Re: Question about a security function

On 5/20/2010 11:23 AM, David Otton wrote:

On 20 May 2010 15:52, Al<news@ridersite.org> wrote:

I agree blacklisting is a flawed approach in general. My approach is to strictly confine entry text to a whitelist of benign, acceptable tags. The

But that's not what you've done. You've blacklisted the following patterns: "\<script\x20", "\<embed\x20", "\<object\x20", 'language="javascript"', 'type="text/javascript"', 'language="vbscript\"', 'type="text/vbscript"', 'language="vbscript"', 'type="text/tcl"', "error_reporting\(0\)",//Most hacks I've seen make certain they turn of error reporting "\<?php",//Here for the heck of it. and allowed everything else. A couple of examples: You haven't blacklisted<iframe> <IMG SRC="javascript:alert('XSS');"> would sail straight through that list. I can't tell from that list alone, but are your checks case-insensitive? Because<ScRipT> would pass through a case-sensitive check. We can go on like this all day, and at the end of it you still won't be sure you've blacklisted everything. The first answer at http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags is related, also.

I'm not being clear. First pass is thru the blacklist, which effectually tells hacker to not bother and totally deletes the entry. If the raw entry gets past the blacklist, it must then only contain my whitelist tags. e.g., the two examples you cited were caught by the whitelist parser. And yes, I'm using preg_match() with the "i" arg. Note, my blacklist is not looking for tags per se, just the start of a bad tag. My users are only suppose to be entering plain text with some nice highlighting and lists, etc. The editor will not post anything else. Al...