RE: Preventing cross site scripting

["Calderon, Juan C (EM, DDEMESIS)" <Juan.Calderon () ge com>]

I couldn't find the mail, but some one, some time before mentioned a plug-in for MS Exchange or MS outlook which 
converts HTML to RTF format.

I think this approach is a good solution (if no scripting or Form submission is needed), you will simple see the mail 
with format you gave it, but with no interactive functionality. it should be implemented server side, though.

cheers :)

-----Original Message-----
From: Andrew Beverley [mailto:mail () andybev com]
Sent: Thursday, June 19, 2003 1:28 PM
To: webappsec () securityfocus com
Subject: Preventing cross site scripting


I am currently writing a web application that, as a small part of it,
needs to display an email message. Obviously the message is potentially
in html format, which to display could be sent straight to the browser.

I would like to know the best way of filtering out undesirable html. I
understand the best way is to only allow acceptable information, in this
case all the different html formatting tags.

However, there is a lot of tags that are acceptable. Another approach
would be to strip out all the bad stuff such as <SCRIPT>, <OBJECT>,
<APPLET>, and <EMBED> but this is far from ideal because of new tags
becoming available and so on.

Are there any functions available (for php) that will take a html page
as input and strip out all nasty stuff? Does anyone have suggestions as
to how to do this as easy as possible?

Thanks,

Andrew Beverley