More Than 75% of DNS Servers Vulnerable to DNS Pharming!   - 1,337 Views,

According to a statement released today by Infoblox, “DNS servers are essential network infrastructure that map names (e.g., yahoo.com) to IP addresses (e.g., 66.94.234.13), directing Internet inquiries to the appropriate location. Simply put, domain name resolution conducted by these servers is required to perform any Internet-related request. Should an enterprise or organization’s DNS systems fail, all Internet functions, like email and Web access, simply will not be available.

The survey - conducted by The Measurement Factory and sponsored by Infoblox - consisted of a number of queries carefully designed to determine the relative vulnerability of each name server to attacks or failures due to security or configuration, which can jeopardize network availability.

Survey Results Expose Widespread Vulnerabilities

The most surprising result of the survey showed that between 75 and 84 percent of the name servers investigated provide recursive name services to arbitrary queriers on the Internet. Industry best practices dictate that recursive name services — a form of name resolution that may require 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 requestors. Providing recursion to arbitrary IP addresses on the Internet exposes a name server to both cache poisoning and denial of service attacks. For example, the recent spate of “pharming” attacks exploit name servers that allow recursive queries from any IP address.

The survey also revealed that over 40 percent of the name servers investigated provide zone transfers to arbitrary queriers. 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 requestor exposes a name server to denial of service attacks.

The survey also showed that almost one-third of the name servers that have been set up to provide redundancy for authoritative data are configured on the same IP network segment. As a result, a successful denial-of-service attack on a single network segment or a failure of a limited portion of the customer’s network can result in a loss of authoritative name resolution service, eliminating the intended benefit of installing multiple, redundant DNS servers.

Cricket Liu, vice president of architecture at Infoblox and author of O’Reilly & Associates’ “DNS and BIND,” “DNS & BIND Cookbook,” and “DNS On Windows Server 2003,” commented, “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.”

Remedies to Address DNS Vulnerabilities

According to Liu, there are several simple steps and deployment best practices that enterprises can take to protect against these vulnerabilities and others: 1. If possible, split external name servers into authoritative name servers and forwarders.

2. On external authoritative name servers, disable recursion. On forwarders, allow only queries from your internal address space.

3. If you can’t split your authoritative name servers and forwarders, restrict recursion as much as possible. Only allow recursive queries if they come from your internal address space.

4. Use hardened, secure appliances instead of systems based on general- purpose servers and operating software applications.

5. Make sure you run the latest version of your domain name server software.

6. Filter traffic to and from your external name servers. Using either firewall- or router-based filters, ensure that only authorized traffic is allowed between your name servers and the Internet.

To view more helpful tools for DNS Best Practices, visit: http://www.infoblox.com/library/dns_resources.cfm.

To view the complete survey results, visit: http://dns.measurement-factory.com/surveys/sum1.html”