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I am trying to exploit a reflected cross site scripting in a GET request where the reflection is in the first multi line script block.

It seems I can use every character but <, > and " and the best payload I could come up with is /?search='}]%3Balert(1)%3B%2F%2F

And it gets reflected like this:

<head><script> dataLayer = [{ 'pageType': 'Page', 'category': 'Search', 'searchTerm': ''}];alert(1);//', 'searchResults': '0', }]; </script>

Unfortunately this does not work. Neither does it with /* instead of // to comment out the rest of the script block. Is there any way to make it work without using "<" and ">"? Now it fails with "SyntaxError: unexpected token: ':'"

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  • if needed, you can append the payload with code to re-open a new object in an array: [{ to balance it. – dandavis Nov 15 '18 at 6:20
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You don't need to comment anything out.

Use:

/?search='-alert()-'

JS will attempt to create the search term string from the expression '' - alert() - '' which will trigger the alert function. I preferred - over + because it avoids potential issues with URL encoding and is rarely blacklisted, but you may also use any other binary operators to squeeze in your payload without causing a syntax error.

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  • That actually worked. And this would work in many more cases I assume... :-) I just wasn't aware that you can squeeze the code in the middle of some string using binary operators. Thank you Arminius – 6661620a Nov 16 '18 at 0:43

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