CSS XSS

CSS XSS

By ghost | 12289 Reads |

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It is infact possible to execute an xss vulnerability using CSS. I was reading a few whitepapers yesterday and I came across something interesting about CSS. Microsoft\'s IE actually will allow javascripts to be executed within the style sheet if you use the expres<i></i>sion() function. Example:

test {
width = expres<i></i>sion(100 + \"px\");
}

Now, the interesting thing here is that you don\'t use any of the conventional injects. No Tags, No escapes. Just text.

test {
width = expres<i></i>sion(alert(1));

Interesting… now… how to use this? Many BB\'s allow the color tag to set color. Some filter the inputs to make sure it is a color or such, however; there are exploitable ones out there.

I\'ve also found that this vulnerability will crash Konqueror (atleast on my box and my mate\'s box).

So I suppose here is a new attack vector for XSS\'s. Not really to attack a .css file, though you could use it if you got write permissions. a sneaky place to hide your cookie stealer, but rather more for inline assaults bypassing BB code filters and such.

Enjoy. :D