PicoCTF - JSut Duck It Up

Write-Ups

Posted on April 15, 2017 as PicoCTF 2017. 1 min read.

JSut Duck It Up - 100 PTS

What in the world could this be?!?!

[]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]]((!![]+[])[+!+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+([][[]]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+!+[]]+(+[![]]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+!+[]]]+(!![]+[])[!+[]+!+[]+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(![]+[])[+!+[]]+(+(!+[]+!+[]+[+!+[]]+[+!+[]]))[(!![]+[])[+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+
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Wow, that's an really strange and huge file. Title of the challenge suggest that it may be connected with JavaScript, so let's do an quick google. After a little bit of fiddling, I've found this: JSFuck. It is an esoteric subset of the JavaScript language that uses only six distinct characters in the source code. The characters are +, !, (, ), [, ].

Pasting this code into the text field, and running it produces an alert.

JSFuck alert

Easy 100pts, right? Great challenge!

Keep learning and stay safe!

~ W3ndige