PR07-38: XSS on sIFR

Vulnerability Found: 12 November 2007

Vendor contacted: 19 November 2007

Vulnerability fixed: The issue remains unfixed. The developer of sIFR 
was contacted several times but did not respond.

Severity: Medium

Successfully tested on: sIFR 2.0.2

Description:

Sites using sIFR to render fonts/text are vulnerable to a vanilla XSS 
within the "txt" parameter processed by the actionscript in the 
'<fontname>.swf' flash file.

Note: the victim user does NOT need to be authenticated for this 
vulnerability to be exploitable.


HTML injection PoC:

Provided the victim is tricked to load the following URL, he/she would 
be redirected to a third-party site.

https://target.tld/<fontname>.swf?txt=<a 
href="http://www.procheckup.com">click me!</a>

XSS PoC:

http://target.tld/fonts/FuturaLt.swf?txt=%3Ca%20href=%22javascript:alert(document.cookie)%22%3Eclick%20me!%3C/a%3E&textalign=left&offsetTop=-2&textcolor=


Consequences:

An attacker may be able to cause execution of malicious scripting code 
in the browser of a user who clicks on a link to the target website, or 
visits a malicious website that requests such link.

This type of attack can result in non-persistent defacement of the 
target site, or the redirection of confidential information (i.e.: 
session IDs) to unauthorised third parties.


References:

http://www.procheckup.com/Vulnerabilities.php

http://www.mikeindustries.com/sifr


Credits: Jan Fry of ProCheckUp Ltd (www.procheckup.com)


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