FirstBlood-#823Reflected XSS using Referer header on /login.php
This issue was discovered on FirstBlood v2

On 2021-10-29, yashamin Level 2 reported:

I found that in /login.php Referer header's value was reflected in <a href='REFLECTION_HERE'>. Here reflection is inside single quotes, so we can use single quote in the path of previous page to break the attribute's value. For example previous page's url should be'__other_attributes__

Also we won't be able to use chars like <, ", and [SPACE] because they will be url encoded referrer header's value will be reflected. To separate multiple attributes we can use slash, like for path /attr1='val1'/attr2='val2', reflected value will be <a href=''/attr1='val1'/attr2='val2'>.

To make the payload work without user interaction, I checked CSS files included in the page to find if there is any animation defined. In the /slider-revolution/revolution/css/settings.css file, I found that there was an animation named rev-ani-mouse. So the payload should have that animation and onanimationend event handler defined, which will be called when the animation ends.


  1. Open
  2. Click on the edit button at top right corner, and change Content-Type to 'text/html' and change body to
    click me

    You'll need to provide referrerpolicy attribute to anchor tag, so it will send the entire URL in Referrer header. You can also use meta tags or Referrer-Policy response header to define referrer policy.

  3. After saving, you'll see a unique URL, you can provide xss payload in the url.
    For my unique URL, URL with the payload will be -'/style='animation-name:rev-ani-mouse'/onanimationend='alert(1)'
  4. Open the above URL and click on the link, and you will see alert.


XSS can be used to execute JS code on victim's browser to perform read/write actions on their data.

P3 Medium

Endpoint: /login.php

Parameter: Referer

Payload: '/style='animation-name:rev-ani-mouse'/onanimationend='alert(1)'

FirstBlood ID: 19
Vulnerability Type: Reflective XSS

The parameter ?ref= on login.php was fixed and instead the use of $_SERVER['HTTP_REFERER']; was used. Patrice tested in Chrome and Firefox and saw it was secure, but some users still use Internet Explorer 10 (governments for example!) and the Referer header is vulnerable to reflective XSS.

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Creator & Administrator

Nice find, thanks for providing a working PoC! Actually when testing this I was only able to reproduce on IE as it seems for me on latest versions of Chrome/FF the ' character was encoded, but perhaps I need to play around some more with this :D