Posted by Virus Bulletin on Nov 7, 2011
ISP employee suspected of changing DNS cache.
Millions of Internet users in Brazil may have been exposed to malware after the DNS caches of their ISPs were modified to redirect them to servers controlled by cybercriminals.
DNS (Domain Name System) is the system used by computers on the Internet to resolve domain names (e.g. www.virusbtn.com) to the corresponding IP addresses (in this case 188.8.131.52). Computers and routers are configured to use one or more name servers for DNS lookups; commonly these name servers belong to the ISP. Name servers cache results to prevent them from having to contact a domain's authoritative name server every time a customer makes a request for a domain.
By poisoning the DNS cache of a popular name server, attackers are able to send its users to servers they control, even if the user has a clean, fully patched system. In this case, it appears the attackers used a human 'trojan' to poison the DNS cache: a 27-year-old employee of a medium-sized Brazilian ISP has been arrested and is suspected of having participated in a malicious scheme. Researchers at Kapsersky Labs believe similar breaches may have happened at other ISPs.
In the scheme, users trying to access websites such as Google, YouTube and Hotmail, as well as a number of popular Brazilian sites, were shown a warning urging them to install 'security software' to use the site. Unsurprisingly, this software turned out to be a banking trojan.
In a related attack targeting Brazilians companies, security flaws in routers and modems were exploited to change the DNS settings for these devices, once again sending their users to servers controlled by the attackers. In this case, users were prompted to install a Java applet masquerading as an update to FlashPlayer - which in fact proved to be a banking trojan.
With more than 70 million computers connected to the Internet, it is no wonder Brazil is a prime target for cybercriminals. However, as Dmitry Bestuzhev pointed out in his VB2011 presentation on the cybercrime ecosystem, the 70-year old anti-cybercrime laws in the country also make it a rather safe target for them.