RE: MIMESweeper For Web 5.X Cross Site Scripting
Hi list,
I've been asked the following question:
"It sounds like the net impact of this vulnerability is that an attacker can
steal cookies for a site the user isn't allowed to visit anyway. In other
words, there aren't going to be any interesting cookies to steal. Is there
more to this attack scenario?"
It's a good question. Here are at least 2 attack scenarios:
1. Stealing user cookie. Since it requires that the client should already have
such a cookie, it requires that the client visit the banned site first. This
situation is minimized to the time window in which the user is logged in and
the site got banned. Can happen in 2 situations:
1. The product blacklist file is updated (automatically, on a daily
basis) with the added blacklisted site.
2. The administrator adds the specific site to the blacklist file.
The attacker will make the product / administrator believe that a site should
be blacklisted - even a short period is enough, to launch the XSS.
2. Phising/Defacement (using HTML Injection). In this scenario, the attacker is
actually using the fact that some site is banned, and replace the page content
with a forged page.
Example:
http://BannedSite.com/<HTML>forged_page_content_in_here</HTML>
The client will think that he is in the requested site (the browser will also
indicate that),but in fact he will see the forged content - sounds to me like
defacement and/or phishing.
Think about a banned bank web site, in which the attacker will replace the
login page and send the credentials to him.
There are more scenarios, but I think that this is bad enough.
________________________________
Erez Metula, CISSP
Application Security Department Manager
Security Software Engineer
E-Mail: erezmetula@xxxxxxxxxxxxxx Mobile: 972-54-2108830 Office:
972-39007530
-----Original Message-----
From: Erez Metula [mailto:erezmetula@xxxxxxxxxxxxxx]
Sent: Monday, July 10, 2006 2:53 PM
To: bugtraq@xxxxxxxxxxxxxxxxx; support@xxxxxxxxxxxxxx;
html-list@xxxxxxxxxxxxxx; full-disclosure@xxxxxxxxxxxxxxxxx;
news@xxxxxxxxxxxxxx; submissions@xxxxxxxxxxxxxxxxxxxxxxx; partners@xxxxxxxxxxx
Subject: RE: MIMESweeper For Web 5.X Cross Site Scripting
MIMESweeper For Web 5.X Cross Site Scripting
I. INTRODUCTION
MIMESweeper For Web is a policy-based content security for web applications. It
analyzes web content and blocks pages or files that are prohibited by the
organizational security policy.
For more Information please refer to:
http://www.clearswift.com/products/msw/msw_web/default.aspx
II. DESCRIPTION
A XSS vulnerability was discovered by Erez Metula. When accessing a URL which
is not permitted the user is redirected to an "access denied" page that is
vulnerable to XSS. The page does not input validate / HTML Encode the input and
displays the data "as is".
Usually this means that it enables an attacker to inject HTML or Javascript
code into users's browsers, and by that bypassing the browser DOM restrictions.
This javascript code can perform actions on behalf of the user, steal
authentication cookies, change the appearance of web pages, perform phishing
,and generally can do everything to the original page.
III. EXPLOITATION
The vulnerability can be exploited by just redirecting the client to some URL
that is restricted by MIMESweeper policy and adding the script at the end of
the URL.
Example PoC:
http://SomeBlackListedSite/<script>PAYLOAD</script>
IV. IMPACT
Using the MIMESweeper capabilities of a central gateway to spread malicious
scripts to users.
An example attack scenario could be that an attacker will redirect many users
(by email, posting in the organization portal, etc.) to some blocked URL and an
accompanying script that will steal their authentication cookies.
V. DETECTION
Detection of this vulnerability involves injecting some HTML tags / scripts to
a blocked URL that will be responded by the MIMESweeper with the vulnerable
page.
VI. WORKAROUND
Clearswift released a patch for this vulnerability, following the initial
contact ¬ification.
The patch can be obtained from:
http://www.clearswift.com/support/msw/patch_MswWeb.aspx
termed as "MIMEsweeper for Web 5.1.15 Hotfix"
VII. VENDOR RESPONSE
Clearswift has been informed on the 27/6/06 by e-mail to their support.
Clearswift released a fixed version of the software.
VIII. DISCLOSURE TIMELINE
27/06/06 Identification of the flaw
27/06/06 Reporting the flaw to clearswift by email
27/06/06 Response from clearswift, asking for more description
27/06/06 Providing the full description to clearswift
28/06/06 Clearswift acknowledge of the vulnerability
06/07/06 Patch released by clearswift
09/07/06 Public advisory
IX. CREDITS
The vulnerability was discovered by Erez Metula.
Erez Metula, CISSP
Application Security Department Manager
Security Software Engineer
E-Mail: erezmetula@xxxxxxxxxxxxxx