0

Target code:

if($(location.href.split("#")[1])) {
  var target = $('#'+location.href.split("#")[1]);
  if (target.length) {
    $('html,body').animate({
      scrollTop: target.offset().top - 160 //offset height of header here too.
    }, 1000);
    return false;
  }
}

It uses from location.href, so I though about using an injection script like this: target-url.com/#"+alert(1)+"", escaping the string and placing an alert(1) to trigger an alert in the page. If I edit the script using Chrome Dev tools, the script is successfully executed:

enter image description here

But when trying to inject this script in the URL, analyzing the browser console, I see a jQuery error:

jquery.js?ver=1.11.3:2 Uncaught Error: Syntax error, unrecognized expression: %22+alert(1)+%22%22. It appears to fail because it's replacing " with %22. But I need to scape the string scope, since location.href.split("#")[1] returns a string, and I need to leave the string scope to run the script.

Is there a way to bypass this URL encoding or this scenario is not exploitable at all?

2

Is there a way to bypass this URL encoding

No, modern browsers correctly URL encode this value, and that cannot be bypassed.

But that's not the only problem. There's actually no double-quoted string here which you could escape with " (nor a single-quoted one which you could escape with ').

There was a jQuery vulnerability in earlier version where $('#<img src=x onerror=alert(1)>') would lead to XSS, but that is fixed in recent versions.

$('<img src=x onerror=alert(1)>') still leads to XSS, but there is no way to get rid of the # (and the URL encoding would also still be in the way).

Given all of this, I would say that the code isn't vulnerable.

| improve this answer | |
  • Thanks for the quick answer @tim! So, can we say that window.location.hash is completely safe from XSS injections? Since it's not possible to get rid of # – GGirotto Mar 29 at 17:34
  • @GGirotto I meant the # in $('#', not from the URL. Nothings ever completely safe, but at least in your example, it would only be exploitable for users who use severely outdated browsers (which don't URL-encode), and even that only if the app uses an outdated jquery version. There are other situations where incorrectly using location.hash can lead to DOM XSS (see eg the last example here) – tim Mar 29 at 18:10

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