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XSS with Relative Path Overwrite - IE 8/9 and lower

You need these 3 components

1) stored XSS that allows CSS injection. : {}*{xss:expression(open(alert(1)))}
2) URL Rewriting.
3) Relative addressing to CSS style sheet : ../style.css

<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" />
<link href="[RELATIVE_URL_INSERTED_HERE]/styles.css" rel="stylesheet" type="text/css" />
Stored XSS with CSS injection - Hello {}*{xss:expression(open(alert(1)))}

Explanation of the vulnerability

The Meta element forces IE’s document mode into IE7 compat which is required to execute expressions. Our persistent text {}*{xss:expression(open(alert(1)))is included on the page and in a realistic scenario it would be a profile page or maybe a shared status update which is viewable by other users. We use “open” to prevent client side DoS with repeated executions of alert. A simple request of “rpo.php/” makes the relative style load the page itself as a style sheet. The actual request is “/labs/xss_horror_show/chapter7/rpo.php/styles.css” the browser thinks there’s another directory but the actual request is being sent to the document and that in essence is how an RPO attack works.

Demo 1 at Demo 2 at MultiBrowser :

From :

Mutated XSS for Browser IE8/IE9

<listing id=x>&lt;img src=1 onerror=alert(1)&gt;</listing>

IE will read and write (decode) HTML multiple time and attackers XSS payload will mutate and execute.