdir($handle);
-----------------------

This poor check doesn't secure anything as it doesn't check slashes, and
it's useless, BUT this isn't just a directory traversal as you can do
http://[target]/dir.php?chemin=/etc/
and it works as well..

I usually don't verify them as i don't have the time, but when i verify
and find incorrect informations, i see that i'm the only one correcting it
(on my site), and many security sites just relay the information because
they don't have the time to verify them too.

You guys of mitre can't make something like a "verification process" ? or
another web site to verify all the informations, i think it becomes really
necessary..

Siegfried


Le Sam 1 avril 2006 19:13, Siegfried a écrit :
About that xss, it was really a normal xss, like i wrote in my second post
(i respect rgod's work because he always made good analysis and good
advisories). But there are indeed many vulnerabilities that are classified
as XSS while they were much more than a XSS, or a XSS in a PHP error
message.

Those XSS issues are actually vulnerabilities that were fixed in PHP 5.1.2
(i know at least 2 examples: an inclusion error message, a missing
function which name is based on user supplied data).

See also:
http://www.derkeiler.com/Mailing-Lists/securityfocus/bugtraq/2005-10/0040.html

There is also this problem with SQL injection vulnerabilities, everyday we
see a bunch of XSS and SQL injection advisories, but who has the time to
check them all? ..

Siegfried

Le Sam 1 avril 2006 10:11, Steven M. Christey a écrit :

In a post-disclosure analysis [1] of a security issue announced by
rgod [2], Siegfried observed that the reported XSS actually originated
from a file inclusion vulnerability, in which the XSS was reflected
back from an error message when the file inclusion failed:

About the xss, it is an xss in the php error message, there are many
php functions returning errors without filtering them, anybody noted
that?

Yes.

I would greatly appreciate some corroboration from the real PHP/web
security experts out there on what I'm about to say.  If true, it
would partly explain why XSS is so rampant in PHP applications.

As I understand it, this behavior is due to an XSS problem in PHP
itself before 5.1.2 (CVE-2006-0208), as announced in January 2006:

  http://www.php.net/release_5_1_2.php

It's not clear if PHP 4.x was affected.

The XSS happens when display_errors and html_errors are enabled - it
won't quote the output from raw error messages.

No doubt many so-called XSS errors these days are the result of this
particular issue in PHP.  They're aren't entirely the application's
fault, although obviously they indicate the lack of strong input
validation.

This can hide much more serious vulnerabilities, like file inclusion,
directory traversal, or SQL injection.  I have mentioned this in the
past, but now we know why this seems to happen so often.
(Application-controlled error handlers can still be subject to XSS of
course, even under a fixed PHP.)

For those who do post-disclosure analysis: there *might* be a
resultant XSS issue if the researcher claims both XSS and another type
of bug in the same affected parameter/component, or if the
researcher's report includes error messages that don't seem to be
sanitizing XSS-tainted output.

- Steve

[1]
http://lists.grok.org.uk/pipermail/full-disclosure/2006-March/044756.html

[2] http://retrogod.altervista.org/claroline_174_incl_xpl.html


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