RFC 1535 (rfc1535) - Page 3 of 5

A Security Problem and Proposed Correction With Widely Deployed DNS Software

RFC 1535               DNS Software Enhancements            October 1993


   The danger of the heuristic search common in current practise is that
   it it is possible to "intercept" the search by matching against an
   unintended value while walking up the search list.  While this is
   potentially dangerous at any level, it is entirely unacceptable when
   the error impacts users outside of a local administration.

   When attempting to resolve a partial domain name, DNS resolvers use
   the Domain Name of the searching host for deriving the search list.
   Existing DNS resolvers do not distinguish the portion of that name
   which is in the locally administered scope from the part that is
   publically administered.

Solution(s)

   At a minimum, DNS resolvers must honor the BOUNDARY between local and
   public administration, by limiting any search lists to locally-
   administered portions of the Domain Name space.  This requires a
   parameter which shows the scope of the name space controlled by the
   local administrator.

   This would permit progressive searches from the most qualified to
   less qualified up through the locally controlled domain, but not
   beyond.

   For example, if the local user were trying to reach:

         from
        starburst,astro.DESERTU.EDU,

   it is reasonable to permit the user to enter just chief.admin, and
   for the search to cover:

        chief.admin.astro.DESERTU.EDU
        chief.admin.DESERTU.EDU

   but not

        chief.admin.EDU

   In this case, the value of "search" should be set to "DESERTU.EDU"
   because that's the scope of the name space controlled by the local
   DNS administrator.

   This is more than a mere optimization hack.  The local administrator
   has control over the assignment of names within the locally
   administered domain, so the administrator can make sure that
   abbreviations result in the right thing.  Outside of the local
   control, users are necessarily at risk.



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