Paper Notes: Redirecting DNS for Ads and Profit

Redirecting DNS for Ads and Profit is one of the collection of papers from the ICSI team, with the results from the Netalyzr, network diagnosis tool. This paper focuses on the 66K session traces where DNS error traffic has been monetization and calls out Paxfire, for their role in this area, the paper focuses on NXDOMAIN wildcarding and search engine proxying (see my past post on how middleboxes interfere with DNS for an introduction to these techniques). The authors acknowledge the unrepresentative sample of Netalyzr users and the high number of sessions using OpenDNS or Comcast DNS resolvers.

NXDOMAIN wildcarding is not encouraged by ICANN and can have serious implications for non web browser DNS traffic (some resolvers only rewrite lookups starting with www. to try to prevent this). In many cases, redirection servers do not simply use HTTP 302.

The highlight of this paper was the fake NXDOMAIN opt-out offered by Paxfire, where the ad server simply served the user’s browser’s error page.

DNSSEC may provide authenticated denial of existence but this doesn’t necessarily fix the problem, for example Xerocole offers DNS resolvers with the option to simply rewrite DNSSEC signed NXDOMAIN responses without a signature, thus assuming the client will not validate DNSSEC.

OpenDNS wildcards NXDOMAIN and SERVFAIL errors as well as directing users to the redirection server if there server supports only IPv6. This is provided as an option in D-Link routers.

The study observed >12 ISPs using squid proxies to redirect search engine traffic. The study did not observe resolver independent NXDOMAIN redirection but did see NATs redirecting all DNS requests (regardless of resolver) to the configured recursive resolver, thus creating in-path NXDOMAIN rewriting if the new resolver uses NXDOMAIN wildcarding.

This paper is a fun, light read that I would recommend, though its results are a bit out of date now, as it used data from Jan 2010 to May 2011.

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