Query name minimization

One new thing you need to add your DNS security policies is “query name minimizations” (RFC 7816). I thought I’d mention it since many haven’t heard about it.

Right now, when DNS resolvers lookup a name like “www.example.com.”, they send the entire name to the root server (like a.root-servers.net.). When it gets back the answer to the .com DNS server a.gtld-servers.net), it then resends the full “www.example.com” query to that server.

This is obviously unnecessary. The first query should be just .com. to the root server, then example.com. to the next server — the minimal amount needed for each query, not the full query.

The reason this is important is that everyone is listening in on root name server queries. Universities and independent researchers do this to maintain the DNS system, and to track malware. Security companies do this also to track malware, bots, command-and-control channels, and so forth. The world’s biggest spy agencies do this in order just to spy on people. Minimizing your queries prevents them from spying on you.

An example where this is important is that story of lookups from AlfaBank in Russia for “mail1.trump-emails.com”. Whatever you think of Trump, this was an improper invasion of privacy, where DNS researchers misused their privileged access in order to pursue their anti-Trump political agenda. If AlfaBank had used query name minimization, none of this would have happened.

It’s also critical for not exposing internal resources. Even when you do “split DNS”, when the .com record expires, you resolver will still forward the internal DNS record to the outside world. All those Russian hackers can map out the internal names of your network simply by eavesdropping on root server queries.

Servers that support this are Knot resolver and Unbound 1.5.7+ and possibly others. It’s a relatively new standard, so it make take a while for other DNS servers to support this.

*** This is a Security Bloggers Network syndicated blog from Errata Security authored by Robert Graham. Read the original post at: http://blog.erratasec.com/2017/08/query-name-minimization.html