DNS injection can pollute the entire Internet

The Domain Name System is one of the key applications on the Internet since it enables the translation of domain names into IP addresses. There are many usages of the DNS and unfortunately some abuses as well. Since DNS allows to map domain names into IP addresses, a simple attack on the DNS system consist in providing incorrect answers to DNS queries. This can be performed by attackers willing to launch a Man in the Middle Attack but also by some ISPs and some governments to block some websites. Various countries have laws that force ISPs to block some specific websites, for various purposes. In Belgium this technique has been used several times to block a small number of websites, see e.g. http://blog.rootshell.be/2011/10/04/the-great-firewall-of-belgium-is-back/

Some countries have more ambitious goals than Belgium and try to block a large number of websites. Chine is a well-known example with the Great Firewall of China. One of the techniques used in China is DNS injection. In a few words, a DNS injector is a device that is strategically placed inside the network to capture DNS requests. Every time the injector sees a DNS request that matches a blocked domain, it sends a fake DNS reply containing invalid information. A recent article published in SIGCOMM CCR analyses the impact of such injectors [1]. Surprisingly, DNS injectors can lead to pollution of DNS resolvers outside of the country where the injection takes place. This is partially because the DNS is a hierarchy and when a resolver sends a DNS request, it usually needs to query top-level domain name servers. When the path to such a server passes through a DNS injector, even if the actual data traffic will not pass through the DNS injector later, the injector will inject a fake reply and the website will not be reachable by any client of this resolver during the lifetime of the cached information. The analysis presented in the paper shows that this DNS injection technique can pollute a large number of resolvers abroad. The article reports that domains in belonging to .de are affected by the Great Firewall of China.

map to buried treasure

DNS injection (source : [1])

The article on The Collateral Damage of Internet Censorship by DNS Injection should become a must read for ISP operators who are forced by their governments to deploy DNS injectors. In parallel, this should also be a strong motivation to deploy DNSSEC that will enable resolvers to detect and ignore these DNS injections.

[1](1, 2) Anonymous. The collateral damage of internet censorship by dns injection. SIGCOMM Comput. Commun. Rev., 42(3):21–27, 2012. http://doi.acm.org/10.1145/2317307.2317311.