Over 80 percent of public DNS servers around the world are open to pharming and DoS attacks, according to a new study.
The research by internet testing company The Measurement Factory, on behalf of network company Infoblox, found that 84 percent of authoritative DNS servers connected to the internet allowed recursive name services to arbitrary queries.
Best practices in the industry dictate that recursive name services - a form of name resolution that requires a name server to relay requests to other name servers - should only be enabled on a DNS server for a restricted list of known, trusted requesters. Providing recursion to arbitrary IP addresses on the internet exposes a name server to both cache poisoning and denial of service attacks.
Cache poisoning or "pharming" allows a hacker to redirect traffic away from a real website to a fake one set up by the hacker. From there the hacker then steals a user's account information.
"Given what enterprises are risking - the availability of all of their network services - these results are frightening, especially since there are easy ways to address these issues." said Cricket Liu, vice president of architecture at Infoblox.
The survey of 1.3 million DNS servers worldwide also found that over 40 percent of DNS servers provided zone transfers to arbitrary queries. Like recursive name services, zone transfers, which copy an entire segment of an organization's DNS data from one DNS server to another, should only be allowed for a designated list of trusted, authorized hosts, such as secondary name servers. Offering zone transfers to any requester exposes a name server to denial of service attacks.
According to Liu, there are several simple steps and deployment best practices that enterprises can take to protect against these vulnerabilities and others: