That's false. Such attacks are possible through a technique called cross-site request forgery (CSRF) that allows a malicious website to force a user's browser to execute rogue actions on a different website. The target website can be a router's administration interface that's only accessible via the local network.
Many websites on the Internet have implemented defenses against CSRF, but routers generally lack such protection.
The new drive-by exploit kit found by Kafeine uses CSRF to detect over 40 router models from a variety of vendors, including Asustek Computer, Belkin, D-Link, Edimax Technology, Linksys, Medialink, Microsoft, Netgear, Shenzhen Tenda Technology, TP-Link Technologies, Netis Systems, Trendnet, ZyXEL Communications and HooToo.
Depending on the detected model, the attack tool tries to change the router's DNS settings by exploiting known command injection vulnerabilities or by using common administrative credentials. It uses CSRF for this as well.
If the attack is successful, the router's primary DNS server is set to one controlled by attackers and the secondary one, which is used as a failover, is set to Google's public DNS server. In this way, if the malicious server temporarily goes down, the router will still have a perfectly functional DNS server to resolve queries and its owner will have no reason to become suspicious and reconfigure the device.
According to Kafeine, one of the vulnerabilities exploited by this attack affects routers from multiple vendors and was disclosed in February. Some vendors have released firmware updates, but the number of routers updated over the past few months is probably very low, Kafeine said.
The vast majority of routers need to be updated manually through a process that requires some technical skill. That's why many of them never get updated by their owners.
Attackers know this too. In fact, some of the other vulnerabilities targeted by this exploit kit include one from 2008 and one from 2013.
The attack seems to have been executed on a large scale. According to Kafeine, during the first week of May the attack server got around 250,000 unique visitors a day, with a spike to almost 1 million visitors on May 9. The most impacted countries were the U.S., Russia, Australia, Brazil and India, but the traffic distribution was more or less global.
To protect themselves, users should check manufacturers' websites periodically for firmware updates for their router models and should install them, especially if they contain security fixes. If the router allows it, they should also restrict access to the administration interface to an IP address that no device normally uses, but which they can manually assign to their computer when they need to make changes to the router's settings.
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