Monday, March 18, 2013

Alexa reflected DOM XSS

Alexa Internet, Inc. is a California-based subsidiary company of which provides commercial web traffic data. Once it is installed, the Alexa Toolbar collects data on browsing behavior and transmits it to the Alexa website, where it is stored and analyzed, forming the basis for the company's web traffic reporting. As of 2013, Alexa provides traffic data, global rankings and other information on 30 million websites, and claims that 6 million people visit its website monthly.

When using website I found a reflected DOM XSS that could be used by malicious users to trick innocent visitors.
This vulnerability was present at tags.js from a remote location and the variable "tagSrc" lacked the proper sanitizing.

Vulnerable code:
t.tagSrc = '<div align="center">'+t.tagSrc+'</div>';

When modifying the URL you can inject the code you want:"></script><script>alert(document.cookie);</script><!--&adSpace=miscellanious&center=1&env=display

This issue already has been fixed but it took more than 3 months. It's strange that a company that's so big couldn't fix this type of vulnerability faster.
Malicious users could use this DOM XSS to spread phishing campaigns with a higher success rate.

13 December 2012: Reported this issue.
13 December 2012: Alexa replied and forwarded to engineering team.
26 December 2012: I requested a follow-up. They replied that still unpatched.
15 March 2013: Alexa replied that the DOM XSS has been fixed.


  1. I too found this, but they failed to respond to my emails.. :(

  2. Deepankar, I agree sometimes it's hard to reach the right department. Thanks for sharing your comment.