[Owasp-leaders] OWASP DOM based XSS definition, which looked a little off

Achim achim at owasp.org
Tue Oct 22 12:16:47 UTC 2013


Hi Serg,

your 50% correct ;-)

your example 
    http://www.some.site/page.html?default=xss_attack_here

can serve for both, reflected XSS and/or DOM-based XSS.
It's reflected as you described if the server sends it back and then will be
rendered, but it can also be DOM-based if the send back page makes use of
'xss_attack_here' in it's scripts.

In both cases it's entirely processed in the browser.

Does this make sense?
Achim



Am 22.10.2013 13:05, schrieb Serg:
> Hi All
> 
> I've recently had a look at the OWASP DOM based XSS definition, which
> looked a little off.
> 
> The TL;DR version: the DOM based XSS definition according to OWASP (
> https://www.owasp.org/index.php/DOM_Based_XSS) is only 50% correct (or the
> pessimistic view - 50% wrong) and misleading.
> 
> I am basing this on the 'Definition' examples (
> https://www.owasp.org/index.php/DOM_Based_XSS), not the 'Advanced
> Techniques and Derivatives' section.
> 
> The first part of this document is incorrect.
> 
> In layman's terms, the Reflected XSS, request/JS is first sent to the
> server, it is then reflected, as is, in the response, hence the name.
> 
> Example:
> 
> http://www.some.site/page.html?default=xss_attack_here
> 
> Since the query string gets sent to the server and reflected back, this is
> a Reflected XSS, not DOM-based.
> 
> The 'xss_attack_here' part is irrelevant here. As long as it is sent to the
> server and reflected back, it's a Reflected XSS vulnerability. Whether it
> runs in DOM or not is irrelevant, technically everything runs in DOM...
> 
> My understanding of DOM based XSS, is: it is processed entirely in the web
> browser, the request with XSS payload is not sent to the server.
> 
> As far as I know, the only way to achieve that is to use fragment
> identifiers, the part of the URL after the '#' (including '#') is not sent
> to the server as part of the request.
> 
> Based on that, I am fairly certain that the current OWASP definition (
> https://www.owasp.org/index.php/DOM_Based_XSS) is wrong and misleading.
> 
> 
> Thoughts?



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