Last Call Review of draft-ietf-dime-extended-naptr-
review-ietf-dime-extended-naptr-secdir-lc-kaufman-2011-05-07-00

Request Review of draft-ietf-dime-extended-naptr
Requested rev. no specific revision (document currently at 09)
Type Last Call Review
Team Security Area Directorate (secdir)
Deadline 2011-04-20
Requested 2011-04-14
Authors Jouni Korhonen, Lionel Morand, Mark Jones
Draft last updated 2011-05-07
Completed reviews Tsvdir Last Call review of -?? by Magnus Westerlund
Secdir Last Call review of -?? by Charlie Kaufman
Assignment Reviewer Charlie Kaufman 
State Completed
Review review-ietf-dime-extended-naptr-secdir-lc-kaufman-2011-05-07
Review completed: 2011-05-07

Review
review-ietf-dime-extended-naptr-secdir-lc-kaufman-2011-05-07






I have reviewed this document as part of the security directorate's ongoing effort to review all IETF documents being processed by the IESG.  These comments were written primarily for the benefit of the security area directors.  Document
 editors and WG chairs should treat these comments just like any other last call comments.




 




This document makes some straightforward extensions to the DNS records that support the Diameter protocol (RFC 3588). The goal is to improve performance over the previous approach where in some cases multiple servers would have to be contacted
 to determine which one(s) supported some particular application. As the document notes, there are no security issues beyond those that apply to the base protocol (RFC 3588).




 




So I found nothing objectionable in this document.




 




Unfortunately, the story doesn’t end there. To understand this spec, I had to read the Diameter document. The approach that Diameter takes to configuration using DNS appears to leave a gaping security hole that should be examined by whoever
 is reviewing RFC 3588bis (which is also in final stages of approval). The problem is that TLS (or IPsec) is used to secure the Diameter connections themselves, and shared keys or certificates are used to authenticate the peer entities. But the DNS records
 appear to be used to learn the names of the peer entities which are subsequently authenticated. That means if someone could update DNS they could indicate the Diameter server for some domain was in fact some rogue server. So long as that rogue server could
 be authenticated, it would be trusted to speak for the domain in the context of Diameter.




 




I suspect common practice is to have Diameter server names be manually configured, in which case there is no vulnerability. But without looking at this in detail it would appear that the more flexible autoconfiguration via DNS is not secure.
 If so (I could easily be missing something), there are several ways it could be fixed. DNSSEC would be the obvious solution, but not necessarily the best. DNSSEC is still not widely deployed, and this protocol is unlikely to act as a forcing function. Better
 would be to put some sort of extension in the certificates of Diameter certificates that indicates the domain(s) over which the server has jurisdiction in this context. Yet another option would be some naming convention for finding the name of Diameter servers
 for a particular domain rather than looking them up in DNS.




 




In any case, someone should have a look.




 




                --Charlie