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We discovered a new potential threat that we term "Drive-by Pharming". An attacker can create a web page containing a simple piece of malicious JavaScript code. When the page is viewed, the code makes a login attempt into the user's home broadband router and attempts to change its DNS server settings (e.g., to point the user to an attacker-controlled DNS server). Once the user's machine receives the updated DNS settings from the router (e.g., after the machine is rebooted) future DNS request are made to and resolved by the attacker's DNS server.
The main condition for the attack to be successful is that the attacker can guess the router password (which can be very easy to do since these home routers come with a default password that is uniform, well known, and often never changed). Note that the attack does not require the user to download any malicious software - simply viewing a web page with the malicious JavaScript code is enough.
We've written proof of concept code that can successfully carry out the steps of the attack on Linksys, D-Link, and NETGEAR home routers. If users change their home broadband router passwords to something difficult for an attacker to guess, they are safe from this threat.
Additional details on the attack can be found at: http://www.symantec.com/enterprise/security_response/weblog/2007/02/driveby_pharming_how_clicking_1.html
Thanks,
Zulfikar Ramzan
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Zulfikar Ramzan
Sr. Principal Security Researcher
Advanced Threat Research
Symantec Corporation
www.symantec.com
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