Internet Explorer XSS Filter bypass

I always love the XSS technique, it has sometimes that makes the generation of the payload something close to art, where code and creativity found.

I found this quick trick to bypass the IE filter when the output is write inside script tags:

“;alert(document.cookie%2b%0dwindow);//

This works because the filter is looking for document.cookie but inserting the %2b (a + symbol) and %0d (a new line character) it will still render valid JavaScript code and we’ll bypass the filter. It was tested on a Internet Explorer 8 long time ago so maybe Microsoft already patched it!