As a pentester I came across this scenario:

<script type="text/javascript">

 URL = 'http://example.com?x=input';

I am able to insert a new line with %A0, spaces and almost anything except '. The problem is that I need that ' before making a new line so the JS doesn't break.

I am able to leave it like this:

<script type="text/javascript">

 URL = 'http://example.com?x=input;

After the input and before the ; I need to insert a ' or it won't work... Is there any workaround/bypass on this? I am able to inset / too.

  • Have you tried using web encoded characters like %27 for ' or sending as binary?
    – TinCan
    Nov 2, 2019 at 7:36
  • yes i have tried using %27 and double encoding, however i didn't try binary... i never thought that encoding would work in this scenario Nov 4, 2019 at 4:38

1 Answer 1


That's not XSSable.

(I'm assuming in your scenario angle brackets are blacklisted too. Otherwise, you could obviously close the script tag with </script> and inject a separate script that doesn't use single quotes.)

In JS/ES syntax, a string literal that starts with a single quote needs to be ended with a single quote. Since you can't inject one yourself, you may at most cause a syntax error by introducing unescaped line breaks or escaping the closing single quote with a \. An attacker could use that to prevent execution of the current script which may eventually be chained with other bugs to something more severe. But it's not XSS-exploitable by itself.

  • 1
    Yes they are! thanks for letting me know. learning where the dead ends are is useful for future websites i test. thank you. Nov 1, 2019 at 15:39
  • However, it is still exploitable (not as XSS) because you literally break JS code by making a new line. In the case previously explained i just broke an entire functionality of the website. Nov 4, 2019 at 4:41
  • @Mr.ToxicMan Sure, "you may at most cause a syntax error". This may be helpful in some attack scenarios, but it's certainly not XSS-exploitable.
    – Arminius
    Nov 4, 2019 at 8:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.